ns of illness was captured in Egypt. Domestic pigeons are abundant in urban settings and may prove to be particularly important in epidemics such as that observed in NYC during the summer of 1999.WN viruses have been isolated from the peripheral blood of infected humans, especially during the first few days of clinical illness. Studies were done in Israel where consecutive daily blood samples were collected and analyzed for virus. West Nile virus isolation rates were 77% for the first day of infection, 27% for day 2, 18% for day 3, and 6% for day 4. Twenty-three strains of WN virus were isolated from febrile children in Egypt during the early 1950s.WEST NILE VIRUS IN NEW YORK CITY The mechanism(s) by which WN was introduced into NYC is likely to be a topic of spirited debate. Several introduction mechanisms are possible. First, it is possible that WN has been maintained in low-level transmission cycles in the northeastern USA for many years and only became evident during the summer and early autumn of 1999. This surge of epidemic activity may have been due to environmental conditions that pre-disposed the NYC area to the epidemic transmission of a flavivirus like WN. Urban epidemics of SLE in North America have typically occurred during extremely dry summers, conditions such as those that existed in NYC during the summer of 1999. Recent introduction of WN to the NYC area is also possible. A newly infected human may have traveled from Africa, Eastern Europe or some other location with a active WN transmission, arriving in NYC just as their viremia (the amount of virus in their peripheral blood) peaked. If an individual's viremia is high enough to infect vector mosquitoes ( Cx. pipiens in NYC), some of the mosquitoes that feed on the infected blood will become infective. Newly infected mosquitoes require a temperature-dependent extrinsic incubation period (EIP), usually lasting at least 2 weeks, before they become infective. Virus replica...
