NATURAL VERTICAL TRANSMISSION OF WESTERN EQUINE ENCEPHALOMYELITIS VIRUS IN MOSQUITOS

The mechanism by which western equine encephalomyelitis (WEE) virus an d other mosquito-borne alphaviruses (Togaviridae) survive during perio ds of vector inactivity is unknown. Recently, three strains of WEE vir us were isolated from adult Aedes dorsalis collected as larvae from a salt marsh in a coastal region of California. This provides evidence o f vertical transmission of WEE virus in mosquitoes in nature. Vertical transmission in Ae. dorsalis and closely related mosquito species may be an important mechanism for the maintenance of WEE virus in tempera te regions in North America where horizontal transmission of the virus is seasonal.