genetic forms. These profiles are sometimes quite specific and dependent on the original geographic location of the virus. Several recent studies have characterized the RNA profiles of WN viruses including several isolates from the NYC outbreak. The results show that all the NYC WN virus isolates were almost identical to one another. All the NYC WN isolates share very close affinity with a 1998 WN virus isolated from a goose in Israel. This finding that there is only a single genetic strain of WN in North America would certainly fit the possibility that the virus was recently introduced and it had not resided in North America long enough to diverge into additional strains. THE FUTURE OF WEST NILE VIRUS IN NORTH AMERICA. Regardless of its source, WN virus is likely here to stay in North America. If and when it spreads from the NYC metropolitan area remains to be seen. Of importance, has been the question of whether this virus will persist through the winter, either in a vertebrate reservoir, or perhaps in an overwintering mosquito. Current observations indicate that both liklihoods for persistence have indeed occurred. Three pools of Culex species collected during January and February 2000 at Fort Totten, New York City (northeastern Queens) yielded WN virus RNA using a very sensitive assay called reverse transcriptase polymerase chain reaction (RT-PCR). On subsequent analysis using a Vero cell culture, one of the three RT-PCR positive pools was found to contain live WN virus. This was then confirmed using a WN-specific monoclonal antibody staining of infected cells and by virus gene sequencing.In mid-February 2000 WN virus was isolated from a Red-tailed Hawk found moribund near Bronxville, New York (north of NYC and east of Yonkers, NY). These data indicate that, as of mid-winter 2000, live WN virus was still extant in the NYC metropolitan area.Factors that may facilitate dispersal of WN include the movement of infected humans, infected ...
