Researchers from Oregon State University and the University of Florida have identified how those factors mesh to create heightened risk of the West Nile Virus in southern Florida, and they hope to expand their studies to the rest of the nation.

Results of the research have been published by the Centers for Disease Control.

Many early hydrologic models predicting the transmission of West Nile Virus and other mosquito-borne diseases may have been a bit too simplistic, relying on factors such as total rainfall to estimate disease risk, said Jeffrey Shaman, an assistant professor of atmospheric sciences at Oregon State University. The situation, he adds, is much more complex.

"In some cases, rain can actually help control mosquitoes by flushing away larval habitats," Shaman said. "And simply having more mosquitoes doesn't necessarily mean that we'll experience a greater incidence of West Nile Virus. The mosquitoes themselves must first be infected with the virus. Researchers call the process through which more mosquitoes become infected 'amplification,' and there are a number of factors that lead to that stage.

"By identifying these factors in the wild, it will enhance our ability to create control strategies."

In their studies, Shaman and colleague Jonathan F. Day from the University of Florida found that spring drought followed by continual summer rainfall is critical for the amplification and transmission of West Nile Virus and a similar disease, St. Louis Encephalitis Virus, in southern Florida. When drought occurs early in the year, the limited water resources confine mosquito populations to selected habitats specifically isolated, densely vegetated hammocks where conditions remain humid.
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Contact: Jeff Shaman
jshaman@coas.oregonstate.edu
541-737-4915
Oregon State University
4-May-2006