After geographical analysis in Sverdlovsk showed the cases to be tightly clustered in a linear plume southeast of the city, meteorological analysis pinpointed the date of exposure to 2 April 1979.44 In addition, wind direction, rainfall, and temperature history are all useful clues as to whether or not a disease would likely occur naturally. Climate influences infectious disease patterns because pathogens and their vectors are sensitive to temperature, rainfall, and other ambient conditions. This is shown by the characteristic geographic distribution and seasonal variation of many infectious diseases. Mosquito-vectored diseases, such as Dengue, malaria, and West Nile fever are seen primarily during warm periods; influenza increases in cool weather; meningitis is associated with dry environments; and cryptosporidiosis is associated with heavy rainfall.71 Wind direction and speed also influence the pattern of disease spread, as noted at Sverdlovsk and in foot-and-mouth disease outbreaks.
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