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West Nile Virus Overview

West Nile Virus Cases

The West Nile virus first emerged in Uganda's West Nile region in 1937. The disease then turned up in Africa, Eastern Europe, West Asia and the Middle East. The first West Nile cases in the United States were discovered during the summer of 1999. In that year, the disease infected 62 people and killed seven in the New York area. By the following year, the West Nile virus had spread up and down the East Coast from Vermont to North Carolina. In 2002, it had reached all the way to Texas. As of 2004, it had spread through all 48 U.S. mainland states, as well as into Canada and throughout Mexico.

Photo courtesy Centers for Disease Control
Worldwide geographic representation of occurrence
of West Nile virus

An estimated 16,000 people in the United States have become ill from West Nile virus since 1999, and more than 600 have died. A far greater number of people have probably been infected without knowing it because they did not have any symptoms. Outside of North America, regular outbreaks also occur in Africa, Europe, and Asia. In 1996-97, for example, an outbreak near Bucharest, Romania, infected more than 500 people and killed about 50. There are no valid statistics on the number of people infected worldwide.

U.S. West Nile Cases*
Year Number of Cases Number of Deaths States with Highest Numbers of West Nile Cases
1999 62 7 New York (62)
2000 18 1 New York (14), New Jersey (4)
2001 66 9 New York (15), New Jersey (12), Florida (12)
2002 4,156 284 Illinois (884), Michigan (614), Ohio (441), Texas (202)
2003 9,862 264 Colorado (2,947), Nebraska (1,942), South Dakota (1,039), Texas (720), North Dakota (617)
2004 2,470 88 California (771), Arizona (391), Colorado (276), Texas (158)
*Source: U.S. Centers for Disease Control (CDC)

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