A variant of La Crosse virus attenuated for Aedes triseriatus mosquitoes.

A plaque-purified variant was cloned from prototype La Crosse (LAC) virus. This variant (PP-31) was lethal to suckling mice by the intracerebral route, produced "wild-type" plaques in Vero and BHK-21 cells, and grew to high titers (greater than 10(7) PFU/ml) in suckling mice and in cell culture. The variant was able to orally infect the vector, Aedes triseriatus; however, it was unable to escape infected midgut cells and disseminate to secondary target organs. Large, atypical, focal accumulations of viral antigen were detected in these midguts by immunofluorescence. Orally infected mosquitoes were unable to transmit virus by bite to suckling mice or vertically to their progeny. Even after inoculation of the variant virus into mosquitoes, there appeared to be a restriction on cell to cell virus movement. The role such variants may play in the modulation of infection in an arthropod vector is discussed.