Isolations of Jamestown canyon virus (Bunyaviridae: California serogroup) from mosquitoes (Diptera: Culicidae) in the western United States, 1990-1992.

Nearly 80,000 immature and adult mosquitoes in three genera were collected in high-elevation (> 1,000 m) areas of California (68,229), Nevada (3,721), Oregon (5,918), and Washington (1,629) during 1990-1992 and tested for virus as adult males or females in 1,799 pools. Collections comprised primarily alpine Aedes in the Aedes communis (De Geer) group of the subgenus Ochlerotatus. Thirteen strains of Jamestown Canyon (JC) virus were recovered by plaque assay in Vero cell culture from three members of the Ae. communis group: 10 from Aedes tahoensis Dyar, 2 from Aedes cataphylla Dyar, and 1 from Aedes hexodontus Dyar. All isolates came from collections made in Alpine, Sierra, Tulare, or Tuolumne counties in the Sierra Nevada of California. Vertical transmission of JC virus in all three mosquito species was demonstrated by the isolation of virus from adult males or females reared from field-collected larvae or pupae. The prevalence of infected Ae. tahoensis was significantly higher in field-collected adult females than in reared adult males and females in Alpine County, which indicated that JC virus was being amplified by horizontal transmission. This study further incriminated Ae. tahoensis, Ae. cataphylla, and Ae. hexodontus as natural vectors of JC virus in California and greatly extended the known geographical range of this virus in the Sierra Nevada.