MAJOR KILLERS OF THE PAST AND PRESENT

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1 Unit 30 MAJOR KILLERS OF THE PAST AND PRESENT LEARNING OBJECTIVES 1. Learn some information about epidemics of the past including causes, effects, and extent of these diseases. 2. Learn which epidemics of the present time have replaced those of the past, and some of the reasons for the changes. 3. Become familiar with some of the terms utilized in the field of epidemiology. INTRODUCTION There is a saying, mainly between historians, that if one doesn t remember the past he/she is bound to repeat it. It serves us well to examine the history of disease in the world. It emphasizes not only the effects it has had on the human population, but lets us know how far we have come in our understanding and control of disease. The discovery of microorganisms as causative agents of many of the epidemics was the first step toward limiting or eradiating these diseases. At the same time we should realize that elimination of organismic diseases is going to increase the deaths due to organic diseases; this of course assumes that humans have a maximum life expectancy of about 120 years. In looking at some of the major killers of the past, you must remember that there were no water treatment plants, no sewage disposal plants, no sanitation of food, and little elimination of pests (insects, rats, etc.). Once a disease producing organism entered a population, it spread widely and quickly. Epidemiology is the study of factors, events, and circumstances that influence the transmission of infectious diseases among humans. There are some common terms that are used in referring to epidemiology. Incidence refers to the number of new cases of an infectious disease that occur within a defined population (e.g. per 100,000 people) over an established period of time (monthly, quarterly, annually). Prevalence indicates the 404

2 number of active cases at any given time. A disease is considered endemic in a particular geographic area if the incidence and prevalence are expected and fairly stable. An epidemic describes an abrupt and unexpected increase in the incidence of disease over endemic rates. A pandemic refers to the spread of a disease beyond continental boundaries. The ultimate.goal of an epidemiologist is to devise strategies that interrupt or eliminate the spread of an infectious agent. To do this, infectious diseases must be classified according to: 1) incidence 2) portal of entry process by which it enters the body 3) source location from which the infectious agent was acquired 4) symptomatology signs and symptoms displayed by host during disease course 5) disease course incubation period, acute state, convalescent stage, resolution stage 6) site of infection anatomical location (where it ends, i.e. appendicitis) 7) agent cause (virulence is the ability to cause the disease and 8) host characteristics signs and symptoms. EPIDEMICS OF THE PAST. The bubonic plague (Black Death) was caused by a bacterium, Yersinia pestis (was known as Pasturella pestis),which was carried by rat fleas. The flea becomes constipated and regurgitates into the bite wound and thus the rat becomes infected. The rat dies from the disease and the flea leaves the rat and infects humans. One outbreak between killed between 17 and 28 million people; this was between 1/3 to ½ of Europe s population. The map below shows the spread of the plague (Figure 30-1). The plague was widespread during the Middle Ages because of poor sanitary conditions and the abundance of infected rat populations in areas of dense human habitation. The development of rat control programs and improved sanitation methods has greatly reduced the incidence of the disease. It is not possible to wipe it out entirely because of the large number of alternate hosts -- mice, rats, rabbits, prairie dogs and ground squirrels. Without treatment the fatality rate is 60% to 100%. Plague can be effectively treated with antibiotics. And although this disease has been mentioned as a possibility in biological warfare, it is not a good weapon for the reasons mentioned --rodents are controlled better and good sanitation in most areas plus the available antibiotic treatment in case one does become infected. Influenza (flu) is caused by a virus (Myxovirus influenzae) and it is air borne. Influenza is transmitted by inhalation of droplets containing the virus released into the air as droplets from the respiratory tract of infected individuals. It killed 22 million worldwide during the pandemic of It is still a serious disease. There was the Asian flu epidemic in It appeared in southern China early in and reached Amsterdam, Sydney, and San Francisco within weeks. This did not do anywhere near the damage of the 1918 version because epidemiologists mapped its progress, and an effective vaccine was produced. Within 10 months of detecting the first case of Asian flu, 10 million doses of vaccine had been produced. As you are aware, today flu vaccines are prepared in advance and certain groups of individuals are advised to get vaccinated. The U.S. Food and Drug Administration reports that breast-fed babies are more protected from flu than bottle-fed babies. 405

Figure 30-1. This map shows the spread of plague, the black death in the midfourteenth century. Plague was apparently introduced by seaborne rats from the Black Sea areas.

