CHAGAS DISEASE: A Latin American Nemesis

Transcription

1 CHAGAS DISEASE: A Latin American Nemesis The following report was prepared by the Institute for OneWorld Health as part of a grant donated by the Bill and Melinda Gates Foundation. The purpose of this report is to review the current status (through 2005) of Chagas disease, assess the possible policy and treatment options, and make appropriate recommendations. This report is not intended to be a comprehensive monograph on Chagas disease. Prepared by: Arthur M. Strosberg, Ph.D., Kimberly Barrio, M.B.A., Valerie H. Stinger, M.B.A., Jessica Tashker, Ph.D., Judith C. Wilbur, Ph.D., Leslie Wilson, Ph.D., and Katherine Woo, Ph.D Institute for OneWorld Health. All rights reserved. i

2 Acknowledgements We would like to thank the following individuals for their helpful discussions and data. Individuals Dr. Dariush Akhavan Dr. Marcelo Aguilar Dr. Byron Arana Dr. Marianela Castillo-Riquelme Dr. Jose Coura Dr. Nilda Cuentas Dr. Dora Feliciangeli Dr. Hugo Gessaghi Robert Felder Dr. Silvia Gold Dr. Felipe Guhl Dr. Ricardo Gurtler Dr. Abraham Jemio Dr. Janis Lazdins Dr. Myriam Lorca Dr. Antonio Luquetti Dr. Jorge Mitelman Dr. Alvaro Moncayo Dr. Silvia Moriana Dr. Joao Carlos Pinto Dias Dr. Francisco Pancera Dr. Carlos Ponce Dr. Janine Ramsey Dr. Perdro Reyes Dr. Antonieta Rojas de Arias Dr. Amadeo Rojas Dr. Gabriel Schmunis Dr. Christopher Schofield Dr. Sergio Sosa Estani Dr. Julio Urbina Dr. Yoshi Yamagata Institutions Pan American Health Organization, Brazil Instituto Nacional de Higiene y Medicina Tropical Leopoldo Izquieta Pérez, Quito, Ecuador Medical Entomology Research and Training Unit/CDC Guatemala London School of Hygiene & Tropical Medicine, London, UK Tropical Medicine Laboratory at the Oswaldo Cruz Institute, Brazil Ministry of Health, Bolivia Universidad de Carabobo, Venezuela Argentine Federation of Cardiologists, Argentina Mundo Sano Foundation, Argentina Mundo Sano Foundation, Argentina University of the Andes, Bogotá, Colombia University of Buenos Aires, Argentina University of Buenos Aires, Argentina The Special Program for Research and Training in Tropical Diseases (TDR), WHO Department of Medicine, the University of Chile Federal University Of Goias, Brazil Chagas Committee Chair, Argentine Federation of Cardiologists, Argentina University of the Andes, Bogotá, Colombia RELCOV Doctors without Borders, Tarija, Bolivia Rene Rachou Institute, Fiocruz System, Brazil University of the Republic, Uruguay Central Reference Lab for Chagas and Leishmaniasis, Honduras Center for Infectious Disease Research, National Institute for Public Health, Mexico National Institute of Cardiology, Mexico Tropical Medicine, Institute of Health Science Research, Universidad National de Asunción, Paraguay Ministry of Health, Bolivia Pan American Health Organization, Washington DC London School of Hygiene & Tropical Medicine, London, UK Coordinator of ECLAT network Epidemiological Services and National Center for Diagnostic and Endemic Epidemic Research, Ministry of Health, Argentina Research Group in Biological Chemistry, Venezuelan Institute for Scientific Research (IVIC) Senior Advisor, Japanese International Cooperation Agency (JICA), Japan i

3 TABLE OF CONTENTS Acknowledgements.i Table of Contents.. ii List of Tables and Figures. iv Glossary...v Brief Summary....1 Introduction....3 Background of Chagas disease... 3 Phases of Chagas disease.. 8 Magnitude of Chagas Disease..12 Geographical Area..12 Prevalence...13 Incidence.13 Mortality.14 Prevention Programs...16 Vector Control Initiatives and their Impact 16 Impact on National Blood Supplies 22 Economic Burden of Chagas Disease.26 Impact on the United States, Canada, and Western Europe 34 United States...34 Canada 36 Spain, Italy, Israel, Australia, and Japan 36 Current Therapy..37 Current Research and Potential New Therapy.39 Drug Research 40 Vaccine Research Basic Research...46 Clinical Trials and Diagnostics Clinical Trials.48 Diagnostics.51 ii

4 Conclusions and Recommendations...55 Conclusions 55 Recommendations..57 Appendix A: Triatominae and T. cruzi Distribution..60 Appendix B: Diagnostic Assays and Clinical Signs.65 Appendix C: Vector Control Initiatives...70 Appendix D: Blood Screening and Seropositivity 77 Appendix E: Cost-Effectiveness of Chagas Disease Interventions in Latin America and the Carribean: Markov Models...80 Appendix F: Drug Classes and Compounds 90 Bibliography (excluding Appendix E)...96 iii

5 List of Tables Table 1. Table 2. Table 3. Table 4. Table 5. Table 6. Triatomine Species and Locations Modes of Chagas Disease Transmission Clinical Manifestations of Chagas Disease Population and Prevalence of Chagas Disease by Region and Country Ecotopes and Insecticide Resistance for Triatomine Species Per Capita Spending on Total Healthcare and Percent Urban Population Table 7A. Prevalence of Chagas Disease in the Latin American Population (in millions): Prevalence Steady State Model With and Without Vector Control Programs Over Time Table 7B. Prevalence of Chagas disease in the Latin American Population (in millions): Prevalence Steady State Model with Vector Control Plus New Drug at Different Cure Rates over Time Table 7C. Prevalence of Chagas Disease in the Latin American Population (in millions): Prevalence Steady State Model With Vector Control Programs Reducing Incidence by 70% or 90% over Time Table 8. Drug Classes and Candidates with Potential for Treating Chagas Disease Table 9. New Diagnostic Techniques for Chagas Disease List of Figures Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Life cycle of T. cruzi Insect-to-host Transmission of Chagas Disease Map of Countries where Chagas Disease is Endemic T. cruzi in Blood Infectious and Parasitic Disease Burden in Latin America and the Caribbean Cost-effectiveness of Intervention Strategies: Effect of Variation in Drug Costs and Efficacy (50% cure rate and 80% cure rate) iv

6 Glossary DALY ECLAT ELISA JICA NDA NVS RELCOV Disability Adjusted Life Year European Community-Latin American Network for Research on the Biology and Control of Triatominae Enzyme Linked Immunosorbant Assay Japanese International Cooperation Agency New Drug Application National Vital Statistics Red Latinoamericana de Control de Vectores v

7 BRIEF SUMMARY Chagas disease (trypanosomiasis) is an insidious, potentially fatal parasitic disease that is widespread in Latin America affecting million or more. It is caused by a flagellate protozoan, Trypanosoma cruzi, which is transmitted primarily by a few species of a blood-feeding triatomine insect known as Vinchuca, the kissing or assassin bug. Chagas disease can also be transmitted via blood transfusion or organ donation, passed congenitally from mother to child via the placenta, or more rarely by ingesting food contaminated with the parasite. Because of international travel and immigration patterns, Chagas disease is cause for epidemiologic concern not only in Latin America but also potentially for the United States, Canada, Spain, Italy, Israel, and Australia. Countries such as Mexico with high rates of U.S. immigration either lack adequate surveillance and spraying programs or are lax about enforcing them. Published reports indicate there may be anywhere from 1 to 2 million people in Mexico infected with Chagas disease. In Latin America, more DALYs (Disability Adjusted Life Years) are lost to Chagas disease than to meningitis, STDs, hepatitis B and C, or malaria; only HIV, diarrheal diseases and TB rank higher. The total number of cases of Chagas disease in Latin America appears to be underreported. Best estimates range from 10 to 14 million infected people, but million prevalence is often reported. Approximately 30% of infected individuals either have or will develop cardiac, peripheral nervous system or digestive system complications within 10 to 30 years after infection. Some individuals will suffer sudden cardiac death. These disease sequelae will continue to place a large economic burden on endemic countries, and hence, Chagas disease control, treatment and premature disability and death constitute a tremendous economic burden for Latin America. The Southern Cone, Andean and Central American Vector Control Initiatives have been highly successful and have led to a significant decrease in primarily the incidence and, to a lesser extent, the prevalence of Chagas disease in selected countries. However, less success has been achieved in other countries and regional spraying programs, which have slackened because of the success of the vector control initiatives, need to be maintained 1

8 in order to avoid rapid reinfestation. This will require financial support from governmental bodies and other groups. Because the flagellate T. cruzi has a sylvatic cycle (i.e. can be maintained among non-human populations), it will be impossible to totally eliminate T. cruzi-infected triatomine vectors. There is a clear need for a safe and effective drug for the treatment of chronic Chagas disease. The ideal drug for Chagas disease would be inexpensive, have few side effects, and be effective during the indeterminate and chronic stages of the disease. While generally successful when used in acute cases, the current standard therapy (benznidazole or nifurtimox) is, at best, only minimally effective in chronic Chagas disease and is associated with significant side effects. The ideal drug would be less toxic and more effective during chronic disease than either benznidazole or nifurtimox. Novel compounds are in early stages of research and at least 10 years from market availability. Potential vaccines have an even more complicated research path and will likely require even more development time. The most desirable approach would be the development of a promising compound currently on the market for another indication (e.g. the antifungal agent posaconazole) that has been shown to be active in animal models of Chagas disease. Better and easier-to-use diagnostic procedures also should be developed that can identify Chagas disease in its symptomatic and asymptomatic stages. In spite of progress made in blood screening technology, more improvements are crucial for both Latin America and the United States. Finally, improvements in commercial reagents and reductions in acquisition costs would significantly improve blood screening for Chagas disease. The most cost-effective program for control of Chagas disease will involve continued maintenance of regional spraying programs accompanied by treatment with a new, safe, and effective drug, manufactured at a cost the intended patient population can afford and which is adequately distributed to that population. Such a program will improve the health and economic status of many impoverished people in Latin America. 2

9 INTRODUCTION Purpose of Report The purpose of this report is as follows: To characterize the nature of Chagas disease, its pathogen and its vectors To describe the prevalence and incidence of Chagas disease in Latin America To relate the present control and prevention measures for the disease To stimulate interest in improving prevention, diagnosis and treatment of Chagas disease To identify a cost-effective strategy to reduce the incidence and prevalence of Chagas disease Background of Chagas Disease Discovery Chagas disease was discovered in 1909 by the Brazilian physician Carlos R.J. Chagas while he was working at the Oswaldo Cruz Memorial Institute in Rio de Janeiro. His work was unique in that he discovered the parasite in the vector insect before describing either the existence of animal reservoirs for the disease or the clinical signs in human beings and animals [23, 108]. DNA obtained from mummified human tissues from the northern coast of Chile indicates that Chagas disease was also prevalent some 4,000 years ago in Latin America [56]. Etiology Chagas disease is caused by the flagellate Trypanosoma cruzi. It is widely spread among small wild mammals (enzootic sylvatic cycle ) such as mice, rats, guinea pigs, and rabbits. The vectors of Chagas disease are insects of the order Hemiptera, family Reduviidae, and subfamily Triatominae. The domestic cycle results from humanvector contact. Humans are the main domestic reservoirs, followed by dogs, cats and domestic rodents. Birds, amphibians and reptiles are naturally resistant to infection, 3

10 while pigs, goats, cattle and horses exhibit only transitory parasitemia and do not play an important role in transmission [23, 36]. Figure 1 shows the life cycle of the flagellate. Figure 1: Life Cycle of T. Cruzi Source:( The population of T. cruzi is not homogeneous, but composed of various strains (see Table 1). Its genetic diversity mainly results from the evolution of independent clones that have remained stable in time and space. A consensus has been reached to group most of the previously described clones into 2 principal subspecies, T. cruzi I and T. cruzi II. While both subspecies cause the human disease, T. cruzi II is more frequently associated with the domestic cycle, while T. cruzi I is more frequently associated with the sylvatic cycle [23]. Chagas disease is detectable over a wide area of Latin America from latitude 42N to latitude 46S. While there are 118 species of triatominae, only a small number are epidemiologically significant as a vector of T. cruzi. 4

11 Table 1: Triatomine Species and Locations Species Region The main source below the Equator in countries South of the T. infestans Amazon basin. Probably introduced from Bolivia into Chile, Argentina, Uruguay, Paraguay and Brazil T. brasiliensis Inhabits the dry regions of Northeastern Brazil Found along the Pacific coast in the North of South America and in T. dimidiate Central America T. sordida Found in Argentina, Bolivia and the dry cerrado in Brazil Rhodnius prolixus From Columbia and Venezuela to Mexico Panstrongylus Inhabits the humid Atlantic forest of Brazil megistus R. prolixus and R. The main vectors in Panama pallescens Sources: [23, 34, 36]. Maps of the distribution of T. brasiliensis, T. dimidiate, T. infestans, P. megistus, R. prolixus and of the distribution of T. cruzi appear in Appendix A. In summary, the principal vectors from Mexico to Venezuela, Columbia, Ecuador, to the north of Peru, and along the Pacific coast are R. prolixus and T. dimidiate (with the exception of R. pallescens in Panama), while T. infestans is the main source of human Chagas disease below the Equator, in those countries south of the Amazonian basin [23, 34, 36]. Transmission and Parasitic Cycle Chagas disease has long been described as a disease of the poor in rural areas. The disease is most often found among those who live in huts constructed of mud, stones or cracked wood, with roofs of grass or palm leaves a perfect breeding ground for triatomine insects. However, with the economic and social changes of the last several decades, rural-urban migration in most endemic areas has increased, and Chagas disease prevalence is no longer limited to rural areas [33, 36]. 5

12 Table 2: Modes of Chagas Disease Transmission Insect wound ( > 80%) Blood transfusion or organ transplant (~15%) Congenital transmission (crosses placenta) (4%) Ingestion of contaminated food (<1%) Lab accident (<1%) After the insect vector/wound route, the second most common route of Chagas disease transmission is by blood transfusion. Migration from rural to urban centers is compromising the safety of the blood supply in many urban areas and increasing the risk of contracting Chagas disease from contaminated blood. The third most common route of transmission of T. cruzi is via congenital transmission. T. cruzi is capable of crossing the placenta, and approximately 4% of babies born to infected mothers are infected with the parasite [37, 145]. It is estimated that as many as 5,000 new infections per year result from congenital transmission. Chagas disease can also be transmitted orally via contaminated foodstuffs. A recent outbreak in Brazil was attributed to contaminated sugar-cane juice. This outbreak caused 31 confirmed cases of the disease and 5 deaths. Health officials suspect that triatomines or infected feces were present on the sugar cane before it was crushed. Transmission via organ transplantation is rare, but has occurred. Three cases of Chagas disease were diagnosed in Americans who received kidney, liver, and pancreas transplants from an unidentified Central American donor in 2001 [26]. Over 80% of human Chagas disease is attributable to vector transmission [34, 117]. 6

13 Laboratory accidents have been responsible for some cases of Chagas disease. Health care or laboratory workers can be infected through contaminated needle puncture or by splashing contaminated culture medium into the eyes or mouth [15]. Insect-to-host Transmission Figure 2 shows the life cycle of the flagellate within the human host. Fig. 2 Insect-to-host Transmission of Chagas Disease The infective flagellate form of T. cruzi, the trypomastigote, is found in the blood of the mammalian host (blood typomastigote) and in the terminal part of the digestive and urinary tracts of the vectors (metacyclic trypomastigote). T. cruzi trypomastigotes are shed in the feces of the triatomine and inoculated into humans through the mucosa of the mouth or the conjunctiva of the eyes, or when infected feces are scratched into skin abrasions. Trypomastigotes can infect most vertebrate cells, especially leucocytes and macrophages. In the host cell, they transform into amastigotes, which multiply intracellularly by binary division, inducing inflammatory and immunological responses. These amastigotes are then released into the blood stream as trypomastigotes, where they are able to infect new 7

14 host cells (especially muscle and glia) or are ingested by another triatomine bug to continue the parasite life cycle in the invertebrate host. Trypomastigotes undergo morphological transformation as they pass through the digestive tract of the triatomine insect. In the vector s stomach, most blood trypomastigotes change into epimastigotes and rounded forms (sphaeromastigotes). These epimastigotes actively divide in the vector s intestine and eventually reach the rectum, where final differentiation into infective metacyclic trypomastigotes and release into the bug s feces occurs [23]. Over 80% of human Chagas disease is attributable to vector transmission [34, 117]. Phases of Chagas Disease There are three phases of Chagas disease: the acute phase, the indeterminate phase, and the chronic phase. However, some investigators consider that there are only two phases: the acute phase and the chronic phase (i.e. everything beyond the acute phase). Acute phase This phase may frequently pass unnoticed, although there may be an inflamed swelling at the trypanosome entry site. Symptoms, if they occur, will do so within 7-9 days post-bite and may include fever, tiredness, edema, swelling and reddening at the site of infection, and swelling of the lymph nodes. When this swelling involves the eyelids, it is referred to as Romana s sign, but this symptom occurs in only 1-2% of cases. In some individuals, clinical signs may also include hepatosplenomegaly, adenopathies, electrocardiographic (ECG) abnormalities (e.g. low QRS voltage), abnormal AV (atrioventricular) conduction, and myocarditis. In approximately 90% of individuals, the acute disease resolves spontaneously. Mortality, resulting from acute myocarditis or meningoencephalitis, occurs during the acute phase in less than 5% of children under two years of age [23]. Due to the high level of parasites in the blood, direct microscopic methods can be used to diagnose Chagas disease during the acute phase (see Appendix B). 8

