Epidemiology and Laboratory Capacity (ELC) - Community Resources

West Nile Virus

What is West Nile Virus?
West Nile Virus (WNV) is an arbovirus that can cause illness in humans, including encephalitis (inflammation of the brain). Mosquitos get the virus by feeding on infected birds and can then pass it on to other birds, and occasionally to other animals and people. The virus is not spread person-to-person.

An arboviral encephalitis is a viral infectious disease affecting the brain that is transmitted by a mosquito or other insect vector. The virus attacks the brain, causing inflammation and swelling. Arboviruses belong to several groups of viruses that usually infect birds and are transmitted from bird-to-bird by mosquitos. The name "ar-bo-virus" comes from the fact that they are transmitted by arthropods (insects and other "bugs").
WNV is caused by a specific type of arbovirus known as a flavivirus, which was found previously only in Africa, eastern Europe and west Asia. WNV is closely related to other arboviruses such as St. Louis Encephalitis (SLE), found in the U.S., Japanese Encephalitis, found in southeast Asia, and Murray Valley Fever, found in Australia and New Guinea.

In the U.S., WNV cases are most prevalent in late summer and early autumn; in Nevada, mosquito season is typically April through October.