Transovarial transmission of LaCrosse virus in Aedes triseriatus

As part of a continuing investigation on the ecology of LaCrosse virus in Wisconsin, field and laboratory studies were conducted to explore the possibility that the virus is transmitted transovarially in A. triseriatus mosquitoes. In laboratory experiments, A. triseriatus mosquitoes were infected by ingesting LaCrosse virus in defibrinated blood. LaCrosse virus was recovered from F1 eggs, larvae, and adults that originated from the infected parent mosquitoes. In a subsequent field study aimed at determining if transovarial transmission accounted for the survival of LaCrosse virus during the winter season, larvae that originated from overwintering A. triseriatus eggs were collected from a LaCrosse virus enzootic area in southwestern Wisconsin. LaCrosse virus was isolated from these larvae and from adult A. triseriatus that were reared from field-collected larvae. These findings strongly imply that A. triseriatus is the reservoir of LaCrosse virus and that transovarial transmission is the mechanism responsible for the maintenance of the virus during the winter season in the north central region of the United States.