About West Nile Virus


West Nile virus (WNV) is a mosquito-borne disease first detected in the eastern U.S. in 1999. Since then, every state in the lower 48 except Maine has had human infections. Washington State had confirmed infections in birds, animals and humans in 2006, and mosquito, bird and horse cases in 2002, 2005 and 2007.

Illness and Risk

Most people experience no symptoms from the bite of a mosquito infected with West Nile virus. Twenty percent of people who become infected with WNV become ill with a mild-to-serious infection that can last for several weeks. Less than one percent (about 1 in every 150) of those who become infected develop the more serious neuroinvasive form of the disease. This can be fatal for a small number of people and sometimes leaves survivors with long-term effects such as weakness, cognitive impairment, or disability. People of all ages can become ill with West Nile virus, but people over age 50 are at higher risk. The risk of getting a severe illness increases with age.

Additional resources

Learn more about West Nile virus response at the Public Health - Seattle and King County web site or call the West Nile Virus Hotline at (206) 205-3883.

Links to Other Sites

Get more information at the Centers for Disease Control and Prevention website.