15 Indeterminate phase During this phase, the patient is clinically asymptomatic, and no parasites are detectable in the blood. Indeterminate stage Chagas disease is generally diagnosed by the presence of specific antibodies, but xenodiagnosis (see Appendix B) can be positive in some cases. Some 50-70% of patients in the indeterminate phase never develop known chronic lesions and remain asymptomatic. However, patients in the indeterminate phase are vulnerable to sudden death due to cardiac conduction abnormalities, sometimes without ever having been diagnosed with Chagas disease. The indeterminate phase is diagnosed using indirect methods, including xenodiagnosis, hemoculture, immunological, and molecular methods. Some 70% of patients in the indeterminate phase never develop known chronic lesions and remain asymptomatic. However, patients in the indeterminate phase are vulnerable to sudden death due to cardiac conduction abnormalities, sometimes without ever having been diagnosed with Chagas disease. Chronic phase This phase develops years after infection in some 30% of infected patients. During the chronic phase, organs including the heart, esophagus, colon, and peripheral nervous system can be affected. Destruction of cardiac parasympathetic nerves as well as segmental areas of cardiac sympathetic denervation have been detected in both the indeterminate and chronic phases of Chagas disease. Parasympathetic intramural denervation has been observed to be irregularly dispersed, but mainly affects the esophagus and colon (especially the sigmoid colon). Clinical signs may include cardiac arrhythmias [e.g. frequent ventricular premature beats (PVCs)] and other ECG abnormalities (e.g. right bundle-branch block, left anterior fascicular block, T- inversion, abnormal Q waves, variable AV block, low QRS voltage), 9

16 bilateral ventricular enlargement, ventricular wall thinning, heart failure, apical aneurysms, and mural thrombi. The combination of right bundle-branch block and left anterior fascicular block is typical of Chagas heart disease. Patients in the chronic stage are also vulnerable to sudden death. Megaesophagus and/or megacolon occurs in approximately one-third of chronic cases, of which 20-50% also present with associated cardiomyopathy. Fecal impaction resulting from severe constipation for a few days to 2-3 months (sometimes associated with bouts of bowel obstruction) and sigmoid volvulus are both side-effects of megacolon. The chronic stage of Chagas disease is diagnosed similarly to the indeterminate phase, using indirect diagnostic methods, including immunological and molecular methods (see Appendix B). Chronic Chagas disease is a leading cause of congestive heart failure in Latin America. Treating this costly phase can require extended hospitalization, application of pacemakers and defibrillators, and, in some cases, cardiac transplantation. Chronic Chagas disease is a leading cause of congestive heart failure in Latin America. Treating this costly phase can require extended hospitalization, application of pacemakers and defibrillators, and, in some cases, cardiac transplantation. Clinical Diagnosis Table 3 below describes the signs of the three phases of Chagas disease. Unfortunately, the indeterminate stage is asymptomatic, as can be the acute phase. 10

17 Table 3. Clinical Manifestations of Chagas Disease Phase Acute Signs Immediately follow infection Romana s sign (eyelid swelling), or swelling around triatominae bite locations. Symptoms may be recognized by experienced clinicians or others educated in the disease. Cardiac symptoms include low QRS voltage or abnormal AV (atrioventricular) conduction. Indeterminate Quiescent phase No easily detectable clinical manifestations. Chronic Cardiac symptoms during the chronic phase may include: Frequent ventricular premature beats (PVCs), Right bundle-branch block, Left anterior fascicular block, T- inversion Abnormal Q waves Variable AV block Low QRS voltage GI symptoms during the chronic phase may include: Enlargement of esophagus and/or colon in 33% of chronic cases, of which 20-50% also have cardiomyopathy. The combination of right bundle-branch block and left anterior fascicular block is typical of Chagas heart disease. Ultrasound images are useful for detecting apical aneurysms, ventricular wall hypokinesia, ventricular wall thinning, and ventricular dysfunction. Radiographic studies of the heart, esophagus, and colon may indicate global heart enlargement, esophageal and/or colon dilatation. 11

18 MAGNITUDE OF CHAGAS DISEASE Geographical Area Chagas Disease is endemic in 18 countries (see Figure 3) in Central America (Belize, Costa Rica, El Salvador, Guatemala, Honduras, Mexico, Nicaragua and Panama) and South America (Argentina, Bolivia, Brazil, Chile, Columbia, Ecuador, Paraguay, Peru, Uruguay, and Venezuela). In addition, it is prevalent but less well documented in Guyana, French Guiana, and Suriname [35]. Figure 3. Map of Countries where Chagas Disease is Endemic 12

19 Prevalence Current estimates of the prevalence of Chagas disease range from 9.9 to 14 million infected individuals (see Table 4), with a point estimate of million in 2002 from the WHO [155]. This amounts to approximately 2-3% of the population of Latin America. Historical prevalence data (1975/1985) are listed in Table 4. These data were derived using standardized protocols in order to yield demographically representative, large sample, cross-sectional epidemiological data [82, 115]. There is a higher degree of confidence in the prevalence data of some countries such as Argentina, but a lesser degree in that of other countries such as Mexico. The estimates of current prevalence in Table 4 are given as a range, reflecting the lack of certainty of any single estimate. Although much of the literature referenced in Table 4 suggests that international initiatives to reduce transmission of the disease through vector control (see Appendix C) and screening of the blood supply (see Appendix D) have substantially reduced recorded prevalence over the past two decades, epidemiological data limitations bring the actual reduction in prevalence into question. Accuracy can be compromised by demographic sample design, sample size, diagnostic methods and statistical design. In addition, many prevalence estimates are primarily based on seroprevalence studies of those donating blood, a population that does not well represent those most likely to have Chagas disease. The problem is further compounded by the location of subjects in remote regions and by political and social biases. In summary, all estimates of Chagas disease prevalence from the 1980s through today are based on incomplete data. Investments to support targeted epidemiological studies are needed to generate a more accurate estimate of Chagas disease prevalence in Latin America. Incidence In Uruguay and Chile, as well as in parts of Brazil and Argentina, transmission of the disease has been effectively interrupted by vector control programs. As a result of 13

20 reductions in disease transmission, estimated incidence for all of Latin America has been reduced 70%, from 700,000 new cases per year to 217,000 between 1983 and 2002 [82, 155]. Current estimates of incidence range from 185,000 to 317,000 new cases per year, with a WHO-cited figure of 200,000 new cases per year [153]. Despite significant progress in controlling disease transmission through vector control programs, populations remain at risk. Some countries, such as Mexico, Peru, Columbia, and Ecuador, have not fully implemented vector control programs, and other endemic regions have shown evidence of reinfestation after decentralization of formerly effective programs. Reinfestation of previously vector-free regions will have significant implications for disease incidence in the next decade. The chronic nature of Chagas disease also has implications for transmission. Transmission via blood transfusion is a concern in both endemic and non-endemic countries (see pg. 22), and the likelihood of congenital transmission from an infected mother to her fetus has been estimated at %. In Argentina, where vector transmission has been effectively interrupted, congenital transmission of the disease is ten times more likely than vector transmission [59]. Mortality Due to the lack of an adequate reporting system, Chagas disease mortality is chronically underreported. Current WHO estimates of annual mortality have declined from more than 45,000 to between 13,000 and 21,000 individuals [155], although other sources estimate that the mortality due to Chagas disease in Mexico alone may be as high as 25,000. If so, total annual mortality due to Chagas disease may be closer to 50,000. It must be noted that the available statistical data for Chagas disease represents a best effort by concerned parties. However, given that recorded mortality data in National Vital Statistics Registries is less than half of the mortality observed in medically supervised cases of Chagas disease, it must be assumed that the National Vital Statistics (NVS) mortality estimates are too low. 14

21 Table 4. Population and Prevalence of Chagas Disease by Region and Country Region/ Country Estimated Prevalence 1975/85 1 Population 2002 (000) 2 Estimated Prevalence Rate 2002 (%) Estimated Prevalence Ranges 2002 Prevalence Source References 2002 CONSERVATIVE HIGH Southern Cone 8,124, , ,564,417 6,970,063 Argentina 2,640,000 37, ,671,164 2,202,898 [28, 33] Boliva 1,300,000 8, ,642,550 2,074,800 [79, 83] Brazil 3,600, , ,961,000 2,291,341 [3, 119] Chile 150,000 15, ,452 93,678 [33, 83] Paraguay 397,000 5, , , 000 [83, 130] Uruguay 37,000 3, ,391 20,346 [82, 83] Andean Initiative 3,121, , ,879,700 3,240,498 Colombia 900,000 43, ,000 1,305,780 [57] Ecuador 400,000 12, , ,000 [1] Peru 621,000 26, , ,000 PAHO/ Moncayo Venezuela 1,200,000 25, ,700 1,084,718 [2, 98] Central America 2,697,600 37, ,966 1,881,651 Belize [104, 128] Costa Rica 130,000 4, , ,000 [82, 128] El Salvador 900,000 6, , ,750 [82, 128] Guatemala 1,100,000 12, , ,196 [128, 132] Honduras 300,000 6, , ,000 [82, 128] Nicaragua 67,000 5, , ,055 [82, 128] Panama 200,000 3,064 < , ,000 [100, 128] Mexico 1,564, , ,605,872 2,100,479 [80, 107] Total-18 Countries 15,507, , ,835,955 14,192,691 1 Prevalence estimates for 1975/85 were derived from [36, 52, and G. Schmunis, personal communication]. 2 Population data was taken from [92]. 15

22 PREVENTION PROGRAMS The Vector Control Initiatives and Their Impact There are currently three regional initiatives for vector control of Chagas disease: the Southern Cone, the Andean Pact, and the Central American Initiatives. All three initiatives aim to reduce the incidence of Chagas disease through vector control programs, blood supply screening, and health education. History of the Initiatives In 1947, field trials in Brazil and in Argentina demonstrated that organochlorine insecticides were highly effective against domiciliated triatomine bugs [32, 114, 127]. Consequently, several countries (including Argentina, Brazil, Chile, Uruguay, and Venezuela) initiated regional spraying programs between the 1950s and middle 1970s. The Venezuelan campaign against R. prolixus, which was formally initiated in 1966, was the first large-scale campaign and was highly successful. By 1976, house infestation rate had been reduced from 31.1% to 5.6%, and seroposivity from 44.4% (in a survey) to 11.7% (in ). In the late 1970s, the organochlorine insecticides were replaced by synthetic pyrethroids, which are 2500 times less toxic to mammals than organochlorines. Pyrethroids are fastacting against triatominae and provide control of other domestic pests, such as flies and fleas. Although considerably more expensive per kg than the organochlorine insecticides, they are applied at much lower doses, and comparative studies have shown them to be considerably more cost-effective than organochlorine insecticides [90, 91, 127]. Pyrethroids were also found to be more acceptable to householders because they are odorless and do not stain walls. The history of vector control initiatives demonstrates the importance of political will in Chagas disease control [35]. The first Brazilian national campaign, aimed at eradication of T. infestans, was launched in 1983 and continued through This campaign covered all endemic states and involved comprehensive surveillance of infected locals 16

23 and spraying of infested houses, followed by local vigilance and organized selective respraying where necessary. By 1986, almost 75% of the geographical objectives were attained. In addition, agreements were made with neighboring Paraguay and Uruguay for the control of T. infestans on their side of the border. However, when Brazilian coastal cities were threatened by the return of the yellow fever vector, Ae. aegypti, the Chagas disease campaign became subordinate to a new Ae. aegypti campaign. As a result of this diverted focus, clinical improvements were reversed: The number of hospitalizations due to Chagas disease, which had declined in 1984, 1985, and 1986, increased between 1987 and With the beginning of the Southern Cone Initiative in 1991, the number of hospitalizations due to Chagas disease began to decline once again. In the 1980s, the Chagas disease vector elimination campaign in Brazil became subordinate to a new Ae. aegypti eradication campaign for yellow fever. As a result of this diverted focus, hospitalizations for Chagas disease increased. Resistance of the vectors R. prolixus, T. dimidiate and T. infestans to pyrethroid insecticides has been observed (see Table 5, p.18). Hence, continued vigilance of sprayed as well as non-sprayed villages is necessary. Housing improvement has also been part of some vector control programs, such as in one program carried out in Venezuela [134]. However, this type of investment is often too costly for poor endemic areas, and governments of affected countries do not frequently give priority to the housing of rural populations. In one successful example, 400 homes in Sucre, Bolivia, were improved at a cost per house of $114 plus $93 in donated labor and supplies [82]. This program was a success in terms of houses improved, reduction of chemical spraying, and community involvement. However, appropriate funding and skilled labor are required for successful implementation of housing improvement programs. 17

24 Table 5: Ecotopes and Insecticide Resistance for Triatomine Species R. prolixus A much more efficient vector than T. dimidiata in transmitting T. cruzi [104]. However, R. prolixus appears to be exclusively domestic in Central America and can therefore be eliminated by spraying [41, 129]. Insecticide-resistant strains have also been observed. In Venezuela, an R. prolixus strain resistant to pyrethroid insecticides was collected in the State of Carabobo T. dimidiata Unlike R. prolixus, has several sylvatic ecotopes, is widespread in both peridomestic and domestic habitats, and is not so easily eliminated [161]. Has been observed after residual spraying with pyrethroids in Central America [92]. T. infestans Insecticide spraying alone may prevent reinfestation with this vector. T. infestans strains resistant to some pyrethroid insecticides have been observed in Porto Alegre, Brazil and in parts of Argentina [162]. Therefore, continual vigilance of both sprayed and non-sprayed villages by residents and healthcare personnel is necessary. Maps of the distribution of T. brasiliensis, T. dimidiate, T. infestans, P. megistus, R. prolixus and of the distribution of T. cruzi appear in Appendix A. Costs of Spraying The average cost of spraying per house can differ substantially between regions. For example, the average cost in Guatemala is $9.12, with the insecticide accounting for most of that cost ($6.57). The average cost of spraying per house in the Southern Cone region is less ($4), with salary and transportation, rather than insecticide, accounting for most of that cost [3, 91, 160]. Use of pyrethroid insecticides has substantially reduced the cost of spraying. However, there are significant costs associated with maintenance spraying, which is required to maintain vector control. See Appendix C for a more detailed overview of the vector control initiatives and their member countries, including disease prevalence, blood supply safety, vector control initiatives, the relevant insect vectors, and vector prevalence for each member country. 18

25 The Southern Cone Initiative In a 1991 meeting in Brasilia, the governments of Argentina, Bolivia, Brazil, Chile, Paraguay, Uruguay, and later Peru signed a joint agreement to control Chagas disease by the elimination of the primary vector, T. infestans, as well as populations of other species that might be of local importance. A secondary stated objective was to decrease the risk of Chagas disease transmission through blood transfusion. The underlying rationale behind this agreement was to promote trans-border continuity of national policy for the control of Chagas disease, and thereby decrease the risk of crossborder transportation of vectors or of infected blood products. Each country within the initiative finances its national activities and retains autonomy for program implementation. A meeting of the Southern Cone Commission, coordinated by the Pan American Health Organization, is held annually to discuss operational aims, methods and achievements. The Southern Cone Initiative has been highly successful. Uruguay and Chile were formally certified free of Chagas disease transmission in 1997 and 1999, respectively. Transmission was interrupted in eight states in Brazil by March of 2001, and in 13 of 19 endemic provinces in Argentina by 2002 [82]. Nevertheless, the estimated prevalence of Chagas disease in the Southern Cone region continues to be between 5.6 and 7 million cases. Vector control impacts incidence first with high prevalence rates remaining for many years. From , the countries of the Southern Cone Initiative spent $348 million on vector control. An example of the cost-effectiveness of this vector control initiative is demonstrated by a detailed analysis by Akhaven [3], which shows that Brazil spent $420 million on vector control during the period from 1975 to 1995, with consequent benefits of over $3 billion a return of $7.16 for every dollar spent. The Southern Cone Initiative is the most successful of the three current regional vector control initiates. For detailed information about the Southern Cone Initiative and its member countries, see Appendix C. 19

26 The Andean Pact Initiative The member countries of the Andean Pact Initiative, formed in 1997, are Columbia, Ecuador, Peru and Venezuela. There are an estimated 1.9 to 3.2 million infected people in this region. For detailed information about the Andean Pact Initiative and its member countries, see Appendix C. The Central American Initiative The member countries of the Central American Initiative, formed in 1997, are Belize, Costa Rica, El Salvador, Guatemala, Honduras, Mexico, Nicaragua and Panama. There may be as many as 2 million infected people in Mexico alone, in addition to the estimated 780, million infected people in the rest of the region. This total accounts for approximately 24-28% of the infected population for all of South America. For detailed information about the Central American Initiative and its member countries, see Appendix C. Threat of Reinfestation Successful vector control is threatened by compromised effectiveness during initial spraying and/or interrupted vigilance during the maintenance phase. Decentralization of spraying programs from the central government to provinces, states, or departments has resulted in compromised efficacy. Successful vector control is threatened by: compromised effectiveness during initial spraying interrupted vigilance during the maintenance phase decentralization of spraying programs from the central government 20

27 In one illustrative example, attempts to eliminate T. infestans in Chaco, a semi-arid region that encompasses parts of Argentina, Bolivia, and Paraguay, have met with considerable difficulty due to dwindling resources devoted to vector control. Although current levels of infestation are only approximately one-twentieth of what they were prior to intensive spraying, infestation levels seem likely to return to previous levels in some regions, such as the Santiago del Estero region in northwestern Argentina, because of reduced spraying [58]. Increased infestation levels may result in the resumption of significant transmission within three years. Other alarming examples exist. In Bolivia, where home infestation rates have been lowered to around 10% of all homes in many areas, there are still regions where it remains at nearly 35%, either as a result of reinfestation or of vector resistance to insecticides. Reinfestation of some parts of the Andean Region of Colombia has resulted in seroprevalence levels similar to those observed prior to spraying only three years before. Key factors leading to reinfestation Key factors leading to reinfestation by either the original or a different vector include: Inappropriate insecticide application [e.g. missing insects in peridomestic areas, inadequate frequency and/or timing [58]] Dwindling resources and decreased spraying Decentralization of vector control programs Decreased political support Strains resistant to available insecticides. Lack of political commitment to vector control programs can result in poor followthrough and inadequate resource allocation. However, countries that recommit to a strong, well maintained vector control program have had some success. In Venezuela, one of the pioneers in vector control, vigorous spraying brought down the level of R. prolixus to 0.7% in 1990, only to see it rise to 5.2% in 2000 following a relaxation of 21

