Common Infectious Disease


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a brief outline of some of the scarier infectious diseases disproportionately affecting populations worldwide

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Common Infectious Disease

  1. 1. Infectious Disease Transmission in Tropical Environments Mary Dain ESPM 194 Spring 2007
  2. 2. Worldwide Infectious Disease World Health Organization at
  3. 3. What is an infectious disease? <ul><li>American Heritage Stedman's Medical Dictionary - infectious disease ( n.) </li></ul><ul><ul><li>A disease resulting from the presence and activity of a pathogenic microbial agent. </li></ul></ul><ul><li>Four main types of infectious disease carrying-pathogens: bacteria, viruses, protozoa, and helminths </li></ul>
  4. 4. Bacteria <ul><li>single-celled, free-living, ubiquitous prokaryotes </li></ul><ul><li>Such as tuberculosis, salmonella, cholera, leprosy, plague </li></ul>Illinois Department of Health:
  5. 5. Viruses <ul><li>Parasitic, eukaryotic </li></ul><ul><li>Such as measles, smallpox, hepatitis, HIV </li></ul>Scientific American, 1995. At:
  6. 6. Protozoa <ul><li>Single-celled, no cell walls, larger than bacteria and more complex, frequently use vectors </li></ul><ul><li>Such as malaria, leishmania, giardia </li></ul>Helveticum Instituticum Tropologicum, at:
  7. 7. Helminth <ul><li>Multi-cellular worms, free-living or parasitic </li></ul><ul><li>Such as schistosomiasis, guinea worm, hookworm </li></ul>CDC Public Health Image Library
  8. 8. Communicable Diseases in the Environment <ul><li>Most common in developing countries, particularly in warmer climates </li></ul><ul><li>Still very prevalent: under-5 child mortality rate is 168 for every 1,000 live births in Sub-Saharan Africa (source: World Bank, HNP statistics 2004) </li></ul><ul><li>The environment has direct impacts on the transmission of almost all communicable diseases in the developing world </li></ul>
  9. 9. Transmission <ul><li>All infectious diseases transfer themselves along one of the following routes: </li></ul><ul><ul><li>Fecal/oral </li></ul></ul><ul><ul><li>Respiratory </li></ul></ul><ul><ul><li>Blood borne/sexual </li></ul></ul><ul><ul><li>By contact </li></ul></ul>
  10. 10. Water-borne Diseases
  11. 11. Cholera <ul><li>Commonly known for pandemics in England (1817) and New York city (1830’s) </li></ul><ul><li>Yet still very common today – there were 100,000 cases of cholera worldwide in 2004, causing 2,300 deaths in 56 different countries </li></ul>
  12. 12. Cholera’s habits <ul><li>Water-borne bacterium ( Vibrio cholera ) </li></ul><ul><li>Seasonal: warm weather promotes growth </li></ul><ul><li>Forms bacterial reservoirs in brackish waters </li></ul>Photo curteosy of Sudan Watch blog:
  13. 13. What it does: <ul><li>Alters activity of G proteins in intestinal cells, so that they become “stuck” in an activated state, pumping water continuously out of cells and into the intestines </li></ul><ul><li>Severe diarrhea and dehydration result </li></ul>Dr. Wim Hol, U Washington at:
  14. 14. This results in: <ul><li>Loss of 20 liters of water/day over 5 to 8 days </li></ul><ul><li>Shock and/or death </li></ul><ul><li>Bacteria exits the body in feces, contaminates local drinking water and the cycle continues </li></ul><ul><li>Most commonly occurs in children, afterwards develop base immunity </li></ul>
  15. 15. Human Defenses <ul><li>Malnourishment, parasitic infection contribute to likelihood of contracting cholera </li></ul><ul><li>First-infection can produce long-term immunity </li></ul><ul><li>Endemic area resistance </li></ul>
  16. 16. The Future of Cholera <ul><li>Global case-fatality down 47% from 1961 </li></ul><ul><li>Oral Rehydration Therapy: glucose, potassium, salt </li></ul><ul><li>Evolving pathogen </li></ul><ul><li>Improved coordination of relief efforts </li></ul><ul><li>Improved sanitation systems </li></ul>
  17. 17. Schistosomiasis <ul><li>Water-borne helminth with a complex life-cycle </li></ul><ul><li>Dependent upon one genus of snail ( Biomphalaria spp. ) to survive </li></ul>
  18. 18. Transmission <ul><li>Takes the form of cercariae that carry out part of lifecycle in water, in snails, and in a human host as worms </li></ul><ul><li>Enters the body through the skin, in water contaminated with cercariae </li></ul>Shistosomiasis Forum, Human Diseases and Conditions, at:
