Genomic and biologic analyses of snowshoe hare virus field and laboratory strains.

Low-passage field strains of snowshoe hare (SSH) virus (Bunyaviridae), the prototype SSH virus (originally isolated in Montana), and La Crosse (LAC) virus were compared serologically by plaque-reduction neutralization (PRNT) and molecularly by oligonucleotide fingerprinting (ONF). The PRNT and ONF results confirmed the identity of the field strains, although some differences in the fingerprints were observed. We have examined the RNA genome variability in the two field and three laboratory strains of SSH virus, using direct sequence analysis of selected RNase T1 oligonucleotides. Few changes were observed among three Montana prototype-derived laboratory isolates, although they have different passage histories. In contrast, the field isolates differed greatly from the laboratory strains. In addition, we have located several of the larger T1 oligonucleotides within the known sequence of the small and large RNA genome segments. We then compared the viruses for their ability to replicate in and be transmitted by Aedes triseriatus mosquitoes. The oral infection rates for LAC, the field isolates, and the SSH prototype, as determined by immunofluorescent examination of midgut tissues, were 100%, 82%, and 47%, respectively. All viruses were also transmissible from mosquitoes to mice.