28 spraying. Following additional spraying, this level has now dropped to less than 1%. Appendix C provides recent prevalence and seroprevalence data from Venezuela. Impact on National Blood Supplies Magnitude of Seropositive Blood Transmission by blood transfusion is the second most common way of acquiring Chagas disease. Regrettably, despite the prevalence of Chagas disease in Latin America, blood screening for T. cruzi is done less often in the region than is screening for HIV, hepatitis B, hepatitis C, or syphilis. Mexico only screens 15% of its supply, leaving close to 1 million units per year unscreened. Only Argentina, Brazil, El Salvador, Peru (as of 2001), Uruguay, and Venezuela report 100% screening for T. cruzi [29]. For detailed information on the magnitude of seropositive blood across Latin America, see Appendix D. While legislation has mandated blood supply screening and prohibited paid donors in almost all countries in Latin America, enforcement of these laws is lax, increasing the possibility of acquiring T. cruzi infection by blood transfusion [123]. Voluntary nonremunerated altruistic donors tend to be the healthiest, and prohibiting paid donors minimizes the likelihood of an infection being transmitted through transfusion. Figure 4. T. cruzi in Blood Source: 22

29 Legislative measures are an important aspect of Chagas disease prevention. Whereas prevalence of seropositive blood units ranged from 2 to 50% prior to legislation, seropositivity rates of transfused blood have clearly decreased since screening and donor legislation took effect (See Appendix D). Yet in , tainted blood may have caused infections in 12 of 17 Latin American countries studied. Infection may arise from the administration of blood components, not just from whole blood. Transmission can occur after administration of packed red cells, platelets, white cells, fresh frozen plasma, and cryoprecipitate. Infection may arise from the administration of blood components, not just from whole blood. Transmission can occur after administration of packed red cells, platelets, white cells, fresh frozen plasma, and cryoprecipitate; platelets especially are known to be highly infective. The risk of transfusion-related transmission is dependent on many factors, including the prevalence of Chagas disease, the infection rate, the number of transfusions performed on a given individual (e.g. polytransfused individuals like hemophiliacs or patients undergoing dialysis), the national screening policy, screening test specificity and sensitivity, and the accuracy of laboratory workers. Based on the assumption that the likelihood of becoming infected by an infected transfusion is 20% [120], the probability of becoming infected by donated blood is approximately 219 per 10,000 units in Bolivia, 50 per 10,000 units in Peru, 24 per 10,000 units in Colombia, 17 per 10,000 in El Salvador and between 2 and 12 per 10,000 in Chile, Ecuador, Guatemala, Honduras, Nicaragua, Paraguay, and Venezuela. However, Mexico s lack of a formal blood screening program results in a much higher risk, with a probability of becoming infected by donated blood of 1,912 per 12,750 transfused units [60]. Using these figures, blood screening prevented the transfusion of 1,481 infected units and the potential infection of 300 individuals in Central America (exclusive of Guatemala) in 23

30 1996. In the same year, blood screening in Argentina, Brazil, Chile, Ecuador, Paraguay, Uruguay, and Venezuela prevented the transfusion of 36,017 infected units and the potential infection of 7,201 individuals [120]. Implementation of measures to prevent blood transmission of T. cruzi will constitute a necessary burden for the national health services of Latin American countries for years to come. Cost of Blood Screening Programs Unfortunately, there is a scarcity of blood for transfusion throughout the Americas. Latin America has not reached the number of blood donors considered adequate to avoid blood shortages (5% of the population, or the collection of at least 50 blood units per 1,000 inhabitants-- WHO and International Federation of Red Cross and Red Crescent Societies estimates). Thus, screening needs to be as sensitive and specific as possible to avoid both false positives, which result in the discard of badly needed blood, and false negatives, which may result in transmission of the parasite. Given the unreliability of commercial kits, whose sensitivity and specificity has been shown to vary widely [73, 74], performing more than one serological test helps to avoid generating false results. Yet, at least through the middle 1990s, few countries used more than one serological test for blood donor screening [120]. The costs of screening blood and the potential loss of units of blood are a deterrent to screening. The costs of screening blood and the potential loss of units of blood are a deterrent to screening for Chagas disease. However, given the chronic nature of Chagas disease and the high costs of medical treatment, blood screening programs are necessary. Schmunis and others [79, 120, 124] have developed an algorithm to prompt governments to protect their blood supply. When 24

31 applied to current estimates of seroprevalence of Chagas disease in Latin America, the results validate the need for improved blood bank screening. In those areas with shortages of donated blood, where blood with positive serology cannot be discarded, the only measure capable of preventing infection via transfusion is the addition of gentian violet dye to the blood. Gentian violet kills trypomastigotes in vitro at 4 0 C, but has the detriment that patients may become stained blue for short periods of time [36, 89]. The unitary cost for blood screening, estimated from expenditures on the least expensive laboratory reagents in each of 9 Latin American countries, was $0.25 to $1 for a T. cruzi test (ELISA, radioimmunoassay, or indirect hemagglutination). The estimated cost of preventing the transfusion of one T. cruzi infected unit of blood ranged from $11-$209 per positive unit. This wide variation in cost is a reflection of the prevalence of infection and cost of each test in the various countries. Data suggests that tainted blood may have caused infections in 11 out of 17 Latin American countries in 2001 and 2002 [122]. Out of 6.6 million blood unit donations per year in Latin America, over 2 million occur in countries (including Bolivia, Chile, Colombia, Costa Rica, Ecuador, Guatemala, Mexico, Nicaragua, and Panama) that have only incomplete or inadequate screening programs in place. Based on the most conservative estimates, between 500 and 1,385 people were infected with Chagas disease after receiving a tainted blood transfusion every year between 2000 and 2002 [93, 122]. However, these numbers are likely low due to a number of factors, including widely acknowledged underreporting of data, false negatives, lack of quality assurance in screening centers, and the potential of one donor to infect multiple people after blood fractionation [125]. Mexico specifically screens only blood collected in a few so-called endemic areas, although data indicates that seroprevalence rates among blood donors in non-endemic states can be as high as 8% [115]. Based on these numbers, expanded blood testing should be supported for all Latin American countries. 25

32 ECONOMIC BURDEN OF CHAGAS DISEASE Due to the chronic nature of Chagas disease, up to 40% of infected subjects may develop cardiac or digestive system complications well after initial exposure. The comparative disease burden of Chagas disease, measured by DALYs (Disability-Adjusted Life Years) lost, among infectious and parasitic diseases in the region is less than diarrheal diseases, HIV, and TB, but higher than meningitis, STDs (syphilis, chlamydia, gonorrhoea), hepatitis B and C, and malaria (see chart below). In 1990, DALYs for Chagas disease in Latin America were estimated as 2.7 million (1.4 million for males, 1.3 million for females), 1.6 million (0.9 million for males, 0.7 million for females) or 965,000 (535,000 for males, 430,000 for females) depending on which WHO Global Disease Burden report is consulted. However, DALYs are now estimated to be approximately 648,000. Figure 5: Infectious and Parasitic Disease Burden in Latin America DALYs (000s) HIV Di h l TB Ch M i it i STD l H t it i B M l i HIV Diarrheal TB Chagas Meningitis STDs Hep Malaria Diseases Disease (excl. B & C HIV) According to the WHO, total healthcare expenditures in the region (see Table 6) range from an annual per capita spending of $49 to $679 [compared to U.S. annual per capita of $4887] [154]. However, these figures do not well reflect the true costs of the medical treatment of Chagas disease across the region due to inaccurate or no real cost data and to the uncertainty regarding both the number of subjects treated and type of treatment received. For example, the Pan American Health Organization (PAHO) reported in

33 that the total cost of medical treatment for Chagas disease in Bolivia was $21,401,469 in [If each of the 1975/85 estimated 1.3 million Chagas cases were treated, this would average out to $16.46 per patient per year. However, Bolivian costs are said to be about $227 per patient, indicating that many patients are not treated.] Lost productivity due to Chagas disease was estimated at $101,329,492, resulting in a total of $123,551,836 in total direct and indirect costs for Bolivia. In Brazil, the cost of medical treatment (including pacemakers and surgery for megaviscera) is approximately $1,250 per patient, totaling $250 million per year. Absenteeism of afflicted workers accounts for a loss of an additional $620 million, resulting in total direct and indirect costs of $870 million for Brazil. In Chile, the annual cost of treatment for chronic chagasic cardiomyopathy ranges from $439-$584 per patient. Total annual treatment incurs $37 million in private costs and $15 million in government costs, for a total cost of $52 million (exclusive of the costs of lost productivity). In Uruguay, individual patient costs have been estimated at $877, and the total annual cost of medical treatment at $15 million. Indirect costs amount to an additional $25.5 million for a total of $40.5 million in direct and indirect costs. The annual economic loss in Latin America due to early morbidity and mortality from Chagas disease has been estimated to be as high as $18 billion. Countries with larger rural populations generally have higher prevalence rates, less vector control and less available resources for healthcare, and hence are more negatively impacted economically than countries with larger urban populations. 27

34 Table 6. Per Capita Spending on Total Healthcare and Percent Urban Population Country Per Capita Spending, Healthcare, 2001 [USD] [154] Percent Urban Population 2002 [99] Recognized by PAHO as Free of Chagas Disease Transmission Argentina (4 provinces) Brazil (South and Central) Chile Uruguay Vector Control Efforts Progressing Belize Bolivia (Southern) El Salvador Guatemala Nicaragua Paraguay Vector Control Not Yet Fully Implemented Colombia Costa Rica Ecuador Mexico Panama Peru Venezuela Cost-Effectiveness of Prevention Methods and Drug Treatments for Chagas Disease: A Markov model (described in the publication in Appendix E was developed to determine the cost-effectiveness of various prevention methods and hypothetical drug treatments for Chagas disease. Our data, summarized in Figure 6, shows that vector control plus a new drug treatment with a 50% cure rate that costs less than US$45 per case treated, dominates (i.e. is less costly and cures more patients) than the strategy of vector control alone. As costs of a drug with a 50% cure rate increase above $45, this strategy no longer dominates vector control alone, but remains cost effective for the basecase drug cost of $100/case and for all drug costs up to US$350. In the case of a new drug with an 80% cure rate, the strategy of vector control plus new drug treatment dominates that of vector control alone up to the base-case drug cost of US$100. At drug 28

35 costs greater than $100, the strategy of vector control plus new drug treatment no longer dominates vector control alone, but still remains highly cost effective, having a lower cost-effectiveness ratio than the GDP per capita of Latin America. Figure 6: Cost-effectiveness of Intervention Strategies: Effect of Variation in Drug Costs and Efficacy (50% cure rate and 80% cure rate)* Sensitivity Analyis of Cost of Drug Cost Effectiveness of Vector Control Plus Drug Over Vector Control Alone Cost Effectiveness Ratio ($US/QALY) 3,000 2,500 2,000 1,500 1, Drug with 50% Cure Rate Drug with 80% Cure Rate Cost Effectiveness Ratios up until this level are considered "Very Cost Effective" Cost of Drug ($US) * Comparison is vector control alone vs. vector control plus new drug treatment. 29

36 This Markov model was also used to estimate Chagas disease prevalence and mortality over time with and without vector control programs and/or drug treatment. Table 7A shows the estimated Latin American population at different time points from the start of the model in 1990 and demonstrates the disease prevalence by disease phase and deaths avoided over time due to vector control programs. This table demonstrates the dynamics of Chagas disease in Latin America from 1990 and projected to According to our prevalence model, we see that after 10 years the number of the whole Latin American population with Chagas disease is 17.2 million with vector control and 31 million without vector control. After 60 years, the prevalence of Chagas disease decreases to 16.2 million with vector control, and increases to 35.8 million with no vector control, a 19.6 million difference in prevalent cases. Table 7A also demonstrates that after 10 years of vector control programs, 300,000 deaths are avoided, by 30 years, 500,000 deaths are avoided, and by 60 years, 900,000 deaths are avoided. The table also demonstrates that in the absence of vector control programs, the number of chronic disease cases doubles within 60 years. Table 7A. Prevalence and Mortality of Chagas Disease in the Latin American Population (in millions): Prevalence Steady State Model With and Without Vector Control Programs Over Time With Vector Control Alone No Vector Control Total Total Total Total Year No Disease Chronic Disease Chagas Deaths Chagas Prevalence No Disease Chronic Disease Chagas Deaths Chagas Prevalence Table 7B demonstrates the large change in prevalence with the added use of a new drug treatment with a 50 or 80% cure rate when given in the indeterminate or chronic disease phases. This model predicts that prevalence will be immediately reduced to 8.8 million within the first year of treatment availability (year 0) of a drug with a 50% cure rate. This first major impact is lessened over time to maintain a prevalence of about 12 million, years, and 11 million after 60 years. If the cure rate of the new drug 30

37 treatment were 80%, the prevalence after 60 years would be only 8 million. These models demonstrate that most of the reduction in prevalence from both vector control and vector control plus new drug treatment programs comes from delaying those that enter the chronic stage and to a lesser extent decreasing the mortality due to Chagas disease in later years. Table 7B. Prevalence and Mortality of Chagas Disease in the LA 1 Population (in millions): Prevalence Steady State Model With Vector Control Plus New Drug at Different Cure Rates Over Time With Vector Control plus Drug 50% Cure With Vector Control plus Drug 80% Cure Year No Disease Total Chronic Disease Chagas Deaths Total Chagas Prevalence No Disease Total Chronic Disease Chagas Deaths Total Chagas Prevalence LA 1 = Latin American Table 7C demonstrates Chagas prevalence over time in this steady state Markov model when we assume that the vector control programs produce a continuing average reduction across all countries of 70% or 90% in incidence. Since the effectiveness of vector control programs is variable across regions and across time, the actual effectiveness across Latin America could vary from 60-90%. This table demonstrates that prevalence ranges from 12 to 15 million instead of from 14 to 17 million when the effectiveness of the vector control programs is higher. With either estimate, however, our models show persistent prevalence for a number of years, because vector control programs primarily affect incidence in the early years rather then prevalence, which remains relatively stable for at least 50 years. 31

38 Table 7C. Prevalence and Mortality of Chagas Disease in the LA 1 Population (in millions): Prevalence Steady State Model With Vector Control Programs Reducing Incidence By 70% or 90% Over Time With Vector Control Alone: 70% incidence rate reduction Total Chronic Chagas Disease Deaths Total Chagas Prevalence With Vector Control Alone: 90% incidence rate reduction Total Total Chronic Chagas Chagas Disease Deaths Prevalence Year No Disease No Disease In addition, these tables show the number of deaths in Latin America that are avoided with vector control programs (900,000 deaths avoided), and with vector control programs plus a new drug treatment with a 50% cure rate (2.5 million deaths avoided), each compared with no vector control program after 60 years. Tables 7A, B, and C also show increases over time in the number of individuals without disease, decreases for those in the chronic disease stage, and decreases in disease prevalence across time for each intervention. Data generated using our Markov models show that the best results in reducing Chagas disease burden come from a combination of vector control and a new drug treatment that could cure current cases. Our models also demonstrate that vector control alone changes disease prevalence much more slowly than when a new drug treatment is added to vector control efforts. Additionally, the prevalence estimates from our models appear accurate (or only slightly high) and support the conclusion that true prevalence is probably not as low as million, despite very successful vector control programs. This model has several limitations because of various assumptions made. First, as mentioned previously, there is uncertainty about many of the variables used, such as prevalence, mortality, incidence, and treatment costs. We used the best available 32

39 estimates and then tested these with sensitivity analyses, and found the model instructive in demonstrating how these factors change as time passes and as different interventions are used. In addition, we did not change the Latin American population annually to account for prevalence estimates over time when aggregating to the Latin American population, resulting in slightly over-inflated prevalence estimates. Finally, our specifications for the new drug treatment are somewhat speculative and meant to supply information to those currently developing new drug treatments. Many factors are undefined: the accurate ability to identify and treat the disease at an early stage, the possibility that re-treatment would be needed, and that cure would be partial or for fewer patients, and that other treatments would continue to be needed, inflating costs. In spite of this, our estimates seem plausible and conservative. It seems clear that with our current assumptions, both vector control and vector control plus new drug treatment programs will decrease prevalence, morbidity and mortality, are highly cost-effective and probably will continue to be so. As potential new drug treatments and diagnostic testing become better defined, this model can be used with more accurate disease and drug variables. 33

40 IMPACT ON THE UNITED STATES, CANADA, AND WESTERN EUROPE United States The two main risk factors for the transmission of Chagas disease in the U.S. are blood transfusion from infected Latin American immigrants, and travel to endemic areas. It has been estimated that as many as 100,000 Latin American immigrants now residing in the U.S. may be infected with T. cruzi and therefore represent a reservoir for transmission by transfusion. Since 1989, several expert panels to the U.S. FDA have recommended that all donated blood be screened for Chagas disease. Despite the risk of transmission of Chagas disease through infected blood, it was not until December 2006 that the FDA approved a blood screening test for Chagas disease, the ORTHO T. cruzi ELISA test system, manufactured by Ortho-Clinical Diagnostics. This test has been found to be accurate greater than 99% of the time for detecting T cruzi in blood specimens from individuals believed to be infected, while exhibiting little likelihood of false-positive results (2-3/100,000 tests). Prior to this, the only required screening was a verbal questionnaire (often a single question asking if the potential donor has Chagas disease, a fact often unknown by those with the disease) applied in an effort to eliminate those born or having spent long periods of time in endemic areas. Estimates indicate that 1 in every 25,000 U.S. blood donors is infected [61] and at risk for transmitting the disease. Local seroprevalence rates may be considerably greater in some areas; for example, one in 9000 Miami donations, and one in 7500 Los Angeles donations [70]. This same study found that the rate among directed donors, a population with large numbers of at-risk donors, was 1 in 2400 donations. As many as 5% of immigrants in Washington, DC have been reported to be infected with T. cruzi [87]. Another study in Los Angeles reported that the rate for selected high-risk populations may be as high as 1 in 1000 donors [68]. In one study [69], which was conducted among 100,089 low-risk donors in the Southwest Region of the Red Cross, a seroposivity rate of only 1 in 33,000 blood donors was found. However, all 3 positive donors were from a single collection area near Waco, Texas that collects approximately 23% of the blood for the Southwest 34

