National Wildlife Health Center

...advancing wildlife and ecosystem health

West Nile Virus (WNV)


West Nile Virus has spread rapidly across North America, affecting thousands of birds, horses and humans, since it was discovered in the Western hemisphere. WNV swept from the New York City region in 1999 to almost all of the continental U.S., 7 Canadian provinces, and throughout Mexico and parts of the Caribbean by 2004.

The U.S. Geological Survey is committed to understanding the effects of WNV and answering questions that surround this disease. USGS scientists are collaborating with other agencies to learn more about the ecology of WNV. The ways WNV is affecting wildlife populations, particularly wild birds, is not clearly understood. The NWHC is working on various research studies to investigate WNV in wild birds.

What is West Nile Virus?


West Nile is an insect-borne flavivirus commonly found in Africa, western Asia and the Middle East, and never reported in the Western Hemisphere before 1999. It has been detected in at least 48 species of mosquitoes, over 250 species of birds, and at least 18 mammalian species, including humans. A good way to help prevent WNV infection in humans is to avoid mosquito bites - check the CDC guidelines at the CDC West Nile Virus page

West Nile Virus Maps


USGS West Nile Virus Fact Sheets

USGS WNV resources:

Other WNV resources:

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Page Last Modified: Jan 21, 2014