  19. 19. CDC:
  20. 20. Effects <ul><li>Acute symptoms: Lethargy, fever, liver damage </li></ul><ul><li>Chronic symptoms: distended belly, cirrhosis of the liver/colon </li></ul>
  21. 21. Blood in Urine
  22. 22. Infection Process <ul><li>Shistosome eggs are laid in feces, and hatch when they reach fresh water </li></ul><ul><li>Common to find shistosomiasis in freshwater sources around the globe, particularly large pools or slow-moving water </li></ul><ul><li>Any person in the water is at risk of infection </li></ul>
  23. 23. Remediation <ul><li>Cercariae removal not really possible </li></ul><ul><li>Snail populations are too hardy to be eliminated </li></ul><ul><li>Base education about the presence of snails </li></ul><ul><li>Boot-wearing </li></ul><ul><li>Septic tank systems, water purification </li></ul>
  24. 24. Dam-Building <ul><li>Reservoirs create a snail habitat </li></ul><ul><li>Can create a bridge between endemic areas </li></ul><ul><li>If reservoir is infiltrated, Yangtze river could become breeding ground for shistosomes after the building of the Three Gorges Dam </li></ul>
  25. 25. Future of Schistosomiasis <ul><li>Ending dam-building will hinder snail population growth </li></ul><ul><li>Large-scale irrigation projects must be checked to avoid circariae breeding grounds </li></ul><ul><li>New drug: praziquantel is effective way to treat symptoms, stop human egg-shedding </li></ul><ul><li>Vaccine in 10-20 years </li></ul>
  26. 26. Guinea Worm <ul><li>Water-borne helminth that lives out a very long portion of its lifecycle inside the human host </li></ul><ul><li>Has seen a major reduction in recent years, down from 3.5 million cases in 1986 to 16,000 in 2004 </li></ul>
  27. 27. Guinea Worm Lifecycle
  28. 28. Problem: Communal Water Source <ul><li>Blisters that form are very painful, requiring the victim to submerge the affected limb in water, releasing more larvae </li></ul><ul><li>The importance of waste water treatment and clean water management cannot be overstated </li></ul>
  29. 29. Eradication is on the Horizon <ul><li>Three-quarters of the remaining cases of Guinea Worm exist in Southern Sudan </li></ul><ul><li>1995 Jimmy Carter Guinea Worm cease-fire </li></ul><ul><li>Recent success stories </li></ul> , with permission published by
  30. 30. Respiratory Infections
  31. 31. The Big Respiratory Threat of 2007: Tuberculosis <ul><li>Mycobacterium tuberculosis </li></ul><ul><li>Leading cause of death among young adults worldwide – 2 billion people are currently infected, 300,000 of them are drug resistant </li></ul><ul><li>Commonly associated with slums, poverty, and high population density </li></ul><ul><li>Transmitted through the respiratory route </li></ul>
  32. 32. What it Does: <ul><li>TB enters the lung </li></ul><ul><li>Gets encased in macrophages, forms a tubercle, which prevents spreading </li></ul><ul><li>Remains as such for years </li></ul><ul><li>When immune system is compromised, tubercle melts and TB comes out and multiplies </li></ul>
  33. 33. Tuberculosis at large <ul><li>Symptoms: cough, chest pain, fever, weakness, dramatic weight loss </li></ul> <ul><li>Very infectious, but only 5-10% of healthy people infected with TB develop the disease </li></ul>
  34. 34. <ul><li>80% of TB cases are in 22 underdeveloped countries </li></ul><ul><li>TB is the number one killer of HIV infected people, prevalance of co-infection is highest in Africa </li></ul>
  35. 36. MDR-TB <ul><li>4 medications are used widely to treat TB </li></ul><ul><li>Inexpensive, but must be taken regularly for six to eight months </li></ul><ul><li>Skipping any dose causes MTB to mutate </li></ul><ul><li>80% of all cases of MDR-TB are superstrains, so they are resistant to at least 3 out of 4 drugs used to treat the disease </li></ul>
  36. 37. DOTS <ul><li>World Health Organization’s “Directly Observed Treatment” </li></ul><ul><li>DOTS campaigns have yielded 85 - 100% cure rates in many clinics </li></ul><ul><ul><li>90% in studies in Peru; 100% in Haitian sites </li></ul></ul><ul><li>BUT today, less than 25% of TB patients worldwide are treated with DOTS Strategy </li></ul><ul><li>25% of TB infected have no access to DOTS </li></ul>
