Foundations of Global Health. Communicable Diseases (Part 1): Control & Smallpox Eradication. Communicable Disease Definitions.

Transcription

1 Foundations Global Health Communicable Diseases (Part 1): Control & Smallpox Eradication Learning Objectives Identify components the disease triangle and links in the chain transmission Define prevention, control, elimination, eradication and extinction for infectious diseases Identify eradication indicators Outline successful interventions against communicable diseases (smallpox) Define the International Health Regulations Identify Nationally Notifiable Diseases [When] we were beginning the global program, there was a feeling amongst scientists that you could not eradicate an organism. There was a view that organisms-- there s an ecology they fit into, in a kind way that s been around for years and years-- and to eliminate them is impossible. Nature, that lovely lady to whom eradicating malaria was failing. So to take on a second we owe polio, leprosy, smallpox, eradication program and have that fail as well would reflect syphilis, tuberculosis, cancer... very badly on the World Health Organization. ~Dr. Stanley Cohen ~Dr. DA Henderson, Director , WHO Smallpox Eradication Campaign 2 Importance Communicable Diseases Over 13 million people die each year from infectious and parasitic diseases Immensely important to the global burden disease Most important burden disease in Sub-Saharan Africa Poor people, women, children, and the elderly are the most vulnerable Enormous economic consequences Much burden unnecessary Relevance to MDGs An estimated 13.6 million died in 2008 from an infectious disease Communicable Disease Definitions 3 4 Disease Triangle Need host, pathogen & environment to produce disease Multiple external factors can influence this cycle Vectors Abiotic conditions Culture & behavior Chain Infection Model to visualize transmission a communicable disease from its source (reservoir) to a susceptible host 5 6 1

2 Pathogen Pathogen Pathogen Disease causing agent Habitat where infectious agent normally lives Human: symptomatic or asymptomatic Animal: zoonotic Non-living (environmental): plants, soil, and water contribute to life cycle Malaria Smallpox Polio HIV (top) & Tuberculosis 7 8 Exit How pathogens are passed Exit Exit Path by which an agent leaves the reservoir or source host Direct Direct contact Droplet spread Indirect Airborne Vehicleborne Vectorborne 9 10 Entry New Host Agent enters susceptible host Pathogen Exit s: Respiratory Oral Skin Intravenous Gastrointestinal Entry Exit Final link is a susceptible host Entry New Host

3 Basic Reproductive Ratio (R0) R0 definition: expected number secondary infections arising from a single individual during his or her entire infectious period, in a population susceptibles Sustained transmission Transmitting case Herd Immunity Susceptible Transmitting case Susceptible terminated Transmitting Case (A) Immune (B) Susceptible (C) (Indirectly Protected) 13 Herd Immunity Thresholds for Selected Vaccine-Preventable Diseases Disease R o Herd Immunity Immunization Levels Pre-School Months Diphtheria %* 83%* 9% Measles % 92% 96% Mumps % 92% 97% Pertussis % 83%* 97% Polio % 90% 97% Rubella % 92% 97% Smallpox % Help It s Contagious! How do we stop these diseases that can reproduce? PREVENTION CONTROL ELIMINATION ERADICATION *4 doses Modified from Epid Rev 1993;15: , Am J Prev Med 2001; 20 (4S): , MMWR 2000; 49 (SS-9); Disease Prevention Disease Control Reduction disease incidence, prevalence, morbidity or mortality to a locally acceptable level as a result deliberate efforts Need continued intervention measures to maintain control

4 Elimination Reduction to zero the incidence (new cases) disease or infection in a defined geographical area Need continued surveillance and measures to prevent re-establishment transmission Eradication & Extinction Eradication: permanent reduction to zero worldwide incidence disease or infection Intervention measures no longer needed Smallpox Extinction: infectious agent no longer exists in nature or in laboratory NONE Control Reducing infection, cases, deaths and illness due to a disease. "Acceptable" levels disease may vary by region. Consistent, sustained prevention and treatment interventions are necessary to ensure ongoing reduction illness. Elimination Reducing the number cases and new infections to zero. Efforts ten focus on a defined geographical area in which the infectious agent is endemic. Continued intervention measures are required to ensure that the infectious agent does not re-emerge in a region that has experienced elimination. The 1 st Smallpox Vaccination Jenner 1796 Cowpox lesions on the hand Sarah Nelmes (case XVI in Jenner s Inquiry), from which material was taken for the vaccination James Phipps below in 1796 Examples: diarrheal diseases, onchocerciasis (Africa), malaria, tuberculosis Examples: tetanus, poliomyelitis, leprosy, lymphatic filariasis, measles, onchocerciasis in Americas Eradication Permanent worldwide elimination an infectious agent in nature - no new infections or cases disease. The agent may exist in designated laboratories. Extinction The specific infectious agent no longer exists in nature or in the laboratory. Examples: None After a period years, intervention measures are no longer needed. Examples: Smallpox Source: CDC. 21 Smallpox Endemic Areas 1945 Smallpox Endemic Areas 1967 Endemic smallpox Endemic Importations Interrupted 4

