Known mosquito hosts of western encephalitis virus in Saskatchewan.

Abstract

Seven species of Saskatchewan mosquitoes have been found infected with the virus of western encephalitis (WE) in nature. The majority of WE virus isolations from mosquitoes were made during July and August, the months when epidemics begin. In 2 epidemic years the majority of the isolations from mosquitoes were from Culex tarsalis which had higher seasonal infection rates and generally larger infected populations than any other species in 5 collecting areas. In 1 interepidemic year, isolations of WE virus from species of mosquitoes other than C. tarsalis predominated and in at least 1 locality 1 of these species had a high seasonal infection rate and a relatively large infected population. Based on ecological and epidemiological evidence, it is concluded that, in Saskatchewan, C. tarsalis is the principal epidemic transmitter of the WE virus and that other species maintain the enzootic status of the disease. On similar grounds, Culiseta inornata may be a significant transmitter of the virus in epidemics of WE-in horses in Saskatchewan. Infected mosquitoes have been found in most of the agricultural area of the province except the Southwest, but testing of larger numbers of specimens from the Southwest would probably reveal infected mosquitoes in that area.