3 Figure This map shows the spread of plague, the black death in the midfourteenth century. Plague was apparently introduced by seaborne rats from the Black Sea areas. The spread of the disease generally followed trade routes from the Near East to Europe, reaching Scandinavia by 1350 and spreading perhaps as far as Iceland and Greenland, whereas areas outside the major trade routes remained virtually unaffected. (From D. Kagan, S. Ozment, and F.M. Turner, 1979, The Western Heritage, Macmillan Publishing Company, New York Smallpox (variola) is caused by a virus and once was one of the most prevalent of all diseases. The virus is very large being just slightly larger than the size of the smallest bacterium, for example Chlamydia. It is transmitted by aerosol or contact. It killed 400,000 Europeans in the 19 th century alone. 10% to 40% of its victims died and those who recovered had disfiguring pockmarks. It was noted that milkmaids, who had already been infected with cowpox, had clear skin because cowpox virus was a relatively mild infection and left no scars. On May 14, 1796, Edward Jenner, a country doctor, extracted the contents of a pustule from the arm of a milkmaid and injected it into the arm of an eight-year-old boy. It only resulted in mild symptoms in the boy. Later when he injected the boy with smallpox virus, the boy showed no symptoms of the disease. He then inoculated large numbers of his patients with cowpox; other physicians did the same. By 1800 the practice of vaccination had begun in America. 406

4 Since the advent of immunization with the vaccinia virus (believed to be a combination of the genetic material of the cowpox virus and the smallpox virus), the disease has been eradicated throughout the world. The last case of a natural infection occurred in Somalia in It is believed that the virus was kept in two locations: they are at CDC in Atlanta, Georgia and the Russian State Center for Research on Virology and Biotechnology, Koltsovo, Novosibirsk region, Russia. Some individuals believe that the Russian stock may have been distributed to other countries or agencies. Anyone born after the early 1970s, when most countries stopped vaccinating against smallpox would be completely vulnerable. And it is believed that the vaccinations given to older people would by now offer no protection. It was though that immunity from vaccination was only good for about 3-5 years. Some data collected from smallpox cases in Liverpool, England from 1902 to 1903 suggest that this is not correct (Table 30-1). Table Smallpox Cases in Liverpool, England, SEVERITY TOTAL Age Group Vaccination in Infancy Mild Moderate Severe Number of Deaths Number of cases Fatality Rate (%) > All Ages TOTAL The data suggest that even people whose vaccination was more than 50 years old received considerable protection (3.0% fatality compared to 27.2% fatality in those not vaccinated). One of the weapon of biological warfare getting much publicity is smallpox. The United States is gearing up to produce a large number of doses of vaccine. Selected groups of individuals will probably receive vaccinations (soldiers, medical personnel, etc.) If there is an outbreak, then possible contact people will receive vaccination. Figure 30-2 illustrates the difference in the spread of a disease, such as smallpox, in a population with and without immunization. 407

5 Figure Kinetics of the spread of an infectious disease and the effect of increasing the number of immune individuals in the population in limiting epidemic outbreaks of disease (A). The individuals in this population are all susceptible. The introduction of a sick individual initiates an epidemic outbreak of the disease. At the height of the epidemic, 50 percent of the population are ill. Eventually, all individuals develop the disease and are subsequently immune (B) Eighty percent of the population are immune to the disease when a sick individual enters the population. No epidemic occurs, and even a susceptible individual fails to contact and contract the disease. (from R. Atlas, Microbiology Fundamentals and Applications, 1984, Macmillan, New York.) Polio is caused by a virus and is transmitted by food and water by way of the gastrointestinal tract; and less by aerosol by way of the respiratory tract. The virus is very stable and can remain infectious for relatively long periods of time in food and water. It infected 400,000 Americans of whom 22,000 died between A Brief History of Polio taken from Microbiology 5 th ed. by Prescott, Harley and Klein is included below in Figure Since the use of the attenuated virus, Sabin vaccine (1962), the incidence of polio has decreased dramatically. There are fewer than 10 cases a year in the United States. The vaccination is still administered to children in the U.S. as a prevention in case of its introduction from other countries. In developing countries 4 or every 1,

