West Nile Virus

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West Nile virus (WNV) is an arbovirus that is transmitted by a bite of an infected mosquito. West Nile virus (WNV), which has been widespread in Africa, southern Europe, the Middle East and western Asia, first appeared in the New York City area of the United States in 1999. The first human cases of WNV in Wisconsin appeared in 2002. Few mosquitoes actually carry the virus.

An estimated 80% of people infected by WNV never experience symptoms. Most of the remaining 20% will experience relatively mild illness, with symptoms such as fever, headache, muscle pains, a skin rash, swollen lymph nodes, and photophobia. Less than one percent (approximately one of every 150 people) infected with WNV become seriously ill. Severe symptoms include a sudden onset of a high fever, neck stiffness, extreme muscle weakness, tremors, convulsions, or disorientation.

In nature, mosquitoes become infected with WNV by feeding on infected birds and can transmit the virus to other animals, birds, and humans. The Wisconsin Division of Public Health monitors dead birds for WNV as an early warning system to indicate that the virus may be present in an area. This information is important to heighten awareness in the prevention and control of WNV disease. People can report dead birds found near their homes to the following hotline:

Dead bird reporting hotline 800-433-1610


Wisconsin Reported WNV Disease 2002 - 2015

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Additional Info Group

Last Revised: January 19, 2018