5 R & D Contributions Smallpox Eradication Strategy Freeze-Dried Smallpox Vaccine Bifurcated Needle 98%+ take 1. Mass vaccination campaigns in each country, using vaccine ensured potency that would reach >80% population. 2. Development a system to detect and contain cases and outbreaks. Henderson DA, Moss B, Smallpox and Vaccinia in Vaccines, 3 rd edition, 1999 Mass Vaccination Surveillance and Containment Strategy Search for cases Containment spread by vaccinating primary contacts and their contacts Most efficient strategy Contacts to Contacts Contacts to Case(s) Case(s) Progression Smallpox Progression Smallpox Source: Foege, Lane, and Millar, Am J. Epi, 1969 Source: Foege, Lane, and Millar, Am J. Epi,

6 Last Cases Smallpox** Rahima Banu 16 October 1975 Variola Major-Bangladesh ** Two laboratory acquired cases occurred in UK in 1978 Ali Maow Maalin 26 October 1977 Variola Minor-Somalia Why Worry About Smallpox? 1980 Allegations that Soviet BW program produced smallpox virus for use in bombs and ICBMs Concerns that smallpox virus could be obtained and used by others as terrorist weapon JAMA 1999; 281: The Faces Smallpox Eradication: Principle Indicators Effective intervention is available to interrupt transmission the agent Practical diagnostic tools are available to detect levels infection that can lead to transmission Humans are essential for life-cycle agent no other vertebrate reservoir does not amplify in the environment 36 6

7 ITFDE Targeted six infectious diseases for eradication mumps, polio, rubella, guinea worm disease, lymphatic filariasis, and cysticercosis And, now measles! Eradication is defined as reduction the worldwide incidence a disease to zero 2010 Jones & Bartlett Publishers, LLC Adapted from CDC, Morbidity and Mortality Weekly Report 42 (1993): Candidates 38 Measles Not Now Not Possible

8 Obstacles to Elimination Non-human reservoirs Asymptomatic cases Drug resistance Weak health systems Vaccine safety concerns Autism fears Impotency Contamination 43 Control At the International Level The World Health Organization (WHO) Headquarters in Geneva, Switzerland; 193 member nations Uses sophisticated systems surveillance and communication to keep track microbial diseases on a global level Influenza surveillance network; identifies strains to include in annual vaccine Assists countries in control diseases Sets priorities and standards for disease treatment and allocation resources 2010 Jones & Bartlett Publishers, LLC 44 WHO s innovative approach to global disease surveillance International Health Regulations Only binding international agreements on disease control Framework to prevent international spread disease through effective national surveillance and coordination response to public health emergencies Maximum protection, minimum restriction IHR 1969 only applied to traditionally "quarantinable" diseases Cholera, plague, and yellow fever Restricted surveillance to info provided by governments Adapted from Grein, T.W., et al., Emerging Infectious Diseases 6 (2000): Jones & Bartlett Publishers, LLC 46 IHR 2005 More effective against global disease threats Require countries to report certain disease outbreaks and public health events to WHO Enforced in

9 National Notifiable Infectious Diseases (2007) AIDS/HIV Anthrax Arbovirus disease *California serogroup virus *Eastern equine encephalitis virus *Powassan virus *St. Louis encephalitis virus *West Nile virus *Western equine encephalitis virus Botulism Brucellosis Chancroid Chlamydia trachomatis Cholera Coccidioidomycosis Cryptosporidiosis Cyclosporiasis Diphtheria Ehrlichiosis Giardiasis Gonorrhea Haemophilus influenzae Hansen disease (leprosy) Hantavirus pulmonary syndrome Hemolytic uremic syndrome Hepatitis A, acute Hepatitis B Hepatitis C Influenza mortality Legionellosis Listeriosis Lyme disease Malaria Measles Meningococcal disease Mumps Novel influenza A virus infxn Pertussis Plague Poliovirus Psittacosis Q fever Rabies Rocky Mountain spotted fever Rubella Salmonellosis SARS-CoV disease Shiga toxin-producing Escherichia coli (STEC) Shigellosis Smallpox Streptococcal disease Syphilis Tetanus Toxic-shock syndrome (non-streptococcal) Trichinellosis Tuberculosis Tularemia Typhoid fever Staphylococcus aureus *Vancomycin-intermediate (VISA) *Vancomycin-resistant (VRSA) Varicella infection Yellow fever Practice Questions Define case, case fatality rate. What are the components the disease triangle? What are links in the chain transmission? What is the basic reproductive rate? Define prevention, control, elimination, eradication, extinction. What strategies were used to eradicate smallpox? What indicators made it possible? Define the international health regulations. What diseases were reportable under IHR 1969? IHR 2005? Name 5 nationally notifiable diseases in the United States In Summary Infectious diseases represent a major burden on public health Prevention, control and elimination are possible in significantly reducing this burden for many diseases Eradication infectious diseases are more challenging Proven success story for eradication smallpox can it be repeated? International Health Regulations and reporting notifiable diseases will aid these efforts 51 9