6 children born annually have paralytic disease caused by poliovirus. The virus only enters cells that have receptors for the virus; these include the nasopharynx, gut and spinal cord anterior horn cells. Once in side the cells of the anterior horn it multiplies and destroys the cells resulting in motor and muscle paralysis. A quote from UNICEF s Polio website states Only once in human history have we witnessed the total eradication of a dreaded disease, and that was smallpox more than two decades ago. Now humanity stands on the brink of a second: the global eradication of polio. Figure A Brief History of Polio. (from Prescott, Harley and Klein, Microbiology 5 th ed.) Epidemics of the present have come about by a change in the characters but the play is somewhat the same. They are still killing millions every year and mostly in the developing countries where vaccinations, antibiotics, and medical care are still very inadequate. Table 30.2 lists the vaccinations used in the United States to prevent both viral and bacterial diseases. Figure 30-4 is the recommended immunization schedule published by the Centers for Disease Control. 409

7 Table Currently Approved Vaccines Used to Prevent Viral and Bacterial Disease in Humans. 410

Figure 30-4. Recommended immunization schedule from the Centers for Disease Control. Measles is caused by a virus that is air borne. It kills at least 1/2million annually in third world countries.

8 Figure Recommended immunization schedule from the Centers for Disease Control. Measles is caused by a virus that is air borne. It kills at least 1/2million annually in third world countries. It is the leading cause of death worldwide among vaccine preventable diseases. It has been effectively controlled in industrial nations. In 1999, the World Health Organization (WHO) and the United Nations Children s Fund (UNICEF) targeted 45 priority countries with the highest measles mortality for implementing a comprehensive strategy for accelerated and sustained measles mortality reduction. Figure 30-5 is a bar graph indicating the number of annual measles deaths worldwide for 1999 to In 1999 approximately 871,000 deaths from measles occurred with about 61% in sub-saharan Africa. This number had been reduced to about 454,000 in Table 30-3 indicates the percent of vaccinations in certain areas of the world for 1999 and 2004 and the estimated deaths for those areas in 1999 and These data indicate clearly that deaths from different preventable diseases can be reduced greatly by vaccination. 411

Figure 30-5. Estimated number of annual measles deaths worldwide, 1999 2004 (source: CDC, Progress in Reducing Global Measles Deaths, 1999 2004). Table 30-3.

9 Figure Estimated number of annual measles deaths worldwide, (source: CDC, Progress in Reducing Global Measles Deaths, ). Table Routine measles vaccination coverage and estimated number of measles deaths, by World Bank geographic region worldwide, 1999 and 2004 (source: CDC, Progress in Reducing Global Measles Deaths, ) Routine measles Routine measles Vaccination Estimated Vaccination Estimated Region Coverage (%) no. of deaths Coverage (%) no. of deaths Sub-Saharan Africa , ,000 South Asia , ,000 E. Asia and Pacific 83 68, ,000 Middle East North Africa 92 8, ,000 Europe and Central Asia 92 <1, <1,000 Latin America and Caribbean 92 <1, <1,000 High-income Countries 90 <1, <1,000 Total , ,000 Source: Progress in Reducing Global Measles Death,

10 Tuberculosis is caused by a bacterium and is air borne. Over a hundred years ago Robert Koch identified the causative agent of tuberculosis. At that time T.B. was the cause of 1/7 of all deaths in Europe. It is estimated that approximately 2 billion people are infected worldwide, with 10 million new cases each year and over 3 million deaths per year. In the United States, there are more than 26,000 cases, and 12,000 deaths reported annually. The deaths occur most commonly in the homeless, malnourished, elderly minorities, immigrants and prison populations and in Native Americans. In recent years there has been a steady increase in the number of TB cases as a result of the AIDS epidemic, and it has become a leading cause of death among people living with HIV, accounting for 13% of AIDS deaths worldwide. Recently, new multi-drug-resistant strains of tuberculosis have developed and are spreading. In Africa, Eastern Europe, and Central Asia, drug resistant strains of TB and TB/HIV co-infection threaten to undo progress made against TB. AIDS is caused by a virus that is transmitted by body fluids. This disease has been covered in the unit on STDs. Diarrhea, largely cholera, is caused by a bacterium. It has caused seven pandemics in various areas of the world, especially in Asia, the Middle East, and Africa. Figure 30-6 shows the spread of the seventh pandemic from (Taken from Brorows Textbook of Microbiology 21 Ed., Freeman, W.B. Saunders Co 1979) It is often transmitted by contaminated drinking water. It has been rare in the United States since the 1800s. It kills about 10 million annually in the third world countries. There is a vaccine for Cholera and it is recommended for individuals in endemic areas and for travelers. The diarrhea results in a severe loss of body fluid. Treatment is by replacing fluids and maintaining electrolyte balance. Treatment with antibiotics (tetracycline) generally reduces duration of the disease. Figure The global spread of cholera during the seventh pandemic, (World Health Organization) 413

