West Nile virus has been identified in five American crows from the St. Louis area. The U.S. Geological Survey National Wildlife Health Center has notified the Missouri Department of Health that the crows tested positive. To date, no laboratory-confirmed human cases of West Nile virus have been reported. The virus is transmitted by mosquitoes. Most people infected with the virus do not develop any symptoms. Sometimes, though, mild illness results one to to weeks after exposure with symptoms such as fever, headache, body aches, skin rash, and swollen lymph nodes. Less than one percent of infected people develop a serious illness.