Virus isolations from mosquitoes in southern Ontario, 1976 and 1977

Following the 1975 epidemic of St. Louis encephalitis (SLE) in Ontario, programs were instituted to monitor virus activity in mosquito populations during 1976 and 1977. Mosquitoes were trapped with CDC light traps and CO2 cone traps, pooled by species, and tested for virus by intracerebral inoculation of suckling mice. In 1976, 51 175 mosquitoes were tested. SLE virus was isolated from two mixed pools of Culex pipiens--C. restuans mosquitoes. Five isolations of California serogroup viruses were made. Three of these were trivittatus virus, which has not been demonstrated previously in Canada, and the other two were snowshoe have virus. Other viruses isolated in 1976 were a virus antigenically identical to the virus of infectious bursal disease of chickens and 34 Flanders viruses. In 1977, 34 428 mosquitoes were tested. Flanders virus was isolated most frequently, from pools of mixed C. pipiens--C. restuans mosquitoes. The only other isolate was a Bunyamwera group virus, Cache Valley virus. This virus has not been reported previously in Ontario.