11 Table Prevalence of Malaria. Malaria in Asia and the Americas Versus Africa. Asia Characteristic Americas Africa Risk of infection Very low Very high Acquired immunity No Yes Case fatality following Infection High Low due to immunity Population at risk of death All ages Infants, young children, and Women pregnant for first time History of vector control Effective Not widely applied. Source: J. Kevin Baird, Resurgent Malaria at the Millennium, Drugs, April 2000, p. 74. Malaria is caused by a protozoan. It is transmitted by the bite of the female Anopheles mosquito. It is estimated that 300 million people are infected and about 1.2 million die annually mostly in the third world countries (90% in Saharan Africa, two thirds of the remaining cases occur in six countries-india, Sri Lank, Vietnam, Colombia, and Solomon Islands). WHO forecasts a 16% growth in malaria annually. It is possible to take certain drugs which prevent the organism from multiplying in the body. Individuals going to an endemic area are advised to start taking the drug 2 weeks in advance, weekly while they are there and weekly for several weeks after returning. Resistance to chloroquine the former treatment of choice is now widespread in 80% of the 92 counties where malaria continues to be a major killer, while resistance to newer second and third-line drugs continues to grow (WHO publication CDC 2000). Figure 30-8 taken from State of the World, 2003 page 64, shows the worldwide prevalence of malaria. There has not been a successful vaccine develop although much time and money have been put in by a variety of drug companies. Figure 30-9 taken from State of the World, 2003, page 66 shows the mortality rate for malaria worldwide and Sub-Saharan Africa. Table 30-4 shows the difference in characteristics of malaria in different areas of the world. 414

12 Figure Prevalence of Malaria (State of the World, 2003, p. 64). Figure Malaria mortality rate for 1950, 1970, 1990, and 1997 (State of the World 2003, p

13 Changes in the causes of death during the 20 th century have resulted in the major causes now being organic rather than by microorganisms. We will discuss two of the major causes in other units (Cardiovascular diseases and cancer). Figure shows the causes of death in 2004 in the United States. As of 2006, AIDS has moved into fifth place. There are specific environmental causes of deaths. Table 30-5 indicates some of these from data collected in Table 30-6 lists the world cigarette production for Table 30-7 lists the annual causes of preventable deaths for the United States for Figure Causes of death in the United States in 2004 ( Table Annual deaths in the U.S. related to tobacco and other causes for Cause Number of deaths Tobacco 390,000* Alcohol 150,000 Auto accidents 49,000 Suicides 31,000 Hard drug use 30,000 Homicides 21,

14 *Table lists the world cigarette production (From Vital Signs, 2003, p. 71) Year Total Per Person (billion) (number) , , , , , , , , , , , , , , , ,541 1, , , , ,855 1, , , ,240 1, ,258 1, ,419 1, , , , , , , , , , , , (prel) 5, Source: U.S. Department of Agriculture, data for are estimates based on USDA data. 417

Table 30-7. Annual causes of preventable deaths in the United States for 2000.

