Sequence analysis of the VP7 and VP4 genes identifies a novel VP7 gene allele of porcine rotaviruses, sharing a common evolutionary origin with human G2 rotaviruses

During an epidemiological survey encompassing several porcine herds in Saragoza, Spain, the VP7 and VP4 of a rotavirus-positive sample, 34461-4, could not be predicted by using multiple sets of G- and P-type-specific primers. Sequence analysis of the VP7 gene revealed a low amino acid (aa) identity with those of well-established G serotypes, ranging between 58.33% and 88.88%, with the highest identity being to human G2 rotaviruses. Analysis of the VP4 gene revealed a P[23] VP4 specificity, as its VP8* aa sequence was 95.9% identical to that of the P14[23],G5 porcine strain A34, while analysis of the VP6 indicated a genogroup I, that is predictive of subgroup I specificity. Analysis of the 10th and 11th RNA segments revealed close identity to strains of porcine and human origin, respectively. The relatively low overall aa sequence conservation (<89% aa) to G2 human rotaviruses, the lack of N-glycosylation sites that are usually highly conserved in G2 rotaviruses, and the presence of several amino acid substitutions in the major antigenic hypervariable regions hampered an unambiguous classification of the porcine strain 34461-4 as G2 serotype on the basis of sequence analysis alone. The identification of a borderline, G2-like, VP7 gene allele in pigs, while reinforcing the hypotheses of a tight relationship in the evolution of human and animal rotaviruses, provides additional evidence for the wide genetic/antigenic diversity of group A rotaviruses.