West Nile Virus What is the West Nile virus?The West Nile virus
belongs to a group of viruses known as flaviviruses, commonly
found in Africa, West Asia, Europe, and the Middle East.
Flaviviruses are spread by insects, most often mosquitoes. Other
examples of flaviviruses include yellow fever, Japanese
encephalitis, dengue virus, and St. Louis encephalitis virus
(West Nile virus is closely related to the St. Louis
encephalitis virus). The West Nile virus can infect humans,
birds, mosquitoes, horses, and some other mammals. In 1999, the
virus occurred in the Western hemisphere for the first time,
with the first cases reported in New York City. Since then, West
Nile virus is considered an emerging infectious disease in the
US, as it has spread down the East Coast and to many Southern
and Midwestern states. West Nile virus occurs in late summer and
early fall in temperate zones, but can occur year round in
southern climates. Usually, the West Nile virus causes mild,
flu-like symptoms. However, the virus can caus