West Nile Virus Encephalitis (WNV) is an infection of the brain caused by a virus transmitted by mosquitoes. WNV belongs to the same family of viruses that causes St. Louis Encephalitis (SLE). WNV was originally isolated from a febrile woman in the West Nile region of Uganda in 1937, and, since that time, has been isolated from humans, mosquitoes, and animals in Africa, southern Europe, Asia, and the Middle East. It was first found in the United States in 1999 in New York City and reached Leon County in the summer of 2001.

It is not known at this time how the virus came to the United States. Wild birds are the principal hosts of WNV. WNV has been isolated from a variety of avian species, including crows, ducks and pigeons. Birds are able to maintain a long-term infection. Consequently, migratory birds are considered to be instrumental in transporting the virus to new areas. Mammals are less important in maintaining WNV infections.

WNV infections are characterized by a bird-mosquito cycle. Transmission of WNV has two basic cycles: a rural cycle, and an urban cycle. Viral circulation most frequently begins in a rural cycle, being passed between birds (primarily wetland bird species) and bird-feeding mosquitoes. It appears to enter an urban cycle when mosquitoes that prefer to feed on both birds and humans become infected and begin to circulate the virus.

"West Nile's Sting" - 28 minute video produced by WFSU-TV/The Florida Channel for Florida Crossroads. This video requires a DSL/Cable connection or greater and is in Windows Media Player format.

For additional information about WNV and its current activity in Leon County please visit our WNV Web Site.