Molecular basis of bunyavirus per os infection of mosquitoes: role of the middle-sized RNA segment.

The molecular basis of bunyavirus per os infection of mosquitoes was determined; La Crosse (LaC), snowshoe hare (Ssh), and LaC-Ssh reassortment viruses were compared for their ability to infect Aedes triseriatus, the natural vector of the LaC virus. The viruses were comparable in their ability to infect midgut cells; 115 of 117 (98%) mosquitoes ingesting viruses containing the LaC middle-sized RNa segment and 92/100 (92%) of mosquitoes ingesting viruses containing the Ssh middle-sized RNA segment became infected. However, those viruses containing the LaC middle-sized RNA segments disseminated efficiently (113/115, 98%) from the midgut to infect secondary target organs. Those viruses containing the Ssh middle-sized RNA segment efficiently infected the midgut and large amounts of viral antigen were detected in the midgut cells but antigen was detected in the secondary target organs only in 26% (24/92) of the mosquitoes with midgut infection. Thus, the middle-sized RNA segment seems to be the major determinant for successful dissemination of LaC virus from infected A. triseriatus midgut cells.