Those who become ill may develop West Nile encephalitis, an inflammation of the brain.
There is no vaccine or specific treatment for West Nile virus.
According to the CDC, only 1% of people bitten by West Nile-infected mosquitoes become seriously ill.
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2003 – 9,862 cases of West Nile Virus were identified in the United States with 264 fatalities.
2002 – 4,156 cases of West Nile Virus were reported in 39 states and the District of Columbia with 284 fatalities.
1999-2001 – 149 cases of West Nile virus were reported in the United States with 19 fatalities.