We evaluated the potential for several North American mosquito species to t
ransmit the newly introduced West Nile (WN) virus. Mosquitoes collected in
the New York City Metropolitan Area during the recent (1999) WN outbreak we
re allowed to feed on chickens infected with WN virus isolated from a crow
that had died during this outbreak. These mosquitoes were tested approximat
ely 2 weeks later to determine infection, dissemination, and transmission r
ates. Culex pipiens mosquitoes were highly susceptible to infection, and ne
arly all individuals with a disseminated infection did transmit WN virus by
bite. In contrast, Aedes vexans were only moderately susceptible to oral i
nfection; however, those individuals inoculated with WN virus did transmit
virus by bite.