West Nile virus: an emerging virus in North America.

West Nile virus is an emerging virus that first appeared in North America during the summer of 1999 in New York City. There were seven deaths associated with this event. Surveillance reports indicate that the virus had been spreading south and west and in 2002, had been reported in 42 states and the District of Columbia. As of September 2002, there were 2121 total human cases reported, induding 104 deaths. The fatality rate for the West Nile virus is very low and the majority of individuals will have no clinical symptoms; however, individuals at most risk for more serious form of the disease are the elderly, the immunocompromised, and young individuals. The virus is spread by certain mosquito species and certain populations of birds serve as the reservoir hosts. Because person-to-person transmission does not occur, humans are therefore considered dead-end hosts. Confirmation of cases West Nile virus infections in humans are determined based on clinical and laboratory findings.