What Is West Nile Virus?
West Nile virus (WNV) is an emerging infectious disease that made its first appearance in the United States in 1999. The microbe that causes the infection belongs to a group of disease-causing viruses known as flaviviruses that are usually spread by ticks or mosquitoes. Other well-known diseases caused by flaviviruses include yellow fever, Japanese encephalitis, dengue, and Saint Louis encephalitis.
History
WNV was first isolated in Uganda in 1937. Today it is most commonly found in Africa, West Asia, Europe, and the Middle East. In 1999, it was found in the Western Hemisphere for the first time in the New York City area. In early spring 2000, it appeared again in birds and mosquitoes and then spread to other parts of the eastern United States. By 2004, the virus had been found in birds and mosquitoes in every state except Alaska and Hawaii.
In 2007, WNV caused 3,404 cases of disease in the United States, including 98 deaths, according to the Centers for Disease Control and Prevention (CDC). Human cases have now been reported throughout the continental United States and in Canada and Mexico.
Visit the CDC Web site for the most recent numbers of reported human cases of WNV infection in the United States.