41 Region. Therefore, in the Waco area, approximately 1 in 7,700 donors were infected with T. cruzi. Interestingly, with respect to these 3 cases, one patient was born in Mexico, while the other two were born in the U.S. and reported no risk factors for infection. A more recent paper (Tobler, Leslie H. et al. Evaluation of a new enzymelinked immunosorbent assay for detection of Chagas antibody in US blood donors. Transfusion, (1):90-96) indicates an observed seroprevalence among donations from a high risk geographic region of the U.S. to be 0.03%. As many as 5% of immigrants in Washington, DC have been reported to be infected with T. cruzi [87]. Another study in Los Angeles reported that the rate for selected high-risk populations may be as high as 1 in 1000 donors [68]. Infection can also result from organ transplantation; three cases of Chagas disease were identified in Americans who received kidney, liver and pancreas transplants from an unidentified Central American donor in 2001 [26]. Chagas Disease carriers also represent an economic burden to the United States should their disease manifest in cardiac symptoms during the chronic phase, resulting in treatment costs and work reduction. One study sponsored by the National Heart, Lung and Blood Institute has calculated that 74,000 Latin Americans residing in the U.S. have chronic chagasic cardiomyopathy (Study ID:4488; Clinical Trials Identifier: NCT ). Although insects (triatominae in Florida) [10] and wild animals (armadillos in Louisiana) [159] infected with T. cruzi are present in many areas of the southern and southwestern U.S., it is unlikely that active transmission through insects will play a large role in T. cruzi infections in the US. Only three cases have been reported in which acute Chagas disease resulted from transmission of the parasite by a vector [118]. The low density of infected insects in the US, as well as our comparatively high standards of housing, are 35

42 undoubtedly the primary factors preventing the usual cycle of transmission from becoming established [64]. Canada Only two cases of Chagas disease associated with blood transfusion have been identified in Canada [21]. Spain, Italy, Israel, Australia, and Japan Estimates of transfusion or transplant risk of Chagas disease in Western Europe are not readily available. However, the same risk factors as in the U.S. and Canada (immigration and travel to disease endemic areas) are present in Western Europe. In 2004, some 400 Latin American immigrants in Barcelona, Spain were found to be infected with Chagas disease [156]. At least one case of transplantation-induced Chagas disease has been reported in Spain in a bone marrow recipient [144]. With the immigration of Latin Americans to Italy, Israel, Australia, and Japan, and in the absence of blood screening measures, cases of Chagas disease should be expected in these countries as well. The low density of infected insects in the US, as well as our comparatively high standards of housing, are undoubtedly the primary factors preventing the usual cycle of transmission from becoming established [64]. 36

43 CURRENT THERAPY The only drugs currently available for the treatment of Chagas disease are nifurtimox and benznidazole. Interestingly, neither drug is on the essential drugs list of most Latin American countries. Both compounds have exhibited significant activity in the acute phase, with up to 80% parasitological cures in treated patients. Their efficacy varies according to the geographical area, probably due to differences in drug susceptibility among the different strains of T. cruzi. However, in the chronic phase, less than 20% of treated patients are parasitologically cured. In spite of this, some studies have demonstrated that there is a significant reduction in deleterious ECG changes and a lower frequency of clinical deterioration after drug treatment during the chronic stage [146]. Nifurtimox (Lampit, Bayer): acts via the reduction of the nitro group to unstable nitroanion radicals, which react to produce highly toxic, reduced oxygen metabolites (superoxide anion, hydrogen peroxide). T. cruzi is deficient in detoxification mechanisms for oxygen metabolites and is more sensitive to oxidative stress than vertebrate cells [113]. Bayer is no longer routinely manufacturing nifurtimox. However, a quantity has recently been manufactured for the treatment of African trypanosomiasis and a small amount of this has been donated to Latin America for the treatment of Chagas disease. Side effects: abdominal or stomach pain, dizziness, headache, anorexia, nausea, vomiting, weight loss, skin rash; rarely, sore throat, convulsions, muscle weakness, numbness, tingling, nervousness. Benznidazole (Rochagan or Radanil, Roche): acts via reductive stress and involves covalent modification of macromolecules by nitroreduction intermediates [113]. 37

44 Side effects: abdominal or stomach pain, diarrhea, nausea, vomiting, convulsions, numbness, tingling pain, weakness in hands or feet, reddish discoloration of skin; rarely, confusion, dizziness, headache, restlessness, sore throat. The side effects of both compounds are probably a result of their oxidative and reductive damage to the host s cells. Although children tolerate these drugs better than adults, clinical trials indicate dropouts on the order of 20 to 30%, because of the side effects of these drugs [145]. A new drug that cures both acute and chronic Chagas disease and has fewer side effects than either nifurtimox or benznidazole is urgently needed. Although children tolerate these drugs better than adults, clinical trials indicate dropouts on the order of 20 to 30%, because of the side effects of these drugs [87]. A new drug that cures both acute and chronic Chagas disease and has fewer side effects than either nifurtimox or benznidazole is urgently needed. 38

45 CURRENT RESEARCH AND POTENTIAL NEW THERAPIES There is a pressing need for a safer and more effective drug for Chagas disease. The only drugs currently available, benznidazole and nifurtimox, are only 80% effective, and only when taken during the acute phase of the disease. Unfortunately, the acute phase is frequently asymptomatic, and many newly infected people are unaware that they have only a short window of time during which to seek effective treatment. Even those newly infected people who are aware of their treatment options may not have access to medicine, or may not complete their treatment regimen because of the intolerable side effects of these drugs, such as pain, fever, vomiting, neuropathy, and severe skin rashes. In cases of delayed diagnosis, when infection is detected years after the initial insect wound, these drugs are at best minimally effective. It must also be noted that nifurtimox has only been intermittently produced since Therefore, access to effective treatment may also be severely compromised by the lack of a continuous and dependable drug supply. The ideal drug for Chagas disease would be inexpensive, have few side effects, and be effective during the indeterminate and chronic phases of the disease, as well as in the acute phase. A drug for Chagas disease with these specifications would improve the health of many impoverished people in Latin America. There are several promising new approaches to the treatment of Chagas disease. Unfortunately, all drugs and vaccines associated with these approaches currently remain in preclinical development or at a discovery research stage. Developing a late-stage or approved compound used for another indication but active for Chagas disease would save years of development time. 39

46 There are several promising new approaches to the treatment of Chagas disease. Unfortunately, all drugs and vaccines associated with these approaches currently remain in preclinical development or at a discovery research stage. There are, however, compounds with anti-t. cruzi activity that are on the market or in NDA stage for other indications. Developing one of these candidates for Chagas disease would save years of development time. Several intriguing possibilities are discussed below. Drug Research The ideal Chagas drug must have appropriate pharmacokinetic properties, including a long terminal half-life and a large volume of distribution. These properties are necessary because T. cruzi parasites are distributed throughout many different tissues, including mucous membranes, cardiac, skeletal and smooth muscle, and glial cells, and the drug must have adequate time to penetrate these tissues. The ideal drug would be effective during both the indeterminate and chronic phases of Chagas disease, as well as in the acute phase. 40

47 A number of drugs have potential to be used for Chagas disease. For more information on each drug class and candidate drug, see Appendix F. Table 8. Drug Classes and Candidates with Potential for Treating Chagas Disease Drug Phase of Drug Class Supporting Data Candidates Development Sterol Biosynthesis Inhibitors Pyrophosphate Metabolism Inhibitors Itraconazole Posaconazole Ravuconazole TAK-187 UR-9825 E5700 ER Voriconazole Risedronate Pamidronate Ibandronate Marketed as Sporanox Marketed antifungal (Schering- Plough) Phase 3 Eisai Unknown (Takeda) Unknown (Grupo Uriach) Unknown (Eisai) Unknown (Eisai) Marketed antifungal (Pfizer) Marketed as Actonel (P&G) Marketed as Aredia (Novartis) Marketed as Boniva (Roche) Human data. Did not resolve parasitemia but was associated with fewer ECG abnormalities in a 9-year follow-up trial. Mouse model data Mouse model data Mouse model data In vitro and mouse model data Mouse model data. Provides full protection against death and parasitemia in mice. Mouse model data. Provides partial protection against death and parasitemia in mice. In vitro and mouse model data In vitro and mouse model data In vitro and mouse model data 41

48 Table 8 cont. Drug Classes and Candidates with Potential for Treating Chagas Disease Drug Class Drug Phase of Candidates Development Supporting Data Preclinical K777 terminated, In vitro data, mouse and dog model hepatotoxicity data (iowh) Thiosemicarbazone Preclinical In vitro activity against amastigotes Cysteine Protease Inhibitors Inhibitors of Purine Salvage Inhibitors of Trypanothione Metabolism Inhibitors of Phosphatidylcholine (PC) Biosynthesis Transialidase Inhibitors Na + H + Exchange Inhibitors Dihydrofolate Reductase Inhibitors compounds 4- aminoazapan- 3-one derivatives Substituted amides and 2- acycloaminobycyclic ketone derivatives Preclinical (GSK) Preclinical Amides Preclinical In vitro Allopurinol Marketed for treatment of gout Activity claimed in one patient In vitro activity against cruzain Some (confliucting) human data. New, more selective inhibitors may have greater therapeutic potential. various Preclinical In vitro activity against parasites Miltefosine unknown unknown unknown Used in treatment of visceral leishmaniasis Preclinical Preclinical Preclinical In vitro activity against parasites Antibodies to parasite transialidase reduced parasitemia in mice through a non-lytic mechanism. Isis Innovation Limited claimed in a patent that DHFR inhibitors could useful in the treatment of parasitic infections. Other potential drugs are inhibitors of Type II isomerase, DNA polymerases, and RNAediting enzymes, as well as immune modulators. These are discussed in Appendix F. Vaccine Research Vaccine development for Chagas disease is still in its early stages. Current strategies focus on both traditional vaccine preparations, such as recombinant subunit vaccines and live attenuated strain vaccines, as well as newer vaccine delivery systems, such as DNA 42

49 vaccines. These efforts will be aided by continuing attempts to identify correlates of immunity and immunogenic antigens. Recombinant Subunit Vaccines Subunit vaccines rely on recombinantly produced antigens to induce a protective immune response in the host. Several parasite antigens have been shown to produce protective immunity in mouse models of Chagas disease, and efforts are underway to identify the next generation of subunit vaccine antigens. Mice have been immunized with experimental subunit vaccines made from recombinant paraflagellar rod proteins and from cruzipain. Immunization with paraflagellar rod proteins is 100% protective against a lethal challenge with T. cruzi [76], and immunization with cruzipain together with IL-12 significantly reduced parasitemia during an acute challenge [126]. These antigens have been shown to generate protective immunity to acute infection, but none have completely blocked parasitemia, which has implications for the ability of these vaccines to prevent the long-term complications associated with chronic Chagas disease. Ongoing efforts to identify other potential antigens will contribute to the generation of new and possibly more effective vaccine candidates. The entire T. cruzi genome has been sequenced by the Institute for Genomic Research, the Seattle Biomedical Research Institute, and the Karolinska Institute Consortium, among other groups [44], and ongoing research at the University of Georgia seeks to characterize approximately 1,000 cloned T. cruzi genes. Better characterization of T. cruzi genes may contribute to better antigen selection for the next generation of experimental subunit vaccines. Live Attenuated Vaccines As with recombinant subunit vaccines, all attempts to create whole cell killed or live attenuated Chagas vaccines have produced only partial immunity [50]. However, further research may indicate that heterologous prime-boost strategies (delivery of antigens via two or more delivery routes or vectors) may produce stronger immunity than homologous 43

50 immunization. Two interesting live whole cell immunization strategies are described below. Immunization of mice with Trypanosoma rangeli, a non-pathogenic protozoan closely related to T. cruzi, reduces mortality and parasitemia during subsequent acute T. cruzi infections [9, 164]. However, T. rangeli immunization was not associated with a strong cell-mediated (Th1-type) immune response. Most experts believe that successful T. cruzi immunization will require a Th1-type response, which is associated with effective responses to intracellular pathogens [62]. Another novel immunization strategy exploits the interesting observation that T. cruzi can multiply inside the murine gastric tract. Mice fed on infected insect excreta show colonization and inflammation in the gastric mucosa and produce mucosal anti-parasite IgA and IgG antibodies. Although a primarily mucosal antibody response may not provide sufficient protection against T. cruzi infections acquired through the bloodstream, this work may have important ramifications for development of long-term complications of Chagas, such as megaviscera [63]. DNA Vaccines Unlike traditional subunit vaccines, which are made up of recombinantly produced disease proteins, DNA vaccines are made up of disease genes delivered to the host either as part of a plasmid vector or inside an attenuated viral vector. Once the host cell takes up the plasmid or virus, the disease genes are translated and transcribed into proteins, which are then presented to the immune system on the surface of Antigen Presenting Cells (APCs). DNA vaccines have been shown to elicit both humoral and cellular immunity. Cellular immunity is thought to be particularly important for combating intracellular pathogens such as T. cruzi amastigotes. One current attempt to develop a DNA-based T. cruzi vaccine is using trypomastigote surface antigen I (TSA-1) as a model antigen. Two different experimental plasmid vaccines containing the TSA-1 gene were constructed and used to vaccinate B6 and BALB/c mice [157]. Survival rates of B6 mice vaccinated with the two plasmid vaccines 44

51 were 73 and 55%, respectively, whereas in BALB/c mice, nearly complete protection (91 and 86% survival, respectively) was observed. Interestingly, in spite of the improved survival, active infection was observed in both strains of mice. In B6 treated mice, the number of circulating parasites was lower than in control DNA recipients; however, in BALB/c treated mice, the observed parasitemia was frequently similar to control DNA recipients. Tc52 protein is an immunosuppressive virulence factor secreted by T. cruzi. This protein acts on cells of the immune system, including macrophages and dendritic cells, to block the production of IL-2, a cytokine necessary for T-lymphocyte proliferation [14]. Studies in mice have shown that immunization with Tc52 genes reduces mortality following experimental infection with T. cruzi. Trans-sialidases (TS) are a family of parasite enzymes that catalyzes transfer of sialic acid from outside sources to the parasite cell surface; this sialic acid coating allows the parasite to evade complement-induced lysis. Immunization with TS genes has been shown to induce a strong antibody response and reduce mortality due to acute infection [48]. This research is very informative and adds to our understanding of the immune response to the parasite. However, DNA vaccines are still many years away from development for use in humans. Basic Research Diagnostics Potential new diagnostic tools, using purified and recombinant antigens, are also being studied. These tools, which are described further in Appendix B, have the potential to streamline conduct of clinical trials for potential new therapies and allow endemic countries to more effectively screen their blood supply. 45

52 Vector Researchers are characterizing the biological and molecular aspects of triatomines. Grisard et al [54] have shown that T. rangeli SC-58 strain, which was isolated in southern Brazil, and H8GS strain (isolated in Honduras) are genetically distinct from other T. rangeli strains. These characterizations are important because they are correlated with different tissue lesions and a clearcut influence of the biological type of strain on the histopathological lesion has been detected. Parasite Basic research in T. cruzi biology is flourishing, especially in Latin America. Ongoing studies into the pathogenesis of the disease are elucidating the response of MHCII T. cells to T. cruzi surface proteins, and cell biologists are studying the ultrastructure of T. cruzi and the role of an early endosomal network in epimastigote vesicle trafficking [106]. Researchers have also identified and cloned many T. cruzi genes, including the immunologically relevant surface glycoprotein antigens GP90 and GP82 [24]. Genomic libraries have been constructed, as have DNA microarrays and cdna libraries using mrna from many different stages of the parasite [7, 52]. As mentioned previously, the entire T. cruzi genome was recently sequenced by The Insititute for Genomic Research and the Karolinska Institute and the Seattle Biomedical Research Institute, among other groups [44]. The sequenced genome may reveal novel targets for drug therapy. 46

53 CLINICAL TRIALS AND DIAGNOSTICS Generating clinical data for new drugs for the treatment of Chagas disease will require reliable diagnostic tools and excellent clinical trial designs. The potential challenges associated with testing a new drug, as well as possible solutions to these challenges, are described in this section. Clinical Trials Conducting clinical trials to determine the efficacy of a new drug for Chagas disease will present many challenges. These challenges fall into three broad categories: trial design, trial logistics, and diagnostics. Trial Design Since subclinical infection results in a very low incidence of clinical events (0.5-1% per year), a large number of patients must be recruited if a trial is to be appropriately powered. For example, a trial following 1000 asymptomatic T. cruzi infected subjects would end up recording events in 10 years (provided no dropout occurs), which would have to be compared between treatment arms. To ascertain a 25% relative risk reduction, a trial having 10% cumulative incidence of events in 10 years of follow-up, with a power of 90%, would need 5,526 participants randomized. For a trial within the same parameters, but with a 5% incidence of events, 11,572 subjects would be needed [145]. Strategies that could identify earlier signs of drug treatment effects may reduce this sample size requirement. Trial Logistics Both rural and urban T. cruzi-infected individuals tend to live in poor conditions, and the difficulties inherent to poor socioeconomic standing may interfere with the completion of long study protocols. The lack of social infrastructure in the countryside and occasional political instability in some regions present additional challenges; it may be difficult to follow some geographically isolated trial subjects over long periods of time. 47

