West Nile Virus infection in mosquitoes, birds, horses, and humans, StatenIsland, New York, 2000

West Nile (WN) virus transmission in the United States during 2000 was most intense on Staten Island, New York, where 10 neurologic illnesses among hu mans and 2 among horses occurred. WN virus was isolated from Aedes vexans, Culex pipiens, Cx. salinarius, Ochlerotatus triseriatus, and Psorophora fer ox, and WN viral RNA was detected in Anopheles punctipennis. An elevated we ekly minimum infection rate (MIR) for Cx. pipiens and increased dead bird d ensity were present for 2 weeks before the first human illness occurred. In creasing mosquito MIRs and dead bird densities in an area may be indicators of an increasing risk for human infections. A transmission model is propos ed involving Cx pipiens and Cx. restuans as the primary enzootic and epizoo tic vectors among birds, Cx salinarius as the primary bridge vector for hum ans, and Aedes/Ochlerotatus spp. as bridge vectors for equine infection.