Formation of reassortant bunyaviruses in dually infected mosquitoes

Wild-type and temperature-sensitive ( ts) bunyaviruses were recovered from Aedes triseriatus mosquitoes after 1–3 weeks extrinsic incubation following intrathoracic inoculation with homologous virus mixtures of Group I and II ts mutants of showshoe hare (SSH), or La Crosse (LAC) viruses (e.g., SSH I and SSH II mutants, or LAC I and LAC II mutants). Wild-type and ts viruses were also recovered from mosquitoes dually infected with heterologous virus mixtures of SSH I and LAC II ts mutants. However, only ts viruses have been obtained from mosquitoes infected with LAC I and SSH II ts mutants. RNA fingerprint analyses of one of the wild-type viruses recovered from a mosquito infected with the SSH I and LAC II ts mutants showed that it had the reassortant virus large/medium/small RNA genotype of SSH/LAC/SSH. Wild-type and ts viruses were also recovered from suckling mice on which mosquitoes that had been infected with homologous virus Group I and II SSH, or LAC, ts mutants were allowed to feed. Likewise wild-type and ts viruses were recovered from mice on which mosquitoes inoculated with SSH I and LAC II ts mutants were allowed to feed. RNA fingerprint analyses of one of these wild-type viruses indicated that it had the reassortant virus genotype of SSH/LAC/LAC. From mice on which mosquitoes infected with SSH II and LAC I ts mutants had fed, no wild-type viruses were recovered. The inability to detect reassortants having LAC/SSH/LAC and LAC/SSH/SSH genotypes from the in vivo infections expected to yield them (i.e., SSH II plus LAC I) was consistent with previous observations in which such reassortants were only recovered at very low frequencies from in vitro recombination analyses ( E. J. Rozhon, P. Gensemer, R. E. Shope, and D. H. L. Bishop, Virology, 1981, in press).