Nobuhiro Iritani

Enterovirus 68 in Children with Acute Respiratory Tract Infections, Osaka, Japan

Enterovirus 68 strains were detected in 14 specimens from children with respiratory tract infections and 1 specimen from a child with febