Detection and characterization of a human G9P[4] rotavirus strain in Japan.

In a surveillance system in Osaka City, Japan, 48 sporadic rotavirus A (RVA) infections were detected during 2008/2009-2011/2012 seasons. The G/P-genotypes of detected RVAs were G1P[8], G2P[4], G3P[8], G9P[4], and G9P[8]. Although G9P[4] is a rare genotype that had not been reported in Japan, it was the second most prevalent genotype, following G1P[8], and accounted for 35.3% of RVA cases in the 2011/2012 season. Further genotyping revealed that the G9P[4] strain had genotype 2 internal protein genes except for NSP3: G9-P[4]-I2-R2-C2-M2-A2-N2-T1-E2-H2. Among detected RVA strains, G9P[4] and some G9P[8] strains shared high nucleotide identity in VP7 and NSP3 genes. Phylogenetic and BLAST search analyses showed that the G9P[4] strain in Japan shared high nucleotide identity in genotype 2 genes with common G2P[4] strains circulating globally, but was distinct from other G9P[4] strains circulating worldwide. These results suggest that the G9P[4] strain in Japan may have emerged through an independent reassortment between G9P[8] and G2P[4]. Finally, the role of NSP3 protein in the circulating RVA from an amino acid comparison between T1- and T2-type NSP3 is discussed. These findings provide an important insight into less problematic combinations of circulating RVA genes derived from different genotypes.