54 Because of these difficulties, investigators have almost always opted for trials with shorter follow-ups and smaller numbers of subjects than were needed to obtain definitive conclusions about drug efficacy. In some respects, inconclusive trials are more costly than having fewer, larger, appropriately-powered trials that lead to definitive conclusions [145]. However, a realistic trial design will have to be of reasonable duration (preferably not longer than 4 years) in order to gain the support of funders, to retain the participation and interest of the Chagas disease clinical community, and, most importantly, to recruit subjects and to maintain adherence to trial protocols over the course of the entire trial. Trial Diagnostics Chagas disease progression is complex. Effective clinical trial protocols will have to describe procedures to accurately diagnose both acute and chronic Chagas disease, as well as determine clinical endpoints that accurately evaluate drug efficacy and reduction or resolution of parasite infection. These three phases of typical Chagas disease progression (acute, indeterminate, and chronic) are associated with different levels of parasitemia in the blood and propagation of the parasite in different tissues. Distinguishing between disease states and detecting parasites during the indeterminate and chronic stages, which are associated with low parasitemia, requires sophisticated and specific diagnostic tools. One possible diagnostic criterion is cardioabnormality. However, although the chronic stage is frequently accompanied by chagasic cardiomyopathy, it is difficult to evaluate subclinical cardioabnormalities in asymptomatic T. cruzi carriers. Additionally, ECG abnormalities, which are not infrequent, can appear and disappear spontaneously over the years. Therefore, the best criterion of cure is proof of the elimination of the T. cruzi parasite, as demonstrated by consistent negative parasitological and serological tests after completion of therapy. Diagnosis of T. cruzi infection is generally made using one of two standard protocols. The first protocol calls for a microscopic examination of anticoagulated blood; visual evidence of parasites is usually a sign of acute infection. However, this test can result in false negatives. When acute Chagas disease is suspected and the standard microscopic 48

55 exam is negative, a hemoculture test, in which patient blood is added to a specialized culture medium to see if parasites multiply, can be attempted [65]. These two tests are relatively insensitive and are not useful for diagnosis of indeterminate or chronic infections, or for diagnosis of congenitally-transmitted infections, all of which are associated with lower parasitemia in the blood. Additionally, the high false negative rate of these tests renders them an inadequate tool for measuring cure rates. Because blood parasitemia does not always reflect disease status, most current diagnostic tests rely on the immune response to the parasite to indirectly detect infection. Specific antibodies, including IgM, IgG, and IgA [75, 136], may be detected in serum during the first clinical manifestations of the acute stage. However, IgM titers decline soon after the acute phase and remain at only basal levels during the chronic phase. The chronic phase is characterized by high levels of IgG, the antibody subtype most associated with the sustained immune response to Chagas disease [17]. All patients with chronic T. cruzi infection have detectable anti-t. cruzi antibodies. Current immunology-based diagnostic assays exploit these antibodies to diagnose chronic Chagas disease. Commercially available diagnostic tests use whole or semi-purified antigenic fractions from T. cruzi epimastigotes (the non-infective form) to capture anti- T. cruzi antibodies, which are then detected by chemiluminescence, among other methods. However, these tests are associated with considerable variation and lack of reproducibility, mainly because of cross-reactions with other pathogens, notably visceral leishmaniasis [27]. These tests also have limited specificity because they do not possess the highly reactive epitopes required to capture IgG/IgM antibodies present in patients with acute or congenital Chagas disease [136]. Newer-generation ELISA tests (described in the next section) use recombinant Chagas antigens to distinguish between disease stages. Usually, two or more serologic tests are employed simultaneously because of their varying specificity. These sophisticated tests will be a great asset to clinical trial design. 49

56 However, seroconversion alone may be an inadequate measure of negative disease state, because seroconversion of chronically infected individuals can take years to complete. Although acute cases are considered cured when antibodies disappear from the blood after twelve months, antibody-based diagnostic methods necessitate years of follow-up to prove that a chronic case has been cured. However, PCR-based diagnostic methods, described in more detail in the next section and in Appendix B, measure very small amounts of parasite DNA in blood or tissue. Although a negative result cannot be interpreted as a definitive cure, continued negative PCR tests, combined with negative serology, may be safely interpreted as indication of disease cure. Diagnostics As described in the previous section, the most common diagnostic procedures for Chagas disease are both expensive and labor-intensive. A simpler, cheaper diagnostic procedure will find widespread use in blood bank screening protocols and in public health applications. Most importantly, good diagnostic tools are required to generate useful clinical trial data. Table 9. New Diagnostic Techniques for Chagas Disease Recombinant These tests are both sensitive and specific for all stages of the antigen ELISA disease and can be configured on cassettes or cards assays Low-cost DNA These tests can be used in the field with little training. tests 50

57 Table 9 cont. New Diagnostic Techniques for Chagas Disease DNA-based assays Complement- Mediated Lysis (CoML) Other Polymerase chain reaction (PCR) is a highly sensitive technique that can be used to detect even small amounts of T. cruzi genetic material in the blood or tissues of patients. PCR has been shown to detect parasite DNA derived from intact, extracellular or recently lysed parasites [19]. Alternatives to PCR-based methods for detecting genetic material include smartdna technology, which is a simple, rapid procedure with a visible color change read-out. However, current assays, many of which are being developed for bioterrorism organisms, do not yet include T. cruzi. CoML detects lytic antibodies that recognize epitopes on the surface of living trypomastigotes. A positive CoML assay indicates the presence of active infection. The absence of lytic antibodies, however, is not necessarily an indication that the patient is parasite-free, because the parasite may persist in tissues in the amastigote form [22]. Decreases in P-selectin and VCAM-1 levels have been observed to correlate with decreases in parasite load [66]. Measurement of these factors may prove useful in evaluation of drug efficacy. An ideal diagnostic test should meet the following criteria: Sensitive, specific and accurate. Able to accurately diagnose all stages of the disease and, if possible, distinguish between acute, indeterminate and chronic stages. Able to become negative or show a rapid significant decrease in reactivity when the parasite is no longer present. Inexpensive and simple to perform. Require little equipment and no refrigeration. Incorporate a method for performance of quality control measures. There are currently two tests that fulfill most of these criteria: new recombinant antigen ELISA assays and new low-cost DNA tests. One new diagnostic test that meets the stringent criteria listed above is the Chagas Stat Pak (Chembio Diagnostic Systems, Medford, NY), a diagnostic test that utilizes three different recombinant antigens to detect anti-t. cruzi antibodies in serum. Unlike 51

58 traditional ELISA tests, the Stat Pak does not require refrigeration and can be performed by untrained personnel. The test requires only 5 µl of serum, and has an easy-to-interpret color-change readout [77]. Data from across Latin America indicates that the Stat Pak shows 98.5 to 100% sensitivity [105]. Recent advances in PCR technology, such as TaqMan (an automated approach based on the use of fluorogenic probes and real-time measurement of the amplification reaction) allow for quantitative analysis of the amount of genetic material in a given sample. Developing appropriate T. cruzi-specific probes could allow for quantitative detection of parasite load before and after drug treatment [18]. One recently developed PCR-based diagnostic procedure involves the detection of T. cruzi kinetoplast DNA (kdna). This procedure uses a hot-start technique, in which oligonucleotides complementary to highly conserved blocks in the kdna minicircle sequence are added to the PCR reaction. This assay is very sensitive and may be useful in detecting infection during the indeterminate phase of the disease. New Assays for Screening the American Blood Supply At the time of the initial writing of this document, both Ortho-Clinical Diagnostics and Abbott Laboratories were developing assays for screening the U.S. blood supply. As indicated on page 34, the Ortho-Clinical Diagnostics assay was approved by the U.S. FDA in December 2006 and is now in use at U.S. blood banks. This assay is a T. cruzi lysate-based ELISA using T. cruzi antigens prepared from lysed epimastigotes and is currently being tested in selected blood banks with likely high risk donor populations. Data indicate a sensitivity of 98.8% and a specificity of 100%. 52

59 Abbott Laboratories (Abbott Park, IL 60064) has been developing a fully automated chemiluminescence immunoassay analyzer that uses recombinant antigens to detect Chagas disease. This analyzer is based on their Prism platform, a fully automated system that uses microparticles and glass fiber membranes for antibody capture and chemiluminescnece for detection (Abbott Laboratories, personal communication). Abbott has licensed 4 recombinant antigens from Corixa: TcF, FP3, FP6, and PF10. Antibodies to these antigens develop at different stages of Chagas disease. Microparticles coated with these antigens are used to capture anti- T. cruzi antibodies in human serum. These antibodies are then detected through chemiluminescence. Current data indicates that the sensitivity of this blood screening assay is 100% (n = 355) and its specificity is 99.92% (n = 6000, 4000 serum samples, 2000 plasma samples). The plan had been to complete feasibility and design validation review by 2006, then perform IND studies for FDA approval in Q2 of The Prism platform is currently marketed outside of the US for Hepatitis assays (HBsAg, HCV) and Retrovirus assays (HIV, HTLV). The target market of the Prism Chagas Assay is the US blood supply and blood banks. 53

60 CONCLUSIONS AND RECOMMENDATIONS Conclusions Chagas disease, or American trypanosomiasis, is caused by the protozoan parasite T. cruzi and afflicts at least million Latin Americans. Its social and economic impact in Latin America has outweighed the combined effects of other parasitic diseases such as malaria, leishmaniasis, and schistosomiasis. In 1993, the World Bank estimated that the comparative disease burden due to Chagas disease, measured by loss of disabilityadjusted life years (DALYs), was 2.74 million [33]. Since then, DALYs due to Chagas disease are reported to have declined to 648,000 in 1996 [88] and, more recently, 667,000 in 2003 [152]. Estimates of the annual mortality rate due to Chagas disease vary widely. In 1990, the WHO estimated that the annual mortality rate was 44,000, whereas the World Bank estimated that it was closer to 23,000 [95]. In 2001, the WHO estimated that this figure had declined to 13,000 [95]. Current estimates of annual mortality due to Chagas disease range from 21,000 to 50,000. Even as DALYs and annual mortality rate estimates decline, however, Chagas disease remains a social and economic drain across Latin America. The WHO estimates that early morbidity and mortality from Chagas disease cause an annual economic loss in Latin America of over $6.5 billion per year [149]; others estimate this figure is closer to between $8 and $18 billion. Spraying programs, designed to eliminate triatominae vectors from domestic habitats, have been progressively implemented throughout Latin America. These spraying programs have been a significant, if incomplete, success story. However, lack of political will has threatened the continued success of these programs, and areas that were once free of triatominae are today threatened with reinfestation. Therefore, the declines that have been observed in disease incidence and mortality in these areas may not continue. 54

61 Continued spraying programs are an important component of Chagas disease control. Even if the disease were eliminated from human populations today, sylvatic insect populations would continue to propagate T. cruzi through infection of wild animals. These sylvatic populations represent a reservoir of T. cruzi beyond the reach of domestic spraying programs, meaning that it will never be possible to completely eradicate Chagas disease from Latin American populations. Additionally, while legislation mandates the screening of blood supplies throughout Latin America, lax enforcement increases the possibility of acquiring T. cruzi infection by blood transfusion [123]. With the immigration of Chagas-infected Latin Americans to the United States, Spain, Australia and Italy, T. cruzi has been detected in the blood supply of these countries. Chagas disease can no longer be viewed as just a disease of the Americas, but rather as a disease of the world. This report indicates that surveillance and vector control must be maintained or there is risk of reoccurrence of transmission in previously controlled areas and that a new drug combined with vector control is the most cost-effective strategy for Chagas disease control. Additionally, diagnostic tools and treatment must be augmented for the newly infected population as well as for the large currently infected population. Regrettably, drug development remains at a standstill, because no market exists to stimulate the interest of pharmaceutical companies. Hence, Chagas disease is one of the most neglected infectious diseases. Therefore, this report underlines the need for a safe and effective drug to treat both the acute and chronic stages of Chagas disease. Drug development will require application of unique diagnostic technology, design and implementation of challenging clinical trials, and manufacturing and distribution of the final drug product to the intended patient population at affordable cost. 55

62 The Institute for OneWorld Health believes that action upon the recommendations in this report can lead to Chagas disease control. However, no comprehensive strategy can be commenced without sufficient resources, collaboration, and cooperation of funding organizations and NGOs, and sustained political interest from decision-makers of governments and public health organizations. Recommendations Maintain current regional surveillance and spraying programs to avoid triatominae reinfestation. Vector control programs have been highly successful in reducing the incidence of Chagas disease in many parts of Latin America. However, political turmoil and the very success of these programs threaten their continued support. Maintaining the success of local spraying and surveillance programs will require both political resolve and continued national funding. Develop a safe and effective drug for the treatment of both acute and chronic Chagas disease. Currently there is no effective drug treatment for chronic Chagas disease. Even in the unlikely event that transmission were completely interrupted throughout the continent, there would remain a patient burden for decades to come. Our results show that a safe, effective, and inexpensive drug for Chagas disease would be a highly cost-effective addition to current treatment and prevention programs, and could potentially save thousands of lives, as well as greatly reduce the number of DALYs (Disability Adjusted Life Years) lost due to Chagas disease. Ideally, research should be supported by philanthropic foundations and governments, since mainstream pharmaceutical companies do not consider Chagas disease patients to be a sufficiently lucrative financial market. 56

63 Explore development of one or more currently approved drugs for treatment of Chagas disease. Many drugs that are either already approved or are in late-stage development for other indications have shown anti-t. cruzi activity in preclinical tests. Although many of these drugs are protected by intellectual property rights, negotiating conditional access or dual market solutions would save years of development time. Currently marketed compounds of interest (and the companies that own them) include: Posaconazole (Noxafil, Schering-Plough) Voriconazole (Vfend, Pfizer) Pamidronate (Aredia, Novartis) Ibandronate (Boniva, Roche) Compounds of interest among those currently undergoing development (and the companies that own them) include: Ravuconazole (Eisai Company, Ltd) TAK-187 (Takeda Chemical Company) E5700 (Eisai Company, Ltd) ER (Eisai Company, Ltd) Develop cheaper, less labor-intensive diagnostics for Chagas disease. More sensitive and specific blood screening tests should be developed. In December 2006, the U.S. FDA approved the Ortho-Clinical Diagnostics ORTHO T. cruzi ELISA blood screening test. This test has now been implemented in U.S. blood banks by the American Red Cross. 57

64 ELISA assays using purified recombinant antigens (such as those produced by Corixa), cassette or card assays, and simple new DNA tests all appear to be promising avenues towards better patient diagnostics. Collaborate with foundations in concert with CDC and PAHO. Together, encourage the government of Mexico to address Chagas disease within its borders. Despite its large share of the estimated million Latin Americans living with Chagas disease, Mexico has no formal vector control program and does not require blood supply screening. Government funding for surveillance studies, regional insecticide spraying, home improvement, disease education, economic impact studies, and treatment should be encouraged. A significant number of Chagas disease-infected Mexican immigrants, as well as infected immigrants from other Latin American countries, now live in the southern United States. Thus, failure to adequately address Chagas disease has ramifications well beyond the borders of endemic countries. Improve housing and provide Chagas disease education in endemic communities. Education about the nature of Chagas disease and the currently available treatments should be provided locally along with housing improvement programs, which are a cost-effective way to reduce the incidence of Chagas disease. Perform economic impact studies to encourage adoption of Chagas disease treatment and prevention strategies. Economic impact studies to support the strategies outlined above are needed. 58

65 APPENDICES FOLLOW 59

66 APPENDIX A: TRIATOMINAE AND T. CRUZI DISTRIBUTION APPENDIX A: TRIATOMINAE AND T. CRUZI DISTRIBUTION P. megistus distribution 60

67 APPENDIX A: TRIATOMINAE AND T. CRUZI DISTRIBUTION R. proxilus distribution T. dimidiata distribution 61

68 APPENDIX A: TRIATOMINAE AND T. CRUZI DISTRIBUTION T. brasiliensis distribution 62

69 APPENDIX A: TRIATOMINAE AND T. CRUZI DISTRIBUTION T. infestans distribution 63

70 APPENDIX A: TRIATOMINAE AND T. CRUZI DISTRIBUTION Map of human infection with T. cruzi 64

71 APPENDIX B: DIAGNOSTIC ASSAYS AND CLINICAL SIGNS APPENDIX B: DIAGNOSTIC ASSAYS AND CLINICAL SIGNS Diagnostic Assays for Acute Disease See the pages immediately following for descriptions of these assays. Direct Microscopic Methods Examination of a fresh drop of anticoagulated blood Examination of stained thin and thick blood smears The microhematocrit method. Indirect Methods Xenodiagnosis Hemoculture Immunological Methods Indirect hemaglutination (IHA) Indirect immunofluorescence (IIF) Enzyme linked immunoabsorbent assay (ELISA or EIA) Complement-mediated lysis (CoML) Molecular Methods Polymerase chain reaction (PCR) Diagnostic Assays for Indeterminate and Chronic Disease See the pages immediately following for descriptions of these assays. Indirect Methods Xenodiagnosis Hemoculture Immunological Methods Indirect hemaglutination (IHA) Indirect immunofluorescence (IIF) Enzyme linked immunoabsorbant assay (ELISA), with recombinant antigens Complement mediated lysis (CoML) Western blot immunodiagnosis Molecular Methods Polymerase chain reaction (PCR) 65

72 APPENDIX B: DIAGNOSTIC ASSAYS AND CLINICAL SIGNS Diagnostic Assays for Chagas Disease Direct Microscopic Methods These methods may only be used for diagnosis during the acute phase of Chagas disease. 1. Examination of a fresh drop of anticoagulated blood. In this method, blood is examined under a 100X field to determine the presence of the parasite. This is the simplest diagnostic technique [23]. 2. Examination of stained thin and thick blood smears. This method can be used if the sample must be transported, but it is less sensitive than examination of fresh blood [23]. 3. The microhematocrit method. This method is based on the buffy coat rapid diagnostic procedure, in which the buffy coat is extracted from whole blood and examined for the presence of parasites [23]. A precipitation method (the Strout method) can also be used [47]. Indirect Methods These tests are less sensitive than other methods, require specialized personnel and extensive time, and are reserved to confirm diagnosis. 1. Xenodiagnosis. In this method, the intestinal contents of triatomine insects are examined for the presence of metacyclic trypomastigotes days after having been allowed to feed on the patient s skin [117]. 2. Hemoculture. In this method, hemocultures are grown on liver infusion tryptose medium over 4-6 months and examined for parasites [81]. Immunological Methods These methods test for the presence of Chagas disease-specific antibodies. These tests will diagnose approximately 90-98% of chronically infected patients, but can be less sensitive for indeterminate stage patients. Depending on the antigens used, cross-reaction with other parasites may occur. Because the sensitivity and specificity of these methods can vary widely, it is recommended that at least two methods be used to confirm diagnosis. 1. Indirect hemaglutination (IHA). This method usually employs antigens from epimastigote and amastigote forms of Y and CL T. cruzi strains. Use of this method requires special training. Its specificity is high, but its sensitivity is lower than other techniques. 2. Indirect immunofluorescence (IIF). This method usually employs antigens from epimastigote forms of T. cruzi and uses fluorescein isothiocyanate-conjugated sheep anti-human immunoglobulin as the secondary antibody. IIF requires training and 66

