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West Nile Virus in the United States

17 Aug 2012

Forty three states in the US have reported West Nile virus (WNV) infections in humans, birds, or mosquitoes in 2012. A total of 693 human cases of WNV infection, including 26 deaths, have been reported to the Centers for Disease Control and Prevention (CDC). Of these, 406 (59%) were classified as neuro-invasive disease (such as meningitis or encephalitis).

The 693 cases reported this far in 2012 are the highest number of WNV infections reported to CDC during this time period since WNV was first detected in the United States in 1999. Over 80% of the cases have been reported from 6 states (Texas, Mississippi, Louisiana, Oklahoma, South Dakota, and California), and almost half of all cases have been reported from Texas.

Advice for Travellers

West Nile virus infection is transmitted by Culex mosquitoes which bite mainly from dusk to dawn. Reservoir hosts are usually birds. Most infections are asymptomatic and severe infection is rare. West Nile virus infection is rarely reported in travellers. Risk is greatest in those undertaking outdoor activities. Travellers should take precautions to prevent mosquito bites especially during summer months.