First detection of bovine group B rotavirus in Japan and sequence of its VP7 gene

An epizootic outbreak of diarrhea occulted in adult cows on a dairy farm in Hokkaido, Japan. One colostrum-fed calf inoculated with pooled feces of th e 5 affected cows, developed mild diarrhea, and shed rotavirus-like particl es which reacted with antiserum to group B rotavirus in immune electron mic roscopy. Cell culture immunofluorescence tests, RNA-polyacrylamide gel elec trophoresis and RT-PCR confirmed that this virus was bovine group B rotavir us, which was designated the Nemuro strain. Additional 2 colostrum-deprived calves inoculated with feces of the first calf also developed diarrhea and shed virus, suggesting that this group B rotavirus might be the etiologica l agent of the outbreak of adult cow diarrhea. The identities of the nucleo tide (nt) and deduced amino acid (aa) sequences of the Nemuro VP7 gene were high (93-95% in nt and 96-97% in aa) and low (61-63% in nt and 49-61% in a a) compared to those of the published corresponding genes from 3 bovine and 2 other mammalian (human and rat) strains of group B rotaviruses, respecti vely. To our knowledge, this is the first report on the presence of bovine group B rotavirus in Japan.