73 APPENDIX B: DIAGNOSTIC ASSAYS AND CLINICAL SIGNS an expensive UV microscope. It is cheaper than IHA and allows for the processing of a larger number of samples simultaneously. However, readings are subjective, especially in borderline cases, and cross reactions with other parasites, mainly those associated with visceral leishmaniasis, may result in incorrect diagnosis. 3. Enzyme linked immunoabsorbent assay (ELISA or EIA). ELISA tests are frequently performed in 96-well plates, which may require instruments such as washers and spectrophotometers [71, 147]. ELISA-based diagnostic techniques are generally not used in non-specialized laboratories because of the many steps involved. These tests are highly sensitive, but crude antigen-based ELISA tests have low specificity and can result in a wide array of borderline readouts. Specific ELISA assays are described in more detail below. 4. Complement-mediated lysis (CoML). CoML detects anti-t. cruzi antibodies by examining serum-dependent lysis of live parasites. This test can be useful for diagnosing successful treatment, because lytic antibodies disappear from the serum after parasite cure. However, CoML is time-consuming, requires numerous adjustments, and poses risks to lab personnel since it requires the use of live parasites [55]. 5. Western blot immunodiagnosis. Recently, Umezawa and Silveira developed a western blot immunodiagnostic test utilizing trypomastigote excreted/secreted antigens (TESA-BLOT) [137]. This assay tests for antibodies to several parasite antigens, including transialidase, a higher molecular weight SAPA antigen, and a kda exoantigen. The IgGs from chronic Chagas patients react with the kda exoantigen, whereas IgGs/IgMs from acute patients react with the components of SAPA trans-sialidase. Therefore, this assay may allow for discrimination between acute and chronic phases of Chagas disease. Molecular Methods Tests for parasite DNA directly detect infection. These techniques are generally complicated and require special equipment and training. 1. Polymerase Chain Reaction (PCR). Various PCR procedures for detecting Chagas disease have been described [6]. PCR requires a thermostable DNA polymerase, which amplifies DNA that is flanked by known sequences. The known sequences correspond to those on synthetic oligonucleotide primers which are used to initiate the reaction. PCR can be used in many complex ways to achieve different results. However, in the identification of T. cruzi, field studies in low endemic areas have shown that the sensitivity can be less than 50%. This technology will likely be improved. New Diagnostic Methods ELISA Tests New ELISA tests use recombinant antigens to detect disease antibodies in human serum. Recombinant antigen-based ELISA assays are superior to conventional serological 67

74 APPENDIX B: DIAGNOSTIC ASSAYS AND CLINICAL SIGNS assays, which employ whole or semipurified fractions from epimastigote forms of T. cruzi, because they are more specific and are capable of detecting more stages of the disease One new ELISA assay employs a mixture of JL8 and MAP, two T. cruzi antigens that are made up of 14 and 38 amino-acid repeats. ELISAs based on JL8 and MAP were able to detect 84.2% of a group of acute cases form Panama and Brazil, and exhibited a 99.3% specificity and 99.4% sensitivity for sera from Chagasic patients [135]. Another new ELISA test detects antibodies to the T. cruzi enzyme transialidase, which is located on the surface of the parasite. Antibodies to transialidase are present in sera from Chagas disease patients; these antibodies reportedly become undetectable within one to two years after successful treatment. Diagnostic Kits One EIA kit, EIE-Recombinant-Chagas-Biomanguinhos, developed by Oswaldo Cruz Memorial Foundation utilizes recombinant antigens CRA (cytoplasmic repetitive antigen) and FRA (flagellar repetitive antigen) to diagnose chronic stage Chagas disease. It has been found to be 100% specific and 100% sensitive and does not cross react with sera from patients with cutaneous and visceral leishmaniasis [53]. Cassette antibody tests are simple, easy-to-use ELISA-based assays with a visual readout. Cassette antibody tests for Chagas disease have been developed, but are not currently widely available. The Chagas Stat Pak test, which utilizes three different recombinant antigens to detect anti-t. cruzi antibodies in serum, is described in more detail on pages Clinical Signs and Diagnostic Measures Acute phase Romana s sign (unilateral conjunctivitis, palpebral and periorbital edema and preauricular lymphadenopathy resulting from conjunctival contamination with the vector s feces) Other swelling at bite site QRS voltage may be low AV (atrioventricular) conduction may be abnormal Indeterminate phase The indeterminate phase has no easily detectable clinical manifestations Chronic phase EKG abnormalities including frequent ventricular premature beats (PVCs) right bundle-branch block, left anterior fascicular block, T- inversion, abnormal Q waves, variable AV block, and low QRS voltage may occur 68

75 APPENDIX B: DIAGNOSTIC ASSAYS AND CLINICAL SIGNS The combination of right bundle-branch block and left anterior fascicular block is typical of Chagas heart disease Ultrasound images may detect apical aneurysms, ventricular wall hypokinesia, ventricular wall thinning, and ventricular dysfunction Radiographic studies of the heart, esophagus and colon may indicate global heart enlargement, esophageal and/or colon dilatation. 69

76 APPENDIX C: VECTOR CONTROL INITIATIVES APPENDIX C: VECTOR CONTROL INITIATIVES The Southern Cone Initiative Member countries of the Southern Cone Initiative include Argentina, Bolivia, Brazil, Chile, Paraguay, and Uruguay, Argentina Disease Prevalence: Seroprevalence in 18 year old males has dropped from 5.8% in 1981 to 0.5% in % of 0-4 year olds and 1.9% of 0-14 year olds carry the parasite. Estimates of total prevalence range from 1.7 to 2.2 million infected individuals. Blood Supply Safety: There is 100% screening of blood donations in the public sector and 80% in the private sector [148]. Vector Prevalence and Control: The average home infestation rate has fallen from 30% in 1980 to 1% in Transmission has been interrupted in 13 of 19 endemic provinces [133]. Vector: T. infestans Bolivia Disease Prevalence: Estimates of total prevalence range from 1.6 to 2.1 million infected individuals; one report estimated that 29% of the population is infected with T. cruzi. Blood Supply Safety: Infection rates greater than 50% were reported in blood donors in Santa Cruz [25]. Vector Prevalence and Control: The endemic area covers 80% of the country. Vector spraying programs have had a large impact on seropositivity; whereas 22% of 0-4 year olds were infected in Cochamba, a 0% seropositivity rate was found in the equivalent age group in Potosi, which has a successful vector control program. A similar program in Topiza has lowered home infestation rates to 0.8% [97]. Vector: T. infestans 70

77 APPENDIX C: VECTOR CONTROL INITIATIVES Brazil Disease Prevalence: Seroprevalence rates in 7-14 year olds dropped from 18.5% in 1980 to 0.04% in Seroprevalence in 0-4 year olds was 0% in 1999, indicating that vectorial transmission has been interrupted in Brazil. Estimates of total prevalence range from 1.9 to 2.3 million infected individuals. Blood Supply Safety: An initiative to screen 100% of blood was adopted in May, 1998; currently 0.73% of donated blood contains the parasite [84, 151]. Vector Prevalence and Control: Since 1975 there has been a 99.7% decrease in home infestation. Today, only 4 states (Bahia, Tocantins, Goias, Rio Grande) are still considered infested. Vector: The primary vector is T. infestans; secondary vectors are T. brasiliensis and P. megistus Chile Disease Prevalence: Transmission of Chagas disease in Chile has been successfully interrupted. Seroprevalence in the 0-4 years age group decreased from 1.12% in 1995 to 0.016% in Estimates of total prevalence range from 62,000 to 94,000 infected individuals. Blood Supply Safety: Blood bank screening in endemic areas has been mandatory since 1996 and infected samples have been reduced to 0.5%. Vector Prevalence and Control: Home infestation rates were reduced from 3.2% in 1994 to 0.14% in Vector: T. infestans Paraguay Disease Prevalence: Although a 0% prevalence rate in 0-4 year olds in the capital indicates that transmission has been successfully interrupted in some urban areas [96], active transmission still occurs in rural areas. Seroprevalence has decreased significantly in 7-14 years olds since 1972; this decrease may reflect migration of populations away from endemic rural areas. Estimates of total prevalence range from 223,000 to 287,000 infected individuals. Blood Supply Safety: Nearly universal screening in blood banks reduced seropositivity to 5% in 1999 [151]. Vector Prevalence and Control: Home infestation rates were approximately 10-20% in 1982 and have declined only modestly since then. Vector: T. infestans 71

78 APPENDIX C: VECTOR CONTROL INITIATIVES Uruguay Disease Prevalence: Seroprevalence in 0-12 year olds was 0% in These data confirm the interruption of vectorial transmission. Estimates of total prevalence range from 3,400 to 20,300 infected individuals. Blood Supply Safety: 100% of blood donations are screened. Vector Prevalence and Control: Home infestation rate dropped from 5.65% in 1983 to 0.3% in The whole country is under surveillance. Vector: T. infestans The Andean Pact Initiative The member countries of the Andean Pact Initiative, formed in 1997, are Columbia, Ecuador, Peru and Venezuela. Colombia Disease Prevalence: Estimates of total prevalence range from 700,000 to 1.3 million infected individuals. Blood Supply Safety: Blood bank screening has been mandatory since 1995 and there is 100% coverage. Seroprevalence of Chagas decreased from 2.1% of donations in 1998 to 0.65% in Vector Control: Vector control programs have been decentralized to the departments. There are currently no available data monitoring the impact of control programs. This lack of follow-up is most likely due to political discontinuity in some areas. However, a map of the country featuring at-risk municipalities has been prepared. Vector: R. Proxilus (primary), T. dimidiata (secondary) Ecuador Disease Prevalence: Estimates of total prevalence range from 165,000 to 170,000 infected individuals [1]. Blood Supply Safety: Screening at blood banks was made mandatory in 1998; seroprevalence of donated blood is 0.2% for the entire country. Vector Prevalence and Control: The control program was reorganized in 1998, when it was placed under the Secretary of Tropical Medicine and given a budget. Vector: T. dimidiata 72

79 APPENDIX C: VECTOR CONTROL INITIATIVES Peru Disease Prevalence: Prevalence figures are fluid; numbers depend on data source and regional coverage. Estimates of total prevalence range from 600,000 to 680,000 infected individuals. Blood Supply Safety: One 1993 report estimated seroprevalence at 2.4% of total blood donations. Reports on implementation of blood screening programs for Chagas disease are contradictory. Some reports indicate that no blood donations are screened, whereas others indicate that 100% of blood donations are screened [121]. Vector Prevalence and Control: Some 394,000 homes in 4 southern departments (housing about 8% of the population) are thought to be infested. There is clear evidence of active transmission in these areas. Vector: T. infestans in Southern Peru; multiple vectors in the North include P. herreri and T. dimidiata Venezuela Disease Prevalence: The seroprevalence rate in children under 10 years of age has decreased from 20.5% in to 0.8% in 1999, and seroprevalence in 0-4 year olds has decreased to less than 1%. Estimates of total prevalence range from 414,000 to 1.1 million infected individuals. Blood Supply Safety: Seroprevalence of donated blood has decreased from 1.16% in 1993 to 0.78% in Vector Prevalence and Control: A rural housing improvement program was initiated in the 1960s and the vector control program was officially established in Vector: R. proxilus The Central American Initiative The member countries of the Central American Initiative, formed in 1997, are Belize, Costa Rica, El Salvador, Guatemala, Honduras, Mexico, Nicaragua and Panama. Belize Disease Prevalence: Seroprevalence is low in Belize: there were fewer than 700 confirmed cases in The number of infected patients has remained approximately since the 1980s. Most seropositive individuals are thought to be immigrants. Blood Supply Safety: 100% of donations are screened. Seroprevalence amongst blood donors in 2000 was 0.5% [82]. Vector Prevalence and Control: Because T. dimidiata is restricted to the wild environment, a major household eradication project has not been necessary. Vector: T. dimidiata 73

80 APPENDIX C: VECTOR CONTROL INITIATIVES Costa Rica Disease Prevalence: Estimates of total prevalence range from 78,000 to 130,000 infected individuals. Prevalence estimates have not changed much since the 1980s, when the total number of infected individuals was thought to be approximately 130,000. In 2001, a study of 7-12 year olds in one province indicated a prevalence rate of 0.2%. Blood Supply Safety: In 2000, seroprevalence amongst blood donors was 1.94%, although this study did not cover all areas of the country. Less than 10% of donated blood is screened. Vector Prevalence and Control: Chagas disease is not considered a public health problem in Costa Rica [94]. Vector: T. dimidiata El Salvador Disease Prevalence Estimates of total prevalence range from 192,000 to 321,000 infected individuals. In 2000, seroprevalence was found to be 0.3% among 7-14 year olds and 2.1% in children older than 14 years. Blood Supply Safety: Seroprevalence in blood banks was 3% in % of donated blood is screened for Chagas disease. Vector Prevalence and Control: Home infestation rate is 21% for dwellings in rural areas and in small townships. In 2000, the vector control program treated over 67% of dwellings infested with both anophelins and triatominae. Vector: T. dimidiata Guatemala Disease Prevalence: Estimates of total prevalence range from 337,000 to 734,000 infected individuals. The prevalence rate among school children in the 5 most endemic departments was 4.9% in Approximately 30,000 people are infected annually [160]. Blood Supply Safety: Approximately 75% of blood is screened. Seroprevalence of blood donations in 2000 was 0.84%, although it has been estimated to be as high as 8% in some areas [123, 124]. Vector Prevalence and Control: Home infestation rates vary from 12 to 35%. In January 2000, the Ministry of Health of Guatemala initiated a vector control program aimed at the elimination of Chagas disease transmission in 5 eastern departments. This program is being carried out in collaboration with the Japan International Cooperation Agency (JICA) and the Pan American Health Organization (PAHO), among other organizations. Vector: T. dimidiata (primary), R. prolixus (secondary) 74

81 APPENDIX C: VECTOR CONTROL INITIATIVES Honduras Disease Prevalence: Estimates of total prevalence range from 100,000 to 300,000 infected individuals. In a survey of areas under vector control, seroprevalence in children under 5 years of age was 0.36%, while that in school children 7-14 years of age was 3.3%. Blood Supply Safety: 100% of blood is screened. Seropositivity of donated blood declined from 11.6% to 1.53% between 1985 and Vector Prevalence and Control: Vector control programs exist in 6 of the 9 health regions of the country. Vector: R. prolixus and T. dimidiata Mexico Disease Prevalence: Failure to respond to endemic Chagas disease in Mexico has ramifications for the rest of the region and North America (See pg ). Despite serological surveys that have estimated Chagas prevalence in Mexico to be somewhere between 1.6 and 2.1 million people, there is little formal response to the disease. Incidence of new disease is estimated at 71,000 new cases every year, and the annual mortality due to Chagas may be anywhere between 15,000 and 62,000 people; a conservative mortality figure estimates that Chagas disease causes 25,000 deaths annually. Blood Supply Safety: Routine screening of blood supplies has not been instituted. Of some 850,000 donations, it is estimated that 12,760 units (1.5%) may be infected. Vector Control: There is no vector control program. Vector: T. barberi, others. Nicaragua Disease Prevalence: Estimates of total prevalence range from 69,000 to 176,000 infected individuals. This number is higher than the 1980 estimate of 67,000 infected individuals. In 2000, a survey of school children indicated a prevalence rate of 3.3% in this age group. Blood Supply Safety: Screening in 70% of blood banks has indicated a prevalence of 0.33% in donated blood [94]. Vector Prevalence and Control: T. dimidiata is present in 14 of 17 departments and R. prolixus is present in 5 departments. Vector: T. dimidiata and R. prolixus 75

82 APPENDIX C: VECTOR CONTROL INITIATIVES Panama Disease Prevalence: Estimates of total prevalence range widely from 6,000 to 220,000 infected individuals. The higher figure is similar to the 1980s estimate of 200,000 infected people. Blood Supply Safety: Screening in blood banks is not mandatory and less than 10% of the blood supply is screened. Vector Prevalence and Control: No compulsory vector control programs are in place. Vector: R. pallescens (primary) and T. dimidiata (secondary) 76

83 APPENDIX D: BLOOD SCREENING AND SEROPOSIVITY APPENDIX D: BLOOD SCREENING AND SEROPOSITIVITY Percent Seropositivity* of Blood Following Screening Region/ Country Status of Blood Bank Screening Southern Cone Initiative Argentina Boliva Brazil Chile Paraguay Uruguay Andean Initiative Colombia Ecuador Peru Venezuela Central American Initiative Belize Costa Rica (Derived from [11, 82, 84, 99, 150] Screening in 100% of government blood banks; 80% of private facilities Regional programs initiated, 86% screened Legislation passed, May, 1998; 100% now screened Screening in endemic areas mandatory since 1996; 91% screened Screening in all blood banks; >99% screened 100% Screening in all blood banks Screening mandatory in all blood banks since 1995; 100% screened Screening in all blood banks mandatory since 1998; 94% screened 100% screened in some areas since 2001 Screening mandatory since 1988; 100% now screened Screening in all blood banks Less than 10% of donors screened Blood Bank Seropositivity Historically (Derived from [150]) Blood Bank Seropositivity Currently (Derived from [11, 30, 42, 82, 150]) 8.7%, %, 1999 >50%, in Santa Cruz 37%, %, %, %, endemic areas 0.5%, endemic areas 11.3%, %, %, %, % % 2.4%, 1993 No transfusion transmission as of %, %, %, %, %, 1987, sample of Blood Banks 0.5%, %, 2000, sample of blood banks Screening in all blood El Salvador 2-3%, 2000 banks; 100% screened Seropositivity is an average across the country and may mask higher risks in certain areas 77

