Abstract

Background Serious gastrointestinal infection of Rotavirus (RV) is usually prevalent during winter months and often seen in infants and young children. Studies on genotypes of prevalent rotavirus strains are quite important for preventing infection, developing vaccines, and its evaluation. While at least 11 G genotypes have been isolated from humans, G1, G2, G3, G4, and emerging G9 are major genotypes of human RV. Although G6 human rotavirus is quite rare, it is the major type among rotaviruses from cattle. In this study we investigated the characteristics and origin of bovine RV strains from the children of the Nasu district, Tochigi, Japan. Materials and methods We examined the clinical findings in 147 patients who attended to the Department of Pediatrics at International University of Health and Welfare Hospital in Nasu-shiobara City, Tochigi, Japan during the time of April 1, 2008 to March 31, 2010. We analyzed the clinical findings of the 37 patients with a fecal sample positive for RV antigen on VP6, NSP4 gene RT-PCR genotyping. Viral genotypes were determined using rotavirus-positive samples from 27 of these 37 patients. Results In 37 cases in VP6, NSP4 gene-based RT-PCR 24 samples were positive and the genotypes were determined as G1P[8] in 5 samples, G3P[8] in 5 samples, G9P[8] in 3 samples, and G6P[9] in 2 samples. Of particular note, we detected G6P[9] which were extremely rare in human beings but common in cattle. KF17 strain of a patient showed G6 type of bovine strains and P[9] was admitted to reconcile with human strains. Per match ratio in each gene of VP6, VP1, VP2, VP3, and NSP4 showed a high match rate (84.1-86.4%) with DS-1 type. Per match ratio in each gene of VP4, NSP1, NSP3, NSP4 and NSP5 also showed a high match rate (94.2-96.9%) with AU-1 type. Bovine type strain gene segments become reassortant rotaviruses major two genes in these stocks. Discussion In the phylogenetic analysis the gene of a strain KF17 of G6P[9] was located in a human lineage including　other human G6 strains. Similarly, all other genes of the strain except for the NSP3 gene were relatively closely　related to at least one of the human G6 RVs reported in Europe and the U.S. In a study in Miyagi Prefecture G6P[9] (M72S11) per sample was found from a 2-year-old toddler in 2011. Also G6P[9] have been detected from more than 3 cats of Mie Prefecture. These findings suggest that human G6 RVs which had occurred by reassortment between human and bovine RVs are distributed worldwide, despite low prevalence. G6 RV may occur independently in different areas through reassortment among local strains.

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