West Nile virus (WNV)
West Nile virus (WNV) is the most commonly transmitted virus to humans by mosquitoes in the U.S. Fortunately, most people infected with WNV will have no symptoms. According to Centers for Diseases Control and Prevention (CDC), about 1 in 5 people who are infected will develop a fever with other symptoms and less than 1% of infected people will develop a serious, sometimes fatal, neurologic illness.
West Nile virus first appeared in the United States in 1999 (Figure 1) and subsequently spread throughout the U.S. and into Canada, Mexico, and several Central and South American countries. Cases have been reported from every state except Alaska. It took only a four years for the virus to spread across the entire country causing major epidemics along the way (Figure 2).