Phylogenetic analysis of nonstructural protein 5 (NSP5) gene sequences in porcine rotavirus B strains.

Porcine rotavirus B (RVB) has frequently been detected in the diarrhea of suckling and weaned pigs. Because it is difficult to propagate RVBs serially in cell culture, little genetic information about RNA segments other than VP7, NSP1 and NSP2 is available for porcine RVBs. We conducted a phylogenetic analysis focusing on nonstructural protein 5 (NSP5) using 22 porcine RVB strains, which were identified in fecal samples collected around Japan. Sequence analysis showed that NSP5 genes of RVBs contain one ORF, in contrast to the corresponding gene of RVAs that have two ORFs. Comparison of NSP5 amino acid sequences from porcine RVBs with other RVBs revealed that eight serine and serine/threonine residues at the N- and C-terminal regions are highly conserved among RVBs. Phylogenetic analysis also indicated the presence of six clusters (H1-H6) including rat, human, porcine and bovine plus ovine clusters with cut-off values of 78% at the nucleotide level. Moreover, the NSP5 genes of porcine RVBs were divided to three clusters. The data presented here demonstrates that several porcine RVBs with distinctive genotypes are circulating among farms throughout Japan. Our findings provide important new insights into the evolutionary dynamics of RVBs.