Prevalence and molecular characterization of G1P[8] human rotaviruses possessing DS-1-like VP6, NSP4, and NSP5/6 in Japan.

During a survey of human rotaviruses in Okayama Prefecture, Japan in the 2011-2012 rotavirus season (between September 2011 and August 2012), G3P[8] was found to be a predominant genotype overall. However, G1P[8] emerged in the latter half of the season. To clarify the genetic background of the G1P[8] strains, the VP7, VP4, VP6, NSP4, and NSP5/6 genes of the strains were sequenced and genotyped. As a result, it was demonstrated that the strains with two different genotype constellations (G1-P[8]-I1-E1-H1 and G1-P[8]-I2-E2-H2) prevailed in the season. The G1P[8] strains possessing the DS-1-like VP6, NSP4, and NSP5/6 genes (the DS-1-like G1P[8] strains), which should reveal a short electropherotype, were originated from possible intergenogroup reassortment events. The DS-1-like G1P[8] strains accounted for 74.1% of all G1P[8] strains and were detected continuously throughout the season but not in the preceding season, indicating the possibility of new introduction and rapid spreading of these strains in the 2011-2012 season. The results suggest that the intergenogroup reassortants, considered generally unstable, can spread rapidly and become relevant.

Molecular characterization of OP354-like P[8] (P[8]b subtype) human rotaviruses A species isolated in Japan.

OP354-like P[8] (P[8]b subtype) species A rotaviruses (RVAs) were isolated first time in Japan during a RVA survey in Okayama Prefecture between 2006 and 2009. Two of 236 RVA-positive samples were identified as G1P[8]b by reverse transcription polymerase chain reaction. P[8]b strains (RVA/human-wt/JPN/OH1998/2008/G1P[8]b and RVA/human-wt/JPN/OH2024/2008/G1P[8]b) were isolated only in May, 2008 and both patients infected with P[8]b viruses lived in the same city, suggesting that the prevalence of P[8]b RVAs is limited considerably in Okayama Prefecture. Molecular analysis of four genes (VP4, VP6, VP7, and NSP4 genes) of Japanese P[8]b strains revealed that the VP4 genes of these strains were related closely to those of Southeast Asian and Indian P[8]b strains. In contrast, the VP6, VP7, and NSP4 genes of Japanese P[8]b strains were highly homologous to G1P[8]a strains prevalent in the same area. These results suggest that the Japanese P[8]b strain may be a result of reassortment events between Japanese G1P[8]a viruses and unidentified Asian viruses possessing the P[8]b VP4 gene.

Rotavirus antigenemia and genomia in children with rotavirus gastroenteritis.

We investigated group A rotavirus (GARV) antigenemia and genomia in children with rotavirus gastroenteritis. A total of 16 patients (2-29 months old), who received a diagnosis of GARV gastroenteritis using a commercial rapid test, were enrolled in this study. The sera from the patients were tested for the presence of GARV antigen and the VP7 and NSP3 genes using an enzyme-linked immunosorbent assay (ELISA) and reverse transcription-polymerase chain reaction, respectively. Furthermore, when the VP7 gene was amplified, G type was identified and compared with that of GARV from the fecal samples of the patients. GARV antigen was detected in 12 of 16 serum samples (75.0%). No GARV antigen was found in infants that were 6 months old or younger. Thirteen of 16 serum samples (81.3%) were positive for GARV genes. In cases where both antigen and gene analyses were conducted, either GARV antigens or genes, or both, were detected in all cases. The GARV antigen levels of serum collected at 2 days of illness or more were significantly higher than were the levels in the samples obtained from the 1st day. Furthermore, the ELISA optical density values of patients with convulsion were significantly higher than were those of patients without convulsion, suggesting that the antigen level is associated with disease severity.

Detection and molecular characterization of human group C rotaviruses in Okayama Prefecture, Japan, between 1986 and 2005.

