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West Nile Virus

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Culex tarsalis mosquito, which transmits West Nile virus
Close-up anterior view of a Culex tarsalis mosquito about to begin feeding on a human host.
Credit: CDC

West Nile virus (WNV) first emerged in the Western Hemisphere in 1999 in the New York City area and has since spread across the United States. The virus is transmitted to humans by mosquitoes.

Most human infections are mild, causing fever, headache, and body aches, often accompanied by a skin rash and swollen lymph glands. If the virus crosses the blood-brain barrier, however, it can cause life-threatening conditions that include inflammation of the brain and spinal cord.

NIAID supports research on West Nile virus through its comprehensive emerging infectious disease program. This program supports research on bacterial, viral, and other types of disease-causing microbes.

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Last Updated July 06, 2015