West Nile virus | West Nile Virus | CDC
West Nile is a virus most commonly spread to people by mosquito bites. In North America, cases of West Nile virus (WNV) occur during mosquito season, which starts in the summer and continues through fall. WNV cases have been reported in all of the continental United States. There are no vaccines to prevent or medications to treat WNV in people. Fortunately, most people infected with WNV do not have symptoms. About 1 in 5 people who are infected develop a fever and other symptoms. About 1 out of 150 infected people develop a serious, sometimes fatal, illness. You can reduce your risk of WNV by using insect repellent and wearing long-sleeved shirts and long pants to prevent mosquito bites.