15 Table Annual causes of preventable deaths in the United States for Causes Number of deaths Tobacco 435,000 Poor Diet and Physical Inactivity 365,000 Alcohol 85,000 Microbial Agents 75,000 Toxic Agents 55,000 Motor Vehicle Crashes 26,347 Adverse Reactions to Prescription Drugs 32,000 Suicide 30,622 Incidents Involving Firearms 29,000 Homicides 20,308 Sexual Behaviors 20,000 All Illicit Drug Use, Direct and Indirect 17,000 Non-Steroid Anti-Inflammatory Drugs Such As Aspirin 7,600 Source: Drug War Facts: Annual Causes of Death in the United States Figure taken from Tribune Star, Jan. 25, 2002 shows the advances that have been made against selected diseases. It indicates that in the U.S. there have been advances against a wide range of diseases and other causes of death in both Afro- Americans and Whites. There is still a significant difference between the number of deaths per 100,000 in all the categories, except suicides, with Afro-Americans having a higher rate than Whites. The Centers for Disease Control and Prevention examined the statistics for 17 key health indicators and only one did not show a decrease. The birth rate of low birth weight rose slightly from 7% in 1990 to 7.6% in Some alarming statistics based upon ethnic backgrounds were 1)Tuberculosis rates are 8 time higher in Afro-Americans and 6 times higher in Hispanics, and 2) homicides were 10 times higher for Afro-Americans and 4 times for Hispanics. Figure % decrease in death rates in 7 categories from 1990 to 1998 and the death rate per 100,000 for Afro-Americans and Whites for

16 Unit 30 OBJECTIVE QUESTIONS OVER MAJOR KILLER OF THE PAST 1. A disease that spreads beyond continental boundaries is called (A) incidence (B) endemic (C) epidemic (D) pandemic disease. 2. Incidence refers to (A) duration of a disease (B) disease course (C) number of new cases of disease within a given population (D) virulence of a disease producing organism. 3. The rat is an important organism in (A) smallpox (B) anthrax (C) bubonic plague (D) polio. 4. The causative agent of (A) smallpox (B) influenza (C) polio (D) bubonic plague (E) two of the preceding (F) three of the preceding (G) all the preceding can be transmitted by aerosol (enters by way of the respiratory tract). 5. (A) Bubonic plague (B) Smallpox (C) Polio (D) Influenza (E) Two of the preceding (F) Three of the preceding (G) All the preceding can be treated with antibiotics. 6. (A) Bubonic plague (B) Smallpox (C) Polio (D) Influenza (E) Two of the preceding (F) Three of the preceding (G) All the preceding is/are caused by a bacterium. 7. (A) Bubonic plague (B) Smallpox (C) Influenza (D) Polio is still of major concern today. 8. You should associate the name of Jenner with (A) Bubonic plague (B) Smallpox (C) Influenza (D) Polio. 9. Of the present epidemics (pandemics), (A) Measles (B) AIDS (C) Cholera (D) Malaria results in more deaths per year. 10. Match the following diseases with the type of pathogen: AIDS a. virus Cholera b. bacterium Malaria c. protozoan Measles d. insect 419

17 11. Which of the following diseases involves an insect (A) AIDS (B) Cholera (C) Malaria (D) Measles. 12. Children in the United States get vaccinated for (A) Diphtheria (B) Measles (C) Chickenpox (D) Polio (E) Whooping cough (F) two of the preceding (G) three of the preceding (H) four of the preceding (I) all the preceding 13. The main cause of death due to environmental causes is (A) Alcohol (B) Auto accidents (C) Hard drug use (D) Homicides (E) Suicides (F) Tobacco. 14. (A) Bubonic plague (B) Smallpox (C) Influenza (D) Polio is considered to have been wiped out. DISCUSSION QUESTIONS OVER MAJOR KILLER OF THE PAST 1. In comparing the causes of death in the U.S. around 1900 with the causes today, what conclusions should be drawn as the reasons for the change in the causes? 2. Examine the data about epidemics of the past and classify them as to endemic, epidemic, or pandemic. 3. Examine the data about epidemics of the past and identify the following: a. agent b. portal of entry c. source 4. What else occurred during the years of which might have played a role in the influenza outbreak? 420

18 5. What is the reason that you are not concerned about smallpox or polio? 6. The U.S. government outlaws the use of hard drugs which result in from 30,000 to 50,00 deaths a year but does not outlaw the use of tobacco and alcohol which cause 400,000 and 150,000 deaths a year respectively. Please attempt to explain the reasoning or logic behind these efforts. 7. Vigo County had 29 cases and 12 deaths from AIDS from Most people had no awareness of this. Should the public be informed and is so what is the reason(s) they are not? 8. Have we been able to develop protection against any viral disease? Explain. 421

Burton's Microbiology for the Health Sciences

Burton's Microbiology for the Health Sciences Chapter 11. Epidemiology and Public Health Chapter 11 Outline Epidemiology Interactions Among Pathogens, Hosts and the Environment Chain of Infection Reservoirs