How do I know if an animal is infected with West Nile Virus?

Signs of infection in wildlife, like in humans, can range from no symptoms to severe symptoms of neurologic illness. Commonly reported signs in animals include weakness, stumbling, trembling, head tremors, inability to fly/walk, and a lack of awareness that allows them to be easily approached and handled. These symptoms, however, can also have other causes. The only way to positively confirm West Nile Virus infection is by laboratory testing of the animal’s tissues.

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Photograph of a person conducting mosquito sampling on a boardwalk
2016 (approx.)

Researchers dip sampling for mosquitoes along the Alaka‘i Swamp Trail, Kaua‘i

Photograph of female mosquito (Aedes japonicus)
2016 (approx.)

A female mosquito (Aedes japonicus) reared from larvae collected from the Kawaikoi Stream, Kauai.

Researcher working in the laboratory
July 14, 2016

Researcher working in the laboratory.

Mosquito trap
May 16, 2016
Image: Biting Mosquito
March 14, 2016

Culex species mosquito biting a human hand.

Image: USGS Scientist Set Mistnets for West Nile Virus Monitoring
February 8, 2005

USGS scientists capture and release wild birds while monitoring for West Nile.

Mosquito, Aedes aegypti

Mosquito, Aedes aegypti

Image: Curlews Caught by Mist Nets

Curlews are very attentive parents and fly close to intruders and alarm call to distract them from their young broods. USGS scientists take advantage of this behavior by using a mist net to sweep birds out of the air when they approach. In June 2007, USGS scientists used this approach to tag 13 curlews with satellite transmitters at their southern breeding area in Alaska. They use satellite telemetry to track these birds, in order to map their migration routes and find the location of their nonbreeding areas.