84 APPENDIX D: BLOOD SCREENING AND SEROPOSIVITY Percent Seropositivity* of Blood Following Screening (Continued) Region/ Country Status of Blood Bank Screening Central American Initiative Guatemala Honduras Nicaragua Panama Mexico (Derived from [11, 82, 84, 99, 150] ~75% now screened Screening in all blood banks, >99% now screened Screening in 70% of blood banks; 94% screened Screening not mandatory; <10% of donors screened No routine screening; Voluntary initiatives exist; national coverage Sporadic, ~15% Blood Bank Seropositivity Historically (Derived from [150]) Blood Bank Seropositivity Currently (Derived from [11, 30, 42, 82, 150]) 0.84%, 2000; 8%, est. in endemic areas 11.6%, %, 2000 Seropositivity is an average across the country and may mask higher risks in certain areas. References appear at the end of this section. 0.33% 1.5%, based on a sample of 18 govt. centers; other estimates, 0.3% % 78

85 APPENDIX D: BLOOD SCREENING AND SEROPOSIVITY Cost-Effectiveness of Blood Screening Tests 1,2 Donor Units Reagent Costs/Test Total Reagent Costs Yearly Costs per Patient Attributable to Chagas Disease (costs of medical care + lost salary) Break-even: Reagent Costs Justified if N Transmissions Prevented 4,977,000 Low: $0.25 $1,244,000 $14, N=86 High: $1.00 $4.977,000 $14, N=345 Allowance for 2-3 screens and confirmation testing: $4.00 $19,908,000 $14, N= Over-simplification excludes labor costs and the costs of technical advancements in testing technology. Medical costs may understate current cost of treatment. 2 Assumptions: a.) The relation of donor units [120, 123], reagent costs [124], medical costs [8] noted in the 1990 s is applicable in b.) Medical costs ($591.80) are incurred in year one; costs of latent disease ($174.49) are incurred for the next ten years; costs of chronic disease ($603.62) are incurred for the next 20 years. This assumes that an adult recipient of a blood transfusion lives for 31 years [8]. 79

86 Am. J. Trop. Med. Hyg., 73(5), 2005, pp Copyright 2005 by The American Society of Tropical Medicine and Hygiene APPENDIX E: MARKOV MODELS COST-EFFECTIVENESS OF CHAGAS DISEASE INTERVENTIONS IN LATIN AMERICA AND THE CARIBBEAN: MARKOV MODELS LESLIE S. WILSON,* ARTHUR M. STROSBERG, AND KIMBERLY BARRIO Departments of Medicine and Pharmacy, University of California, San Francisco, California; California Institute for OneWorld Health, San Francisco, California Abstract. Chagas disease is a parasitic disease in Latin America. Despite vector control programs that have reduced incidence by 70%, there are at least million prevalent cases. We used a Markov model to examine strategies for control and treatment of Chagas disease that compared annual costs, life expectancies, and cost-effectiveness of three vector control and drug treatment strategies. Vector control programs alone and vector control plus drug treatment are dominant over no vector control (i.e., less costly and save more lives), and vector control plus drug is highly cost-effective compared with vector control alone. We demonstrated expected changes in deaths over time resulting from various prevention approaches. Vector control affects primarily incidence, not decreasing deaths and prevalence for 30 years, while drug treatment affects prevalence and deaths immediately. The best strategy to combat Chagas disease is combinations of vector control and a potential new drug. INTRODUCTION Chagas disease is a parasitic disease found primarily in Latin America and the Caribbean. It is caused by the flagellate protozoan Trypanosoma cruzi, which is transmitted to humans by triatomine bugs primarily through posterior transmission in fecal material, by blood transfusion, and by maternal transmission. 1,2 There are many strains of T. cruzi, and antigenic differences in these strains cause geographic differences in disease pathology. Chagas disease is one of the most serious public health problems and a major cause of death in Latin America. Cross-sectional studies in the 1980s indicated that the prevalence of T. cruzi infection in the 18 disease-endemic countries of Latin America was 4.72% (16 18 million) of the population, 3 with an incidence of 700, ,000 new cases per year and approximately 45,000 deaths per year due cardiac disease caused by this parasite. 4 The current prevalence is not well documented, but is probably 3% (10 14 million cases) of the Latin American population. 5,6 However, it may be higher and is still frequently reported as million. Infection incidence now is estimated to be as high as 1.5 million/year 7 and the World Health Organization (WHO) estimates that 23,000 deaths from Chagas disease occur annually. 8 The initiation of several regional vector programs has been very successful in decreasing the incidence of Chagas disease in these regions from the 1980s to the present time. The Southern Cone initiative, which began in 1991 and accounts for almost 50% of the Latin American region, has been especially successful. The Andean and Central American initiatives begun in 1997, but have been less successful. The vector control programs in Latin America have focused on spraying of insecticides on houses and their outbuildings (usually 2 sprayings 6 12 months apart, and further evaluation and spraying of re-infested houses), combined with surveillance and education programs. These programs must be sustained and not have their priorities lowered, especially while T. cruzi infection rates are low. Chagas disease is characterized by three major stages. The * Address correspondence to Leslie S. Wilson, Departments of Medicine and Pharmacy, University of California, San Francisco, Box 0613, 3333 California Street, San Francisco, CA lwilson@itsa.ucsf.edu first is an acute stage that has clinically recognized symptoms in only approximately 1 2% of patients and is sometimes identified with a swelling around the eye known as Romana s sign or by a swelling on other parts of the body after being bitten by a triatomine. The second is an indeterminate stage in which there are no clinical symptoms and which lasts years. The third is a chronic stage in which approximately 30 40% of those infected are characterized by a non-ischemic type of cardiomyopathy with or without congestive heart failure (CHF). In addition, approximately 18 30% of patients with chronic disease have megaviscera, either megaesophagus (11 18%) or megacolon (7 22%), which results in significant morbidity and mortality. 9 Unfortunately, a large number of patients with no clinical symptoms also die suddenly primarily due to ventricular tachyarrythmias. 10 The cardiac form of Chagas disease is the main feature of chronic disease due to antigenic components of the parasite in cardiac tissue and an abnormal immune response that fails to control the infection which then leads to cellular damage and diffuse or focal chronic myocarditis with evolution of fibrosis. 11 Chagas disease cardiomyopathy is characterized by segmental wall motion abnormality. Patients with cardiomyopathy with overt CHF have mortality rates between 50% and 80% after three years. 12,13 The digestive form of Chagas disease in the chronic stage is due to denervation of the enteric nervous system that regulates the motor functions of the digestive tube, causing motility disorders primarily of the esophagus (achalasia and loss of peristalsis resulting in dysphagia) and the sigmoid colon (hypomotility resulting in constipation). Treatment is symptomatic rather than curative because the neuronal destruction is irreversible. 14 Successful regional vector control programs have been responsible for reductions of 60 99% in incidence rates of Chagas disease in parts of Latin America. 1,15 However, there are still many prevalent cases of this disease in this region and a considerable disease burden. Recent research has demonstrated that parasitic load plays a primary role in the disease, and all individuals with this disease should be treated with available drugs. 16 Current treatment is 60 70% effective only in the acute stage of this disease (defined as the disappearance of antibodies to T. cruzi). 16 However, few patients are diagnosed and treated in

87 APPENDIX E: MARKOV MODELS 902 WILSON AND OTHERS this stage. Treatment success in the chronic stage is only 8 26% with benznidazole and the same or slightly less effective with nifurtimox. Therefore, the need for additional treatments is a priority. 17 In addition, new drug treatments are needed because although vector control programs have an immediate effect on incidence of acute disease, it takes approximately years for these drugs to begin reducing the prevalence of the chronic stage, in which disease morbidity is seen and major medical treatment costs are accrued. Drugs for treatment of the large numbers of prevalent cases would be ideal and several are under early stage development. However, there is little accurate data on the costs and benefits of the various vector control and drug treatment options and none on the costs and effects of combination options such as potential new drug treatments and vector control programs. The purpose of this study was to use a Markov model to examine the costs and benefits of several current and potential strategies for the eradication and treatment of Chagas disease in Latin America and the Caribbean. METHODS We developed two types of models (Figure 1). Incidence model. We compared the costs, quality-adjusted life years (QALYs), and cost-effectiveness of a cohort of healthy newborns in 1990, assuming first that regional vector control programs had not taken place and then that regional vector control programs had been initiated in 1991 in the Southern Cone region and in 1997 in the Andean countries and in Central America. 3,4 Although there were vector control programs operational in some parts of the Southern Cone and in Venezuela in the Andean region, there was no widespread regional program until the 1991 and 1997 initiatives. Therefore, when we say no vector control in this model, we are referring to this baseline level of vector control before the regional initiatives. We compared the costs and life expectancies annually of the two cohort groups going through the Markov model and the cost-effectiveness of three potential treatment/prevention strategies: 1) vector control program alone versus no vector control program; 2) no vector control FIGURE 1. W/ with. Markov model of Chagas disease. ASR age-, sex-, and race-adjusted deaths from the life tables of Latin American countries; 81

88 APPENDIX E: MARKOV MODELS COSTS AND OUTCOMES OF CHAGAS DISEASE OVER TIME 903 program versus a vector control program plus a potential new drug treatment for Chagas disease given after the acute disease phase and having various cure rates; and 3) vector control programs alone versus vector control programs plus a potential new drug treatment given after the acute disease phase and having various cure rates. Population prevalence model. We determined the costs, QALYs, and cost-effectiveness of a prevalent Chagas disease population (adding a defined probability distribution among the starting states corresponding to Chagas disease stages) for the same three potential treatment/prevention strategies. Design. We used a steady-state Markov cohort simulation model and available literature on costs and benefits to model Chagas disease in Latin American countries with and without the benefits and costs of the vector control programs and with and without the benefits and costs of a potential new drug treatment for Chagas disease. We compared the cost and effectiveness of these different options. We discounted costs and effects by 3% to account for time preference and used 2003 US dollars. Data were analyzed with DATA Professional Software (TREEAGE Software, Inc., Williamstown, MA). We conducted sensitivity analysis to vary the cost and effect parameters in the model to see which variables were most sensitive within the model. We changed all rates to probabilities for use as transition probabilities in the model and used half-cycle corrections. Markov models consider a patient to be in one of a finite number of discrete health states. All clinically important events are modeled as transitions from one state to another using transition probabilities of moving from one state to another. 18 These models are particularly useful when determining prognosis for a medical problem that involves a risk that is ongoing over time. Each state is assigned a utility (year of life expectancy in this case), and this utility contributes to the overall prognosis by adding up the length of time spent in each state. These utilities can also be adjusted downward for losses of quality during that state. The time horizon of the analysis is divided into equal cycle lengths (one year in this case) and a transition can be made from one state to another during each cycle. Patients are absorbed into the dead state, where they remain, not being allowed to transition to another state. We analyzed using a Markov cohort simulation that considers a hypothetical cohort of patients beginning the process with some probability distribution among the starting health states. For each cycle, the patients are newly distributed among the health states according to the transition probabilities specified. At the same time, a utility (quality-adjusted life expectancy [QALE) in this case) is summed for all the states for each cycle to arrive at a cumulative utility. The simulation is run until the entire cohort is in the dead state. We have seven health states in our model: no disease, acute stage, indeterminate stage, general chronic stage, cardiomyopathy with CHF, cardiomyopathy without CHF, and two death states, one for death due to Chagas disease and one for death due to all other causes. Models. We used two types of steady-state Markov models: incidence and population prevalence. For all incidence models, we forced everyone to enter the model at the no disease state. The incidence model allows only a new born population to enter the model and run for 100 years. For the prevalence models we allowed entry into the model at all health states except death, using current prevalence figures on stage of disease and allowing incidence of disease at any age from the no disease state (prevalence models). The incidence models allow determination of disease progression alone, from well to death, including how the disease prevalence of each disease stage develops. The prevalence model allows one to see a static model of the period from 1990 to the present time and modeled into the next 100 years (excluding only migration effects and new births). This allows a more realistic estimate of Chagas disease prevalence by stage and the effects of drug treatment and vector control on them. Population. We used the WHO life tables for 191 countries to determine the population and normal population mortality by age and sex in 2000 for each of 19 countries of Latin America and the Caribbean. 19 The total population of Latin America and the Caribbean from these life tables is million (480,503,705). We allowed deaths from natural causes using the mortality from these life tables for our Markov model. Normal life expectancy in Latin America from mortality tables is years when run alone in our model. Incidence and prevalence. Disease incidence by age group, sex, and country where data was available was obtained from the report by Murray and Lopez. 20 As previously reported, the prevalence, incidence, and mortality of Chagas disease are constantly changing as a consequence of the impact of vector control programs, migration into and out of the areas, and changes in the economic conditions of the population. 1 We used the 1990 age-specific incidence estimates for the no vector control approach and estimated from the literature 1 a 70% decrease in incidence from these numbers beginning one year after the initiation date of each of the three regional vector control programs for that proportion of the total population affected by each program for our annual estimates of incidence for the with vector control approach. The agespecific incidence of Chagas disease we used in our model is shown in Table 1. The mean incidence estimates over a 100- year life time are , assuming no vector control in When we decreased these estimates by 70% at various yearly intervals starting with one year after initiation of various regional vector control programs, we used an average incidence over all ages and years of assuming vector control. We used disease and stage prevalence to determine the probability distributions of who enters each stage at the start of the prevalence models. The estimates of Moncayo 1 that we used were based on a total prevalence of 15.6 million in 1990 with no vector control, an average age at onset of 13 years, and an average disease duration of 33.7 years. His incidence estimates were 728,000 for Latin American Countries and an incidence rate overall of in 1990 with no vector control. TABLE 1 Chagas disease age-specific incidence with and without vector control Age group (years) Annual incidence with vector control Annual incidence no vector control Annual incidence high literature estimate

89 APPENDIX E: MARKOV MODELS 904 WILSON AND OTHERS Disease stages: transition probabilities. Acute disease. We allowed patients to stay only a maximum of one year in the acute stage, including both symptomatic or apparent (only 1 2% of cases) and not symptomatic or inapparent cases, and allowed a 2.5% death rate (range 0 5%) in this stage. 21 No one was allowed to return to the no disease state after having acute disease. Indeterminate stage. All cases were then forced to go into the indeterminate stage. Patients stayed a minimum of 10 years in the indeterminate stage before being allowed to progress to the chronic stage. They were also allowed to die of other causes during this stage. Some patients (40%) may remain in the indeterminate stage for life, and our model assumes that eventually everyone will move to the chronic phase with either mild or severe symptoms, and/or eventually die either of Chagas related or other causes. 22 We did not allow deaths in the indeterminate stage except from normal life table deaths from other non-chagas disease causes. Since deaths from sudden death that might occur in the indeterminate stage are often not attributed to Chagas disease, there is no data to document these deaths. The single study that tracked deaths from asymptomatic heart disease was used to account for deaths in the indeterminate stage, but they were attributed to the chronic stage (as asymptomatic heart disease; electrocardiographic [ECG] changes) because it followed the data better to model it in this way and was easier to account the exact probability of occurrence. 23 General chronic disease. As soon as symptoms or any heart changes without symptoms occur, it was assumed that a transition into the general chronic stage had occurred. Beginning at year 10 (age 10) after contracting the disease, patients entered the chronic stage at approximately 1% per year. 24 Cardiac disease. Depending on the type of symptoms, we then model increasing heart symptoms from a normal electrocardiogram and early segmental myocardial damage to some ECG changes and cardiomyopathy but no CHF, and finally to cardiomyopathy with CHF and death. The movement through the heart disease stages was based on a report by Espinosa and others. 23 Sudden deaths were assumed to occur during the asymptomatic chronic disease stage either before ECG changes or after early ECG changes. Megaviscera. Those with gastrointestinal/esophageal symptoms were moved from the general chronic disease stage to the megaviscera stage, where we assumed that approximately 20% would have palliative surgery at some point and either improve or die. Death from megaviscera was assumed to occur as a surgical or post-surgical death only (Table 2). 25 Chagas disease mortality. Patients were allowed to die of Chagas disease first in the acute stage at a rate of 2.5% (range 0 5%) and then in the chronic stage from either cardiomyopathy with or without CHF, or megaviscera. Patients were allowed to die in the sudden death cardiomyopathy without CHF stages, and also to die either suddenly or not suddenly from the cardiomyopathy with CHF stage (Table 2). Sudden death is one of the major ways of dying from Chagas disease. It is unexpected cardiac death not preceded by any apparent clinical symptoms or by symptoms less than one hour in duration. It is most often precipitated by ventricular fibrillation preceded by a few beats of tachycardia and is sometimes associated with abnormal left ventricular function resulting from cardiomyopathy. 10,26 Patients were also allowed to die in the megaviscera stage, but primarily as a result of surgical procedures to treat these diseases. Most literature seems to indicate that there are few deaths from megaviscera with the exception of a death rate of approximately 1 5% due to surgery and its sequella. 25,27 31 People were also allowed to die of non-chagas disease causes at each health state in the model using the age-specific mortality from life tables across the countries of Latin America as described earlier in this TABLE 2 Model probabilities* Probability variables Age-specific Probabilities Reference Range Annual Chagas incidence: no vector control Yes Annual Chagas incidence with vector control Yes , 20 Decrease in incidence due to vector control programs Yes 70% 1 70% and 90% Normal mortality Yes Per life table 19 Annual probability of general chronic Chagas disease No 1% 24 Annual probability of early segmental myocardial damage with no No CHF if one has chronic disease Annual probability of ECG changes and cardiomyopathy (no No CHF) if one has segmental myocardial damage Annual probability of CHF if one has cardiomyopathy No Annual probability of megaviscera if one has generalized chronic No disease Annual probability of death in acute disease stage No , 21, 22 Annual probability of death due to CHF No Annual probability of death due to cardiomyopathy without CHF No Annual probability of death due to megaviscera surgery and procedures No Assume that 20%/year have surgical procedures and death rate (from 25) Prevalence model: 1991 Prevalence of acute Chagas disease No Author estimate Prevalence of indeterminate Chagas disease No Prevalence of generalized chronic Chagas disease (no heart disease) Prevalence of CHF No Prevalence of no CHF chronic heart No * CHF congestive heart failure; ECG electrocardiogram. 83

