West Nile virus (WNV) is most commonly transmitted to humans by mosquitoes. You can reduce your risk of being infected with WNV by using insect repellent and wearing protective clothing to prevent mosquito bites. There are no medications to treat or vaccines to prevent WNV infection. Fortunately, most people infested with West Nile virus will have no symptoms. Almost 20% of people who are infected will develope a fever with other symptoms. Less than 1% of infected people develope a serious sometimes fatal, neurologic illness.