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The Biogeography of Infectious Diseases One of the consequences of the domestication of plants and animals and the resultant increase in human populations was the increased importance of infectious diseases. There were two basic reasons for this: 1) the increased density of human populations, and 2) the transmission of infectious diseases to people from their domesticated animals (See Jared Diamond’s “Guns. Germs and Steel” for a discussion of this theme). Below is his listing of “Deadly Gifts from our Animal Friends.” Measles Tuberculosis Smallpox Flu Pertussis Falciparum malaria Cattle Cattle Cattle Pigs and Ducks Pigs and Dogs Birds (Chickens and Ducks) How do infectious diseases spread through a population? The spread of an infectious disease though a population can be thought of as a wave like phenomenon. The graphs on the next two pages show how this works. Note that the term “epidemic” in medical geography means “always present in the population.” Two Examples of Infectious Disease • The Plague • Influenza The Plague This disease involves interactions between several species. The Vector: Xenopsylla cheopsis The Agent: Yersinia pestis a bacterium The Host: Rattus rattus – the Black Rat There have been three major outbreaks (pandemics) during the last 2,000 years. The population of Western Europe PATTERSON, K. DAVID, The Geography and Mortality of the 1918 Influenza Pandemic , Bulletin of the History of Medicine, 65:1 (1991:Spring) pp.4-21 25-40 million people died My grandmother died of the flu in 1918. For a model that shows the spread of a flu epidemic throughout the US click here and start the movie: http://www.nigms.nih.gov/News/Results/Flu Model040306.htm For a general summary of what the model does click here: http://publications.nigms.nih.gov/Multimedi a/Video/vaccine-19.html The details behind the model are published in the following (very technical) journal article. For a copy click here: http://www.pnas.org cgi doi 10.1073 pnas .0601266103 Germann et al. PNAS April 11, 2006 vol. 103 no. 15 5937