Mosquito surveillance for West Nile Virus in Connecticut, 2000: Isolation from Culex pipiens, Cx. restuans, Cx. salinarius, Culiseta melanura

Fourteen isolations of West Nile (WN) virus were obtained from four mosquit o species (Culex pipiens [5], Cx. restuans [4], Cx. salinarius [2], and Cul iseta melanura [3]) in statewide surveillance conducted from June through O ctober 2000. Most isolates were obtained from mosquitoes collected in dense ly populated residential locales in Fairfield and New Haven counties, where the highest rates of dead crow sightings were reported and where WN virus was detected in 1999. Minimum field infection rates per 1,000 mosquitoes ra nged from 0.5 to 1.8 (county based) and from 1.3 to 76.9 (site specific), C x. restuans appears to be important in initiating WN virus transmission amo ng birds in early summer; Cx. pipiens appears to play a greater role in amp lifying virus later in the season. Cs. melanura could be important in the c irculation of WN virus among birds in sylvan environments; Cx. salinarius i s a suspected vector of WN virus to humans and horses.