90 APPENDIX E: MARKOV MODELS COSTS AND OUTCOMES OF CHAGAS DISEASE OVER TIME 905 report. Table 2 shows a summary of the probability variables used in the analysis. Quality adjustment of life years. We adjusted life years using disability weights averaged from two sources, and used the QALY calculations to apply them to our model. A study by Akhavan 32 in Brazil obtained disability weights that included the infected indeterminate stage as well as both mild and severe states of both cardiomyopathy and megaviscera. We averaged these rates with those provided by Murray and Lopez, 20 which gave no disability to those in the indeterminate stage and provided different rates for those who are treated (35% of the Latin American population) for their cardiomyopathy and those who are not treated. We also reversed the disability weights so that 0 death and 1 perfect health for use in adjusting life years (life expectancy [LE]) downward (LE quality adjustment) rather than for disability-adjusted life years (DALYs) (LE plus disability weighted years). This resulted in disability weights of for indeterminant stage, for those with cardiomyopathy without CHF, for those with cardiomyopathy with CHF, and 0.8 for those with megaviscera (including both mild and severe). These numbers were used as utility weights to adjust for the loss of quality of life due to time with disease when in these disease states. We did not use the additional weighting of disability for loss of life during the productive years used by Murray and Lopez in the reporting of global burden of disease because we believed that it was more equitable to weight all life years equally. 20 Disease stage prevalence. We estimated the distribution of cases among the different disease states for the prevalence Markov models by calculations using the data of Murray and Lopez. 20 (Table 2). The disease stage prevalence numbers were calculated for the whole population rather than for the Chagas disease population, unlike most of the published literature, to fit this Markov model, which is population based. We allowed these prevalent cases for each disease stage to enter the model at that stage and progress through the rest of the model. We still allowed acute cases to enter the model as new births (i.e., new acute cases beginning at age 0) as in the incidence model and also allowed an arbitrarily small number of prevalent acute cases to enter in the acute phase to complete the model. Individuals were allowed to get Chagas disease from the no disease state at any age. Direct costs. There is very little data on the use of health care and their costs for Chagas disease and most is country specific. However, the estimates of Bosombrio and others 33 from Argentina were selected for the model and are shown in Table 3. His intervention costs primarily were obtained directly from the Chagas control program of the Salta Ministry of Public Health, with some additional costs from commercial providers of certain goods and services. The value of medical services for diagnosis and supportive treatment was the average of prices charged by different clinics and hospitals in Salta, Argentina. 33 The costs were divided by disease stage. The acute phase included initial medical consultation, general laboratory tests, parasitologic and conventional serologic tests for T. cruzi infection, drug treatment with benznidazole, electrocardiograms, chest radiographs, and hepatograms. The indeterminate stage included periodic medical visits, laboratory testing, radiographs, and electrocardiograms. The chronic phase included diagnosis and supportive treatment weighted according to the prevalence of the type and severity TABLE 3 Direct (diagnosis and treatment) and indirect (work days lost) Chagas disease costs Cost variables Costs: contains both direct cost of treatment and costs of work days lost Estimated US$ Reference Annual cost of acute treatment/person $ Annual cost of indeterminate $ treatment/person Annual cost of chronic $ treatment/person Annual cost of vector programs/person $ Calculation from 22 Six month cost of drug treatment/person $100 Estimate from costs of other drugs in the market Annual cost of heart treatment/ person (averaged across prevalence and cost by disease severity) $ of symptoms. For mild cardiopathy medical consultation, electrocardiograms, chest radiographs, and intermittent antiarrhythmic drugs (such as amiodarone) were included. For severe cardiopathy a hospital admission, electrocardiograms, chest radiographs, digitalis, diuretics, vasodilators, and for some a pacemaker were included in treatment costs. For patients with megaviscera syndrome, requirements included medical visits, serologic tests, abdominal and chest radiographs, electrocardiograms, and heptograms, and for the 5% who have a surgical intervention, costs of a hemicolonectomy. 33 We excluded some costs of work days lost because we included these work losses as part of the quality of life adjustments according to the usual practice in costeffectiveness analyses. 34 We inflated the 1992 costs of Bosombrio and others 33 for Argentina to 2003 constant currency in U.S. dollars, using an average gross domestic product (GDP) implicit price deflator of all Latin American countries for U.S. dollars to account for some of the variability in monetary movement across countries. 33,35 The GDP deflator takes into account all the various price components such as fluctuating exchange rates, different purchasing power of currencies, and rate of inflation, that must be considered when converting local currencies into constant currencies. 36 Costs of vector programs. Preliminary cost estimates for the vector control programs initiated in the Southern Cone region of Latin America are $US200 million over 10 years. 22 Another study estimated that $US300 million was spent from 1991 to 2001 by the Southern Cone initiative ( Although the Southern Cone region accounts for almost 50% of the entire Latin American region, the other two regions (Andean and Central American) have more areas that require vector treatment. Therefore, although we are aware that both the method and the target across countries varies, for this estimation, we assumed that the costs of vector control would be an average of those estimates ($20 and $30 million) or $US25 million per year for each year to keep up the current vector control rates used in our model. In addition, we assumed that the other two regions would also incur a cost of $US25 million per year to continue their vector programs. This resulted in a $US 50million per year cost for complete vector control at today s success rate of 84

91 APPENDIX E: MARKOV MODELS 906 WILSON AND OTHERS a 70% decrease in incidence. When we divide this by the Latin American population, which was approximately 444 million, we get an average per person cost over the next 100 years of $0.11 per person per year with a range of $0.09 to $0.14. The vector program costs vary greatly from country to country. For example, the average cost of spraying a house in the Southern Cone region is $US In Guatemala, however, the total cost per house for spraying, labor, and transport is US$9.12, or US$48,225.7 for 5,286 houses. This is higher than in Brazil, mainly because of the higher cost of the insecticide in Guatemala. Cost of potential new drug treatment. Because the details of a new drug treatment are as yet undefined, it is difficult to assess cost. Therefore, we chose a baseline cost assuming a six-month course of treatment given one time per infected person. We determined a cost for course of treatment based on currently available treatments for Chagas disease in that region and estimates of what the market will likely be willing to pay ($100) to have a regionally acceptable cost for our base case estimates. We assumed that all patients in the indeterminate and early chronic stages would receive drug treatment. Since we also assumed that the development of tests for Chagas disease and to assess outcomes of treatment would be developed along with the development of the drug, costs and success of testing are assumed to be included in the cost of treatment and rate of cure. We did not include case detection in the model because with no accurate data we did not want the model to appear more exact than it is. RESULTS Incidence models: life expectancy and life years saved: vector control versus no vector control programs. Using the quality-adjusted base-case incidence model, we compared the current vector control program with no vector control program. We entered all patients in year 1990 at the no disease state. This allows one to see what would happen to an incident (new) population if living in a vector-controlled population, which kept vector control for the next 100 years compared with a situation without vector control over this period (Table 4). The life expectancy determined from this model was TABLE 4 Base case incidence model: life expectancy estimation with vector control and varying chagas disease incidence estimates* Annual incidence of Chagas disease Life expectancy with vector control, years No Chagas No vector control (base case) With vector control (base case) * Base case contains the most likely estimates of probabilities. years with the vector control program. This was compared with the alternative no vector control program situation modeled with incidence rates in Latin America prior to the vector programs. Again, we allowed only those with no disease to enter the model. The model indicated that these individuals had a life expectancy of years. Therefore, the current vector control initiatives save an additional 0.28 life years per person or an average of 3.4 months for each individual born in a Latin American country and entering the model in the no disease state. If there was no Chagas disease, the life expectancy using the incidence model was estimated to be years. Changes in disease incidence. Life expectancy will vary depending on the annual incidence of Chagas disease used in the model. Table 4 shows the changes in life expectancy when disease incidence varies. If the disease incidence was as high as 5% per year, life expectancy for the birth cohort would decrease to years. Compared with the life expectancy using the current base case vector controlled incidence rate (68.19), this would mean a decrease in life expectancy of 4.46 years. Cost-effectiveness of incidence models. Using the incidence model, we also compared the cost-effectiveness of both the vector control program with no vector control program and also a vector control program alone versus a vector control program plus a hypothetical new drug treatment. Tables 5, 6, and 7 show that the vector control program and the vector control program plus new drug treatment both dominate a situation with no vector control program, and that a vector control program plus drug treatment is cost-effective compared with a vector control program alone ($699/qualityadjusted life years saved [QALYS]). This cost-effectiveness of the addition of a new drug treatment is found despite that in these models we only use new incident cases and ignore the additional prevalent population that could also be treated with a new drug. Incidence models and deaths. Table 8 shows for the incidence models the changes in proportion of deaths over time with and without vector control programs and with the addition of a potential new drug that cures 50% of the cases in the indeterminate stage. Using incidence models that only track new cases of the disease, the decreases in the number of deaths after the implementation of a combination of vector control and a new drug begin after 30 years when the first Chagas disease deaths occur in the chronic stage, and then increase over time. Over a life time, the decrease in probability of deaths due to vector control and drug compared with no vector control is approximately 0.328%, with a 0.31 increase in the QALE for a single new birth going through the model (Table 8). TABLE 5 Incidence model: vector control program versus no vector control program* Strategy Cost (US$) Incremental cost (US$) Life expectancy (years) Incremental effect Incremental CE (QALYS) Vector control program $ No vector control program $165.6 $ Dominated *CE cost effectiveness; QALYS quality-adjusted life years saved. 85

92 APPENDIX E: MARKOV MODELS COSTS AND OUTCOMES OF CHAGAS DISEASE OVER TIME 907 TABLE 6 Incidence model: vector control program plus new drug with 50% cure rate versus no vector control program* Strategy Cost (US$) Incremental cost (US$) Life expectancy (years) Incremental effect Incremental CE (QALYS) Vector control program plus drug $ No vector control program $165.6 $ Dominated *CE cost effectiveness; QALYS quality-adjusted life years saved. TABLE 7 Incidence model: vector control program alone versus vector control program plus new drug with 50% cure rate* Strategy Cost (US$) Incremental cost (US$) Life expectancy (years) Incremental effect Incremental CE (QALYS) Vector control program alone $ Vector control program plus drug $58.4 $ $ *CE cost effectiveness; QALYS quality-adjusted life years saved. TABLE 8 Proportion (%) of deaths due to Chagas disease over time by type of treatment and control measures (incidence models)* Age or years passed Incidence models: no new drug No vector control Prob. of death due to Chagas Vector control Prob. of death due to Chagas Incidence models with new drug No vector control plus drug: cure 50% Prob. of death due to Chagas Vector control plus drug: cure 50% Prob. of death due to Chagas Lifetime (100) QALE * Baseline incidence is age adjusted but the average annual incidence is Discount rate is 3% per year. Prob. probability; QALE quality-adjusted life expectancy. TABLE 10 Prevalence model: cost-effectiveness (CE) vector control program plus new drug versus no vector control program* Strategy Cost (US$) Incremental cost Effect (QALY) Incremental effect Incremental CE (US$/QALYS) Vector control program plus new drug curing 50% $ No vector control program $275 $ Dominated * QALY quality-adjusted life years; QALYS quality-adjusted life years saved. Cost-effectiveness of population prevalence models. Tables 9, 10, and 11 show the cost-effectiveness of alternatives of three treatment strategies using the population prevalence models that allow the whole population of Latin American Countries to enter the model, including existing cases of Chagas disease at each stage. Strategy 1: vector control compared with no vector control. Here, we compare situations with and without vector control using a prevalence approach, i.e., allowing entrance into the model to mimic what is seen in a cross-section of the Latin American population. Our results demonstrate that the vector control program is both less costly, saves more QALYs, and dominated the no vector control program alternative (Table 9). Strategy 2: no vector control compared with vector control plus drug treatment. When we compared no vector control program with a vector control program strategy reducing incidence by 70% plus a new drug treatment program costing $100/person treated, and curing 50% at the indeterminate stage of Chagas disease, vector control plus drug also dominated the no vector control program (Table 10). Strategy 3: vector control alone compared with vector control plus new drug treatment. When we compared vector control plus the addition of a new drug that cures 50% of those with Chagas disease at the indeterminate and mild chronic stage to the current vector control strategy alone, we also had a very efficient incremental quality adjusted costeffectiveness ratio of US$289 per each additional QALYS (Table 11). The cost-effectiveness of alternative health programs or treatments internationally is determined by the gross national income (GNI) of a country and its health expenditure per TABLE 9 Prevalence model: cost-effectiveness (CE) vector control program versus no vector control program* Strategy Cost Incremental cost Effect (QALY) Incremental effect Incremental CE (US$/QALYS) Vector control program $ Vector control program plus drug $275 $ Dominated * QALY quality-adjusted life years; QALYS quality-adjusted life years saved. TABLE 11 Prevalence model: cost-effectiveness (CE) vector control program versus vector control program plus new drug* Strategy Cost (US$) Incremental cost Effect (QALY) Incremental effect Incremental CE (US$/QALYS) Vector control program alone $ Vector control program plus new drug curing 50% $229 $ $ * QALY quality-adjusted life years; QALYS quality-adjusted life years saved. 86

93 APPENDIX E: MARKOV MODELS 908 WILSON AND OTHERS capita. Given the very conservative figures used in this model for incidence, mortality, effects of both the vector control programs and the potential new drug, a GNI per capita for Latin American countries of US$3,260, and a health expenditure per capita of US$255.6 (7.0% of the GDP), all strategies are cost-effective. 38 We then further assessed the cost-effectiveness of our strategies by varying different parameter assumptions in our model using one-way and two-way sensitivity analyses for all variables, some of which are now discussed. Sensitivity analysis on cost of drug, percent cure from drug, and death rates, serologic testing, and vector control costs. We varied the additional cost of a hypothetical new drug treatment of Chagas disease to determine the break even points using the prevalence model and comparing vector control alone with vector control plus drug at the baseline incidence and for both a 50% drug cure rate and an 80% drug cure rate (Figure 2). At an additional new drug cost of up to US$100 with the prevalence model and assuming that the new drug treatment gives an 80% cure rate, the vector control plus drug strategy dominates vector control alone (being less costly and curing more lives). At US$100 the vector control plus drug treatment strategy is still cost-effective but no longer dominates, costing less than US$100/QALYS, until a drug cost of $145. Even at a new drug cost of US$300, the additional treatment is cost-effective at US$442/QALYS. If one uses the baseline case model, which assumes only a 50% cure with the new drug, the sensitivity analysis on drug cost per case (base drug cost US$100) shows that the vector control plus new drug treatment strategy dominates until a drug cost of US$45, and then has an incremental cost effectiveness ratio (ICER) less than US$100/QALYS until a drug cost of US$65, and an ICER less than US$500/QALYS until a drug cost of US$145. The ICER is still cost-effective until the US$400 maximum drug cost assessed (US$1,767/QALYS). We also conducted a sensitivity analysis on the success of the vector control program. Our base case model assumed a continued 70% decrease in incidence with the program, and we varied that to a 90% decrease in incidence. With this assumption and a prevalence model with base line new drug costs (US$100) and a 50% drug cure rate, and comparing vector control alone with vector control plus new drug treatment, the vector control plus new drug strategy no longer dominates the vector control program alone strategy but continues to be very cost-effective, costing only US$112/QALYS. When varying the cost of vector control programs from US$ 0.11 to US$1.00 per person, the vector control plus drug strategy still dominated the no vector control strategy in the prevalence model. Cases would need identification for drug treatment in the indeterminate and chronic stages of the disease and this would add additional cost to the drug treatment. Although we already tested a full range of drug costs that could include the cost of testing, we also conducted a sensitivity analysis that tested all cases that entered the prevalence model at a test cost of $3.00 per person to account for the need to test the entire population. The drug treatment plus vector control strategy still dominated the no vector control strategy in this case and up to a maximum cost of US$46 per person testing costs, where the two strategies break even for costs. We varied death rates for non-chf Chagas disease and megaviscera (both from 0 to 0.20) and for Chagas disease with CHF (0 0.80) and found that vector control programs still dominated no vector control at all probability levels. Varying the death rates similarly for the vector control alone compared with vector control plus drug strategy did not affect the outcome, varying the ICER very little and remaining costeffective. Aggregate deaths due to Chagas disease. We also calculated the proportion of the total deaths due to Chagas disease from our prevalence model (Table 12). We found that when using the prevalence model and assuming current vector control, by the age of 10 there is a 0.493% chance of death due to Chagas disease that increases to 0.938% by age 60 and to 1.04% over a life time. Both vector control alone and vector control plus drug treatment strategies showed a decreased probability of death at all ages compared with no vector control. Comparison of deaths in the incidence models (Table 8) with those in the prevalence models (Table 12) shows the variable effect as the cohort ages of the additional deaths avoided due to the addition of a potential new drug treatment when accounting for current prevalent cases compared with accounting for only new incident cases. Many deaths were avoided earlier. These comparisons demonstrate the importance of combining a drug treatment with a vector control program for the best outcomes. TABLE 12 Proportion (%) of deaths due to Chagas disease over time by type of treatment and control measures* Prevalence model Prevalence models: new drug cure 50% Vector control alone No vector control Vector control plus drug No vector control plus drug FIGURE 2. Effect on cost-effectiveness with variation in cost of drug treatment with estimated 50% and 80% cure rates (base case drug cost US$100, comparison is vector control alone versus vector control plus new drug treatment). ICER incremental costeffectiveness ratio; QALYS quality-adjusted life years saved. Years passed Prob. of death due to Chagas Prob. of death due to Chagas Prob. of death due to Chagas Prob. of death due to Chagas Lifetime QALE * Prob. probability; QALE quality-adjusted life expectancy. 87