The economic impact of the deadly West Nile virus has been substantially underestimated, according to a new report from the Centers for Disease Control and Prevention. West Nile virus, which spreads via infected mosquitoes, was first detected in New York in 1999. This report suggests that West Nile may require more attention than previously thought, but its still a relatively minor health care cost. There have been more than 37,000 cases of West Nile virus in the US since 1999