Role of rotavirus vaccination on G9P[8] rotavirus strain during a seasonal outbreak in Japan.

Although two live oral rotavirus (RV) vaccines, Rotarix and RotaTeq, play a critical role toward reducing disease severity, hospitalization, and death rate in RV infections, regular monitoring of vaccine effectiveness (VE) is yet necessary because the segmented genome structure and reassortment capability of RVs pose considerable threats toward waning VE. In this study, we examined the VE by a test-negative study design against G9P[8]I2 strain during a seasonal outbreak in February-May, 2018, in an outpatient clinic in Kyoto Prefecture, Japan. It remains important because G9P[8]I2 strain remains partially heterotypic to these vaccines and predominating in post-vaccination era. During year-long surveillance, RV infections were detected only from February to May. During this outbreak, 33 (42.3%) children out of 78 with acute gastroenteritis (AGE) remained RV-positive, of which 29 (87.8%) children were infected with G9P[8]I2. Two immunochromatographic (IC) assay kits exhibited 100% sensitivity and specificity to detect G9P[8]I2 strain. Only 23.2% children were found to be vaccinated. Yet, significant VE 69.7% (95% CI: 2.5%-90.6%) was recognized against all RV strains that increased with disease severity. Similar significant VE 71.8% (95% CI: 1%-92%) was determined against G9P[8]I2 strain. The severity score remained substantially low in vaccinated children. Our data reveal that vaccine-preventable G9P[8]I2 strain yet may cause outbreak where vaccination coverage remains low. Thus, this study emphasizes the necessity of global introduction of RV-vaccines in national immunization programs of every country.

Emergence of intragenotype recombinant sapovirus in Japan.

Sapovirus is an important causative agent of sporadic cases as well as of outbreaks of acute gastroenteritis in humans worldwide. A total of 603 fecal specimens collected from July 2005 to June 2006 from children with acute gastroenteritis in five localities in Japan (Maizuru, Tokyo, Sapporo, Saga, and Osaka) were screened for sapovirus by RT-PCR. It was found that 17 specimens were positive for sapovirus and it represented 2.8%. Interestingly, intragenotype recombinant sapovirus GI/1 emerged with 76.4% (13 of 17) and rapidly became the leading cause of acute gastroenteritis in Japan for the first time. The lower frequency of sapovirus GI/2 and GI/4 (each of 11.8%), which were the second prevailing genotypes, was also detected. A novel nomenclature of sapovirus was proposed, in which worldwide sapovirus strains were classified into seven genogroups. Of these, novel sapovirus genogroups VI and VII demonstrated the very low homologies, only 32.8-41.6% at the amino acid level and 43.6-49.9% at the nucleotide level, to those of sapovirus genogroups I-V. Of note, two distinct clusters of sapovirus were co-circulating in porcine. Interestingly, the worldwide sapovirus strains shared the 25 nucleotide-conserved region, covering the polymerase-capsid junction which differed according to each species due to multiple nucleotide substitutions. The finding suggests that the sapovirus recombination between human and animal hardly takes place in nature. This is also the first, to our best knowledge, demonstrating the emergence of the intragenotype recombinant sapovirus with its causing diarrheal illness in Japan.

Novel intragenotype recombination in sapovirus.

Based on the genetic analysis, a novel, naturally occurring recombination between two distinct sapovirus subtypes (subtype a and subtype b) within genogroup I genotype 1 was identified. Breakpoint analysis of recombinant sapovirus showed that the recombination site was at the polymerase-capsid junction. This is the first report of the existence of acute gastroenteritis caused by intragenotype recombinant sapovirus. The results also provided evidence that the natural recombination occurs not only in sapovirus genogroup II but also in sapovirus genogroup I.

Detection and genetic characterization of group A rotavirus strains circulating among children with acute gastroenteritis in Japan.

A total of 603 fecal specimens collected from July 2005 to June 2006 from children with acute gastroenteritis, encompassing five different localities in Japan, were screened for group A rotavirus by reverse transcription-PCR. It was found that 117 fecal specimens (19.4%) were positive for group A rotavirus. Rotavirus infection was detected continuously from November to June, with the highest prevalence in April. The G (VP7 genotypes) and P (VP4 genotypes) types were further investigated. The predominant genotype was G1P[8] (70.1%), followed by G3P[8] (17.9%), G9P[8] (6.8%), and G2P[4] (2.6%). A number of unusual G1P[4] combinations were also detected during this study period. A novel nomenclature for G1 is proposed, in which worldwide rotavirus G1 strains are classified into 11 lineages with 17 sublineages. A wide range of amino acid substitutions (up to 34) in VP7 that are specific for G1 lineages and sublineages were identified. Interestingly, only short amino acid motifs located at positions 29 to 75 and 211 to 213 of VP7 defined correctly the phylogenetic G1 lineages and sublineages. Examination of the deduced sequences of antigenic regions of VP7 also revealed multiple particular amino acid substitutions that correlated with the phylogenetic G1 lineages and sublineages. Of note, at least three distinct clusters of rotavirus G1 isolates were cocirculating in the Japanese pediatric population studied.