  37. 38. The Future of Tuberculosis <ul><li>“ Tuberculosis has not reemerged, it has reemerged from the poor.” –Dr. Paul Farmer </li></ul>
  38. 39. Malaria <ul><li>Water-related, vector-borne, world’s number one parasitic disease </li></ul><ul><li>300 – 500 million infections per year </li></ul><ul><li>1-3 million deaths per year, 90% are African </li></ul><ul><ul><li>3,000 child deaths per day (WHO, 2002) </li></ul></ul>
  39. 40. Effects <ul><li>Transmitted mostly from mosquito bites, also from blood transfusions, mother/child transmission, organ transplant </li></ul><ul><li>Symptoms: flu, fever, chills, mouth sores, loss of consciousness, death </li></ul>
  40. 41. Four types, Two hosts <ul><li>Four species of parasite that can infect humans </li></ul><ul><li>There are 400 species of Anopheles mosquitoes, 30 of them carry malaria </li></ul>
  41. 42. Encarta pictures at:
  42. 43. Treatment <ul><li>Acquired immunity over time </li></ul><ul><li>Chloroquin, quinine, mefloquin </li></ul><ul><li>Difficult to treat because it has a large genome, and rapidly mutates </li></ul><ul><li>Prevalance increases with population density, incidence of standing water </li></ul>Time Magazine image:
  43. 44. Human behavior Affects Transmission <ul><li>Creation of mosquito breeding sites: irrigation ditches, water buckets, puddles </li></ul><ul><li>Deforestation decreases resting sights for mosquitoes </li></ul><ul><li>Mass migrations (India/Pakistan border) </li></ul><ul><li>Agricultural work </li></ul><ul><li>Raising livestock near house </li></ul><ul><li>Bed-net use </li></ul>
  44. 45. Malaria Remediation Efforts <ul><li>Insecticide-treated bed nets </li></ul><ul><li>Introduction of mosquito-eating fish </li></ul><ul><li>Filling or covering pits, puddles </li></ul><ul><li>Pesticide use for indoor and outdoor spraying </li></ul>
  45. 46. DDT <ul><li>Persistant Organic Pollutant, phased out in POPs treaty of 2001 </li></ul><ul><li>Persists in the environment </li></ul><ul><li>Bioaccumulates </li></ul><ul><li>Travels long distances </li></ul><ul><li>Toxic to wildlife </li></ul><ul><li>Can cause premature birth in humans </li></ul><ul><li>Some mosquitoes develop resistance to it </li></ul>
  46. 47. <ul><li>BUT, indoor DDT use reduces malaria transmission by 90% </li></ul><ul><li>Ten countries in Sub-Saharan Africa still use it </li></ul>
  47. 48. One More Factor in Infectious Disease Prevalence <ul><li>Most infectious disease victims are suffering already from a host of other problems </li></ul><ul><li>Most commonly: malnutrition </li></ul>
  48. 49. Conclusions <ul><li>In the face of global climate change, warm places will only be getting warmer, and therefore facing more exposure </li></ul><ul><li>In the face of globalization and development, public health workers, environmental scientists, and public policy workers have to work together in order to decrease mortality rates and increase health expenditures in developing countries </li></ul>
  49. 50. Source Material <ul><li>infectious disease. (n.d.). The American Heritage® Stedman's Medical Dictionary . Retrieved February 24, 2007, from website: http:// /browse/infectious disease </li></ul><ul><li>Onchocerciasis volvalae at: </li></ul><ul><li>WHO communicable diseases: http:// /infectious-disease-news/ </li></ul><ul><li>-neglected tropical diseases: http:// / </li></ul><ul><li>World Bank Health and Population Data, including vital statistics:,,menuPK:282516~pagePK:149018~piPK:149093~theSitePK:282511,00.html </li></ul><ul><li>Center for Disease Control and Prevention. Department of Health and Human Services. [Online] Available at : </li></ul><ul><li>Image sources: </li></ul><ul><li>Water-borne disease image: </li></ul><ul><li>Hookworm image: http:// </li></ul><ul><li>G protein activation graph: http:// </li></ul><ul><li>The defenders image: http:// </li></ul><ul><li>Imperial College of London blood in urine image: </li></ul><ul><li>Schistosomiasis life cycle graph, CDC: CDC: </li></ul><ul><li>Yangtze farmer: http:// =y </li></ul><ul><li>Three gorges dam: </li></ul><ul><li>east African river: </li></ul><ul><li>guinea worm extraction photo: </li></ul><ul><li>Malaria woman and child: </li></ul><ul><li>DDT: </li></ul><ul><li>DDR jar: http :// / decada / ddt.jpg </li></ul>