A New Mosquito-Borne Disease in Louisiana

What is it?
West Nile Virus (WNV) is a virus disease of humans and animals that is usually transmitted by mosquitoes. Mosquitoes obtain the virus when they bite infected birds, which is where the virus is maintained in nature. WNV is closely related to St. Louis encephalitis, but it normally causes a milder disease in people.

Historical Background
Worldwide: WNV was first identified in 1937 in a woman in Africa. The earliest epidemic of WNV was reported from Israel in 1950. Since then, additional epidemics have occurred in Europe, Africa, the Middle East and North America.

United States: WNV was not known to occur in North America before 1999. It was apparently introduced into New York City during the summer of that year. By the end of 1999, there had been 25 equine (horse) cases and 62 human cases, of which seven people died. The disease has spread rather rapidly since the initial epidemic in the New York City area. In 2000, there were another 21 human cases from three northeastern states and 60 more equine cases from seven northeastern states. WNV positive birds were reported in 13 states, the southernmost being North Carolina. In 2001, WNV spread throughout most of the eastern half of the United States. WNV positive birds were reported from 28 states. There were 738 equine cases in 20 states and 66 human cases in 10 states. Southeastern states that reported human WNV cases were Florida, Georgia, Alabama and Louisiana. The continued expansion of WNV suggests that it is firmly established in the United States.

Louisiana: WNV spread from New York to Louisiana much faster than originally predicted. The first sign of the disease was a WNV-positive blue jay reported in July of 2001. Afterward, there were nine equine cases from four southern parishes and one human case in Jefferson Parish (New Orleans area). As of April 1, there had already been one equine case and one positive bird reported in 2002. WNV is expected to remain-in Louisiana.

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