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

An epizootic outbreak of diarrhea occurred in adult cows on a dairy farm in Hokkaido, Japan. One colostrum-fed calf inoculated with pooled feces of the 5 affected cows, developed mild diarrhea, and shed rotavirus-like particles which reacted with antiserum to group B rotavirus in immune electron microscopy. Cell culture immunofluorescence tests, RNA-polyacrylamide gel electrophoresis and RT-PCR confirmed that this virus was bovine group B rotavirus, 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 etiological agent of the outbreak of adult cow diarrhea. The identities of the nucleotide (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 aa) compared to those of the published corresponding genes from 3 bovine and 2 other mammalian (human and rat) strains of group B rotaviruses, respectively. To our knowledge, this is the first report on the presence of bovine group B rotavirus in Japan.