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Including material on Evolution of Virulence (Darwinian Medicine)

Emerging Infectious Diseases. Including material on Evolution of Virulence (Darwinian Medicine). First, the good news …. Ten Great Public Health Achievements United States, 1900–1999. Source: www.cdc.gov. Vaccination Motor-vehicle safety Safer workplaces Control of infectious diseases

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Including material on Evolution of Virulence (Darwinian Medicine)

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  1. Emerging Infectious Diseases Including material onEvolution of Virulence(Darwinian Medicine)

  2. First, the good news …

  3. Ten Great Public Health Achievements United States, 1900–1999 Source: www.cdc.gov • Vaccination • Motor-vehicle safety • Safer workplaces • Control of infectious diseases • Decline in deaths from coronary heart disease and stroke • Safer and healthier foods • Healthier mothers and babies • Family planning • Fluoridation of drinking water • Recognition of tobacco use as a health hazard

  4. Now, the bad news …

  5. (1990)

  6. Source: www.who.int

  7. Reemerging Infectious Diseases • Cholera (S. America & Africa ’90s) • Dengue fever (SE Asia ’50s & Americas ’90s) • Diphtheria (Former Soviet Union ’94) • Meningococcal meningitis (esp. Africa ’90s) • Rift Valley fever (Africa) • Yellow fever (Africa & S. America) • Tuberculosis, drug-resistant (widespread)

  8. Examples of Emerging Infectious Diseases (EIDs) & Agents • Viruses • Human immunodeficiency virus (HIV) • Ebola virus • Bacteria • Legionella pneumophilia (Legionnaire’s disease) • Borrelia burgdorferi (Lyme disease) • Vibrio cholerae O139 (cholera) • Prions • Mad cow disease (BSE), vCJD, …

  9. What is a Virus? • infectious particle, composed of a protein capsule and a nucleic acid core • depends on (cells of) host organism for replication • thus, … a parasite of cells • not free living (… on borderline of life) adenovirus

  10. Causes of Disease (Re)Emergence • population explosion • global travel and migration • overcrowding and poor sanitation • mass distribution of (unsanitary) food • exposure to disease vectors and reservoirs • environmental and climatic changes (affect [insect] vectors and [animal] reservoirs) • deteriorating public health infrastructure

  11. Koch's Postulates (re: infectious diseases & agents) An organism is the cause of an infectious disease if: 1. The organism can be isolated from a host suffering from the disease. 2. The organism can be cultured in the laboratory. 3. The organism causes the same disease when introduced into another host. 4. The organism can be re-isolated from that host. … not universal. Counterexample: bacterium causing leprosy, Mycobacterium leprae, cannot be cultured in laboratory (so far), but leprosy is clearly infectious, nevertheless.

  12. Darwinian Medicine • sickle cell anemia (& malaria) • cystic fibrosis (& cholera) • fever (fights infection?) • menstruation (elimination of pathogens accompanying sperm?) … controversial field, but will likelyhave great impact on epidemiology & healthcare

  13. Hospital Superbugs • Vancomycin resistant enterococcus (VRE) • Methicillin resistant Staphylococcus aureus (MRSA) • spread by healthcare workers, diapers, etc. • problem is largely attributable to overuse of antibiotics, allowing drug-resistant pathogens to get “selected” (microevolution)

  14. Pathogen Virulence DirectTransmission Vector Transmission

  15. Paul Ewald’s “Party Line” • Pathogens do not necessarily tend towards peaceful coexistence with host — a popular medical notion called “commensalism.” • Rather pathogens can evolve towards virulence or mildness, depending largely on their mode of transmission (direct; insect vector; water; …). • Thinking in terms of evolution can provide strategies to make certain pathogens become more benign.

  16. Transmissible Spongiform Encephalopathies (TSEs) • Livestock • Scrapie (sheep) • Mad-cow disease (BSE; b=bovine) • Humans • Kuru (Fore tribe, Papua New Guinea; ritual cannibalism) • Creutzfeldt-Jakob disease (CJD) • Variant CJD (vCJD … from BSE) • Main symptoms • Ataxia and dementia

  17. TSE causative agent: the “prion” • Prion • proteinaceous infectious particle • Stanley Prusiner (Nobel Prize 1997) • lacks nucleic acids! • Resistant to radiation and heat • no immune response • gene exists on host chromosome (normal) • misfolded prion protein • propagates catalytically • PrPC PrPSc • PrP= prion protein • C = “cellular” form • Sc = “scrapie” form

  18. Neuropathology of TSEs spongiform plaques

  19. Prion Conformers PrPC PrPSc normal rogue (protease resistant form)

  20. Rogue Prion Propagation PrPSc PrPC

  21. Notice The following slides were not covered in class, as there was insufficient time. You are welcome to view them for your own interest, but you are not responsible for their content on exams etc. – E.L.

  22. Quote from Paul Ewald “When diseases have been present in human populations for many generations and still have a substantial negative impact on people’s fitness, they are likely to have infectious causes.”

  23. Example: Stomach Ulcers • Until recently, ulcers were believed to be caused by stress, diet, smoking, drugs, … • But they have now been shown to be due excess stomach acid caused by a common bacillus, Helicobacter pylori (found in stomachs of 1/3 of adults in U.S.). • Treatable with antibiotics! * Also: esophagitis, gastritis, duodenitis, achalasia, chalazia, hiatal hernia, reflux, etc.

  24. Laurie Garrett (1994)The Coming Plague : Newly Emerging Diseases in a World Out of Balance “While the human race battles itself, fighting over ever more crowded turf and scarcer resources, the advantage moves to the microbes’ court. They are our predators and they will be victorious if we, Homo sapiens, do not learn how to live in a rational global village that affords the microbes few opportunities. It's either that or we brace ourselves for the coming plague.”

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