origins of major human infectious diseasessjryan/ppp/presentations/... · · 2008-05-02origins of...
TRANSCRIPT
Questions of interest
• Where did these major infectious diseases come from?
• Why do most of them originate from the Old World?
• How does a disease progress from existing exclusively in animal pops into human pops?
• Focus: unicellular microbial pathogens
Diseases considered in the study:
▫ 8 temperate: hepatitis B, influenza A, measles, pertussis, rotavirus A, syphiis, tetanus and TB
▫ 9 tropical: AIDS, Chagus, cholera, DHF, E. and W. African sleeping sickness, malaria, leishmaniasis
▫ 8 others: diphtheria, mumps, plague, rubella, smallpox, typhoid and typhus, tropical yellow fever
Animal pathogen human pathogen
in 5 evolutionary stages
• 1. Microbe is present in animals but not humans
• 2. Animal pathogen is transmitted to humans but not between humans (anthrax, rabies, etc)
• 3. animal pathogens have a few cycles of secondary transmission in humans but soon die out (ebola, Marburg, etc)
Prof. Durham’s ebola
• Stage 4:
▫ Disease exists in animals & humans can get infected through contact w/ the sylvatic cycle
▫ but also, the disease can be transmitted between humans w/o animal hosts
▫ Three substages:
� a) sylvatic cycle more important than direct human to human spread (Chagas disease, yellow fever)
� b) both sylvatic and direct transmission important (dengue)
� c) spread mostly through humans (typhus, influenza, cholera)
• Stage 5: pathogen is exclusive to humans
▫ Malaria, measles, mumps, rubella, smallpox and syphilis
▫ 2 ways pathogen became confined to humans:
� A)ancestral pathogen already present in the common ancestor of chimps and humans split
� B) animal pathogen recently colonized humans and evolved a separate human form
measles
Temperate/Tropical zone differences
• Greater proportion of diseases are transmitted by insect vectors in tropics than temperate zones
• Higher proportion of temperate diseases confer lasting immunity (upon survival) than in tropical regions
• Animal reservoirs are more common in tropics & an environmental reservoir is more common in temperate
• Temperate infectious diseases tend to be more acute (a few days duration) rather than chronic
• Tropical diseases are more chronic, some last weeks, months and years
• There are more stage 5 diseases in temperate zones
• There are more ‘crowd epidemic diseases’ in the temperate zones
Pathogen origins• >half of temperate diseases are from domestic animals
• Rise of agriculture helped build up crowds of people and livestock living close to each other
• Fewer tropical diseases originate from domestic animals
• Half of the tropical diseases have wild non human primate origins, compare to only one temperate
• Most diseases with animal origins are from warm-blooded animals
One exception to the last point
Geographic origins• Majority of 25 major pathogens considered originate from the Old World
▫ Historical significance in the colonization of the New World
▫ Why? : “More temperate diseases arose in the Old world than new World because far more animals that could furnish ancestral pathogens were domesticated in the Old World.”
▫ Human density: Agriculture led to higher human population densities infectious diseases thrive
Diamond is one of the authors of the paper
Future research and
steps to be taken
• 2 avenues
▫ Continue clarifying origins of existing diseases
▫ Increase surveillance for early detection of new diseases: global early warning system
Photo credits
• http://www.afip.org/Departments/infectious/mp/images/72main.jpg
• http://webs.wichita.edu/mschneegurt/biol103/lecture17/Ebola_EM.jpg
• http://katelewis.files.wordpress.com/2007/12/ebolaplush.jpg
• http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/2943.jpg
• http://weblogs.variety.com/photos/uncategorized/2007/11/18/cholera2.jpg
• http://www.skeptic.com/Merchant2/graphics/audio_video/av559_lg.jpg
• http://www.crimethinc.com/tools/downloads/preview_big/surveillance_big.gif
• The End• Thank you for staying awake!