Since 1999, West Nile virus has spread throughout the U.S., frequently sickening and occasionally killing people. The virus has killed at least one person in every state in the conterminous U.S. “There are many risk factors for infection with West Nile virus,” says U.S. Forest Service research forester Wayne Zipperer. “However, risk factors are complicated and not well understood.”
Mosquitoes, such as this southern house mosquito, can become infected with West Nile virus. When the mosquito feeds on a human, the virus can be transmitted. Photo by Jim Gathany, CDC, courtesy of Wikimedia Commons.