Multiple isolations of eastern equine encephalitis and highlands J viruses from mosquitoes (Diptera: Culicidae) during a 1996 epizootic in southeastern Connecticut.

Thirty-six isolations of eastern equine encephalitis virus were obtained from 8 species of mosquitoes collected from 5 September through 18 October 1996 during an epizootic in southeastern Connecticut. These included Culiseta melanura (Coquillett) (19 isolates), Culex pipiens L. (8), Culiseta morsitans (Theobald) (3), Aedes sollicitans (Walker) (2), Aedes cantator (Coquillett) (1), Aedes trivittatus (Coquillett) (1), Aedes vexans (Meigen) (1), and Coquillettidia perturbans (Walker) (1). Isolations from Ae. cantator and Ae. trivittaus are new to North American records, and those from Ae. cantator and Ae. sollicitans represent the first infections of human-biting, salt-marsh mosquitoes with eastern equine encephalitis virus in Connecticut. With one exception, eastern equine encephalitis-infected Cs. melanura were found at all sites where eastern equine encephalitis virus was isolated. The large number of eastern equine encephalitis isolations from Cs. melanura and the collection of infected mosquitoes in residential woodlots and coastal salt marshes away from traditional red maple or white cedar swamp habitats, reaffirm the importance of local populations of this mosquito for viral amplification and dispersal from swamp foci. Highlands J virus was more widespread geographically, but fewer isolations of this virus were made from fewer species of mosquitoes. These included Cs. melanura (8 isolates), Cx. pipiens (5), Ae. vexans (3), Aedes canadensis (Theobald) (1), Ae. cantator (1) and Cs. morsitans (1). No human or horse cases of eastern equine encephalitis were reported, although this represents the largest number of isolations for eastern equine encephalitis ever recovered from field-collected mosquitoes in Connecticut.