The West Nile virus is a member of the family Flaviviridae, and it has become more prominent in Europe and North America in the past decade. The virus, which is closely related to the St. Louis encephalitis virus found in the United States, causes an encephalitis (swelling of the brain) in domestic animals (such as horses, dogs, cats), wild animals, and wild birds. When transferred from an infected animal to a human, the viral infection can produce encephalitis as well as inflammation of nerve cells of the spinal cord (meningitis).

In 1937, the virus was isolated from a woman in the West Nile District of Uganda. This locale was the basis for the designation of the virus as the West Nile virus. During the 1950s, the ability of the virus to cause the serious and life-threatening human disease was recognized. In the 1960s, the virus...