Predominance of porcine rotavirus G9 in Japanese piglets with diarrhea: close relationship of their VP7 genes with those of recent human G9 strains

Abstract

Type G9 of group A rotavirus (GAR) was shown to be predominant in a survey of VP7 (G) and VP4 (P) genotypes among porcine GARs associated with outbreaks of diarrhea in young pigs in Japan between 2000 and 2002. Comparison of the G9 VP7 gene sequences showed that the porcine G9 strains were more closely related to human G9 strains reemerging globally since the mid-1990s than to those from the mid-1980s. The VP7 gene sequences of porcine G9 strains from different farms were divergent (6.1 to 7.2% difference in nucleotides), suggesting that these G9 VP7 genes were not the result of recent introduction into the porcine population. Regarding the P genotype specificities of porcine G9 strains, while the majority of strains were close to unusual porcine P types (P[13] and P[23]), two strains were of the P[6] type, which has closer sequence identity with the human AU19 strain than with the porcine Gottfried strain. These unexpected results suggest that G9 GARs in the porcine population have spread more widely than previously thought and that the VP7 genes of porcine G9 strains and those of some human G9 strains detected recently may have a common progenitor.

FIG. 1.

Electrophoretic migration patterns of viral RNAs from the cultured porcine G9 strains Hokkaido-14, JP3-6, JP13-3, JP16-3, and JP29-6. OSU is a reference porcine G5 strain with a long RNA pattern.

FIG. 2.

Phylogenetic tree for the VP7 genes of human and porcine G9 GAR strains constructed by the Clustal W method and drawn using the TreeView program (22). All of the G9 strains were rooted to strain OSU (G5). Bootstrap values of greater than 700 in 1,000 pseudoreplicates are shown as percentages. The porcine G9 strains presented in this study are boxed. The VP7 nucleotide sequences of human G9 strains used were taken from the following accession numbers or reference: for WI61, reference ; for AU32, AB045372; for F45, reference ; for 116E, L14072; for OM46, AJ491181; for K1, AB045374; for 99-SP1904VP7, AB091754; for 99-TK2091VP7, AB091756; for t203, AY003871; for Mc323, D38053; for Mc345, D38055; for BD524, AJ250543; for MW69, AJ250545; for PH301, AJ491184; for US1205, AF060487; for 95H115, AB045373; for R160, AF274971; for OM526, AJ491182; for R136, AF438228; for SE121, AJ491192; for MR4730-00, AY262749; for GH3574, AY211068; for ISO-3, AF501580; for 00-SP2737VP7, AB091752; and for SD768, AJ491191. Countries and years in which human strains were detected are shown in parentheses.

FIG. 3.

Comparison of the deduced amino acid sequences in five antigenic regions (D, aa 65 to 76; A, aa 87 to 101; B, aa 142 to 152; C, aa 208 to 221; and F, aa 235 to 242) of the VP7 of human and porcine G9 GAR strains. Sequences of porcine G9 strains presented in this study are boxed. For accession numbers of the nucleotide sequences used, refer to the legend of Fig. 2.

FIG. 4.

Phylogenetic tree for the VP8* fragment of VP4 genes from P[6] strains constructed by the Clustal W method and drawn using the TreeView program (22). All the P[6] strains were rooted to strain OSU (P[7]). Bootstrap values of greater than 700 in 1,000 pseudoreplicates are shown as percentages. The porcine G9P[6] strains presented in this study are boxed. The VP4 nucleotide sequences of P[6] strains used were taken from the following accession numbers: M33516 (Gottfried), AB017917 (AU19), L20877 (M37), L33895 (ST3), and AF079356 (US1205).