West Nile

West Nile emerged in 1937 in Africa and first appeared in North America in 1999 in New York. Similar to the other encephalitis, it is cycled between birds and mosquitoes and transmitted to mammals including horses and man by infected mosquitoes. Over 36 species of mosquitoes have tested positive for WN virus, the Culex pipiens pipiens complex seems to be the most common species associated with human and horse cases. In 2006, there were 4,256 human cases in the United States. Three human cases were reported in Florida.