Characterization of human rotavirus serotype G9 isolated in Japan and Thailand from 1995 to 1997

Serotyping of human rotavirus was conducted in 396 Japanese and 100 Thai ro tavirus-positive fecal specimens collected from 1995 to 1997. Serotype G9 w as found to be the third most common serotype with frequency of 16.2% in Th ailand from 1996 to 1997. It was also detected in Japan with a low frequenc y (0.7%) in this year. The genetic analyses of VP4 and NSP4 genes of these G9 strains showed that 1 strain from Japan possessed P[8] genotype and NSP4 Wa-group with long electropherotpe (e-type). In contrast, 5 strains from T hailand belonged to P[6] and 1 strain belonged to P[4]. All of the Thai str ains were in the NSP4 KUN-group with a short e-type. Sequence analysis of t heir VP7 gene revealed that there was the highest homology among fecal G9 s trains (> 96.3%, amino acid identity) and a relatively high degree of homol ogy to standard viruses, F45 from Japan (95.4-96.3%, amino acid identity) a nd 116E from India (92-92.3%, amino acid identity). However, immunological analysis using G9 specific monoclonal antibodies (Mabs) against VP7 protein showed that the G9 strains isolated from the two countries had different a ntigenic specificity. It was confirmed further by intraserotypical phylogen etic analysis of VP7 amino acid. These results indicated that the prevalenc e of G9 rotavirus in 1996-1997 in Thailand was relative to the continuing r ecent emergence of it on a worldwide basis, while the Japanese G9 strain is olated in this survey was identified to have progenitors common to the F45 strain that was prevalent in 1985 in Japan. Phylogenetic analysis of VP7 am ino acid of G114 prototype rotavirus showed that the G9 strains were most c losely related to the equine G14 rotavirus F123 strain but G3 strains, inte rserotypically. These findings suggest that G9 rota-viruses might be divide d into two or more subtypes. (C) 2001 Wiley-Liss, Inc.