The West Nile virus is a mosquito-borne infection. Infected mosquitoes can spread the virus to humans and other animals. West Nile virus is usually spread by the bite of a mosquito that has fed on an infected bird. Most people who get West Nile virus experience no symptoms or only mild flu-like symptoms, but it can cause serious illness and there are few medical options to treat or prevent it.
Anyone can become infected if they are exposed to a mosquito bite. It only takes a single bite from an infected mosquito to contract West Nile virus. The risk of WNV varies from year to year based on precipitation, temperature, and mosquito populations. The highest risk periods are generally when mosquito populations are at their peak during the summer months. Individuals spending time outdoors are greater risk of exposure.