WNV was discovered in the district of Uganda in 1937 and enzootic throughout Africa, Asia, Middle East and Europe. WNV was first appeared in North America in New York City in 1999 and has now spread across to the United States, Canada, Central America and the Caribbean (Knox). The epidemics of this infection occurred occasionally, and infection in human, horses and birds were prominent, but not severe. In August 1999, a physician noticed that many of his elderly patients suffered from encephalitis. It was thought to be St. Louis encephalitis because of the age range of the patients age, but further biological investigation revealed that it was actually WNV.
