Sequence and phylogenetic analyses of nonstructural protein 2 genes of species B porcine rotaviruses detected in Japan during 2001–2009

Porcine rotavirus B (RVB) has been often detected in diarrhea of suckling and weaned pigs. Because it is difficult to serially cultivate RVBs in cell culture, the number of available sequence data for RNA segments other than VP7 and NSP1 in especially porcine RVBs is still limited. We performed genetic analysis focusing on nonstructural protein 2 (NSP2) using several porcine RVB strains, which were detected in diarrheic feces collected around Japan during 2001-2009. Comparison of NSP2 nucleotide and deduced amino acid sequences from porcine RVB strains exhibited low identities (64.0-99.9% in nt and 66.7-100.0% in aa) to those of other RVB strains. Phylogenetic analysis of RVB NSP2 revealed the presence of four clusters (N1-N4) including human plus murine, bovine and porcine clusters with cut-off values of 75% at the nt and 85% at the aa level. Furthermore, the NSP2 genes of porcine RVBs were divided into three genotypes, of which some porcine RVBs belonged into bovine-cluster. PB-70-H5 and PB-70-H3, which belonged to same pig farm, might be identical in NSP2 gene as shown sequence identity of 99.9%, nevertheless both had different VP7 genes each other. Thus, this data demonstrates the occurrence of gene reassortment among porcine RVBs derived from same pig farm. Our findings presented here would provide more valuable information to elucidate evolution of RVBs.