Prev NEXT  


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)

To find out more about West Nile virus and related topics, check out the links on the next page.

Related HowStuffWorks Articles

More Great Links


  • "West Nile Virus: Epidemics Deadly Diseases Throughout History" by Phillip Margulies
  • "West Nile Story" by Dickson Despommier
  • ">West Nile Virus" by Melissa Abramovitz
  • "West Nile Virus" by Jeff Sfakianos


  • Brown, Anthony J. "West Nile Vaccine Making Progress." Reuters Health, May 11, 2005.
  • CDC, "West Nile Virus."
  • "CDC Adopts New Repellent Guidance for Upcoming Mosquito Season," CDC Press Release. April 28, 2005.
  • "NIAID Begins Clinical Trial of West Nile Virus Vaccine." NIH Press Release, April 18, 2005.
  • NIAID, "NIAID Research on West Nile Virus."
  • NBII, "West Nile Virus."
  • "Official: West Nile Vaccine Promising." Associated Press, May 11, 2005.
  • "Promising New West Nile Therapy Cures Disease in Mice." NIH Press Release, April 24, 2005.
  • West Nile Virus. Mayo Clinic.