Prolonged periods of low rainfall are associated with more severe epidemics of West Nile virus in the United States, according to research published in Proceedings of the Royal Society B.
For the study, researchers analyzed 15 years of data on West Nile infections and weather patterns to better understand the varying intensity of West Nile epidemics in the U.S. Analysis found drought to be associated with more severe epidemics, though it was unclear how low rainfall specifically influenced the transmissibility of the virus. Researchers also found the severity of subsequent epidemics was weakened in communities where immunities were developed in the wake of an initial outbreak.
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"We show that over the next 30 years, increased drought severity from climate change could triple West Nile virus cases, but only in regions with low human immunity," wrote the study's authors. "These results illustrate how changes in drought severity can alter the transmission dynamics of vector-borne diseases."
Since its introduction to North America in 1999, West Nile has caused epidemics every summer with varying intensity. Some years the virus caused just a few hundred total illnesses, while other years brought thousands of infections. In 2002, 2003 and 2012, approximately 3,000 people suffered brain-damaging meningitis or encephalitis annually as a result of West Nile infection, according to the researchers. These epidemics resulted in the deaths of hundreds.
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