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West Nile Virus


West Nile Virus (WNV) is a mosquito-borne disease that was first detected in the West Nile District of Uganda. Transmitted by mosquito bites, WNV affects humans, horses, some birds, and squirrels. 

In humans, it causes mild to severe flu-like symptoms such as fever, headache, body ache, and in severe cases, significant neurological symptoms or even deaths. Most people who contract the virus will have few or no symptoms and will recover completely. About 1 in 150 people who contract the disease may develop serious complications.  The elderly and those with immune system compromise are more at risk of such complications. There is currently no vaccine or specific treatment available. 

WNV in the United States
In the United States, the first WNV outbreak was reported during 1999 in New York City. The virus spread quickly across the nation during the subsequent 5 years. It was first reported in California during 2002 and in 2004 arrived in Santa Clara County.
What You Should Know 
There is no cure for WNV. Vaccines for humans are not available. People can protect themselves from WNV by taking precautions to avoid mosquito bites, and reducing or eliminating standing water on their property. 

To help us detect WNV activity, report all dead birds directly to the DEAD BIRD HOTLINE at 877-WNV-BIRD(968-2473) or online at
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Last updated: 9/28/2017 11:48 AM