A survey of human group C rotaviruses (CHRVs) was conducted in Okayama Prefecture, Japan, over a period of 19 years between 1986 and 2005. The presence of CHRVs was screened by enzyme-linked immunosorbent assay using CHRV-specific monoclonal antibodies and confirmed by reverse transcription-PCR. Of the 3,722 fecal specimens from sporadic cases of gastroenteritis, 44 specimens (1.2%) were positive for CHRV. The CHRV isolates were detected periodically but continuously, and the rates of positivity changed from one rotavirus season to the next. Moreover, the isolates were mainly detected in April and May, and the mean age of the patients infected with CHRV was 5.27 years. The genome electropherotypes (E types) of the isolates were classified into three patterns, and the dominant pattern changed from year to year. Nucleotide sequences of the VP7 and VP4 genes of 16 strains, which were representatives of 70 isolates from sporadic cases and outbreaks, were determined and analyzed. Although the VP7 and VP4 genes of the strains were closely related to each other, a phylogenetic analysis suggested that each of the VP7 and VP4 genes of the strains were grouped into three genetic lineages. Moreover, the strains could be divided into five types based on the combination of the E type and the genetic lineages of the VP7 and VP4 genes. These results indicate that CHRVs generally exist in Okayama Prefecture and that CHRVs with various genomic backgrounds prevailed in a limited area.

Epidemiology of acute gastroenteritis outbreaks caused by Noroviruses in Okayama, Japan.

Noroviruses (called formerly "Norwalk-like viruses") cause food-borne gastroenteritis outbreaks. These outbreaks were thought to be related to shellfish consumption, although non-shellfish related outbreaks also occurred frequently in Japan. To clarify the epidemiology of Norovirus outbreaks, 435 stool samples were collected from 60 acute non-bacterial gastroenteritis outbreaks occurring over 8 years in Okayama, Japan. Using reverse transcription-PCR (RT-PCR), Noroviruses were detected in 257 cases (59.1% of all samples) from 46 outbreaks (77% of all outbreaks). The majority of the 46 Norovirus outbreaks (89%) occurred during November to March; notably one-third occurred in December. Restaurants, schools, and welfare institutions accounted for the major settings in 50%, 20%, and 15% of the Norovirus outbreaks, respectively. This was similar to other reports from Japan, but differed from those from the United Kingdom. The transmission routes were assigned in 27 of the Norovirus outbreaks. In 18 outbreaks the routes were related to human contact (7 from food handlers and 11 from person-to-person contact), whereas those related directly to shellfish occurred only in 9 outbreaks. These results suggest that transmission routes related to human contact are more important than recognized previously in the context of preventive medicine. Furthermore, all outbreaks in which some of the samples contained dual genogroups of Noroviruses were related to shellfish, suggesting that consumption of contaminated shellfish frequently results in mixed Norovirus infections in contrast to other transmission routes and that coexistence of genogroups is a useful marker for shellfish-related outbreaks.

[Outbreak of acute gastroenteritis caused by human group C rotavirus in a youth educational center in Okayama Prefecture].

In May 2000, an outbreak of acute gastroenteritis caused by human group C rotavirus (CHRV) occurred in a youth educational center located in the southern area of Okayama Prefecture. A total of 172 schoolchildren and teachers, who consisted of 51 persons belonging to F school and 121 persons belonging to K school, joined in an educational program at the center from May 24 to 26. Eighty-seven individuals (50.6%) of them showed clinical symptoms of gastroenteritis from May 24 to 30, and the outbreak peaked on May 27. The major clinical symptoms were abdominal pain (87.4%), diarrhea (50.6%), nausea or vomiting (21.8%), fever > 37 degrees C (12.6%), and headache (14.9%). The clinical symptoms of the patients in F school were more severe than those in K school. Thirty-two fecal specimens were collected from the patients and examined for gastroenteritis viruses by electron microscopy, ELISA, reverse passive hemagglutination test, and reverse transcription (RT)-PCR. As a result, CHRVs were detected in 21 specimens (65.6%) by RT-PCR. The possible route of the CHRV infection was thought to be a person to person transmission by following reasons: (i), CHRVs were detected in stools from patients who became ill on the first day of the program; (ii), CHRVs were not detected in stools from cooks; (iii), no possible causal food was found by epidemiological analysis of the outbreak. Furthermore, phylogenetic analysis of the VP7 gene among CHRVs isolated in Okayama revealed that the virus detected in this study was more closely related to the virus isolated from a sporadic case of gastroenteritis in 1996 than that isolated from an outbreak occurred in 1999.