West Nile Virus

What is West Nile Virus?

West Nile virus (WNV) is a mosquito-borne virus of birds that also causes illness and death in horses and humans. West Nile virus was first identified in the United States in 1999 in New York City and subsequently spread to all 48 contiguous states by 2004. Transmission is seasonal with the majority of cases in Wyoming occurring in the late summer.

How Does West Nile Virus Affect Me?

West Nile virus can cause serious, life-altering, and even fatal disease in humans. Precautions should be taken to avoid being bitten by mosquitoes particularly during the peak transmission periods of late August and early September. Humans can also be infected when conducting necropsies on infected birds. Most humans infected with the virus develop inapparent infections. Clinically-ill people develop either West Nile Fever or the more severe WNV encephalitis. Clinical symptoms of West Nile Fever are usually mild and include fever, headache, body aches, and in some cases, skin rash and swollen lymph nodes. Clinical signs of WNV encephalitis include high fever, stiff neck, muscle weakness, convulsions, and paralysis. Death rates associated with severe WNV infection range from 3–15% and are highest among the elderly.

Impacts of West Nile Virus on Wildlife

West Nile virus infection can cause significant mortality in avian species such as crows, jays, magpies, hawks, owls, and eagles. Sage grouse are particularly susceptible to WNV infection and significant mortality events have occurred in the Powder River Basin of Wyoming. West Nile virus does not typically cause morbidity or mortality in big game animals in Wyoming, but mountain goats may be acutely susceptible.

West Nile Virus Reports

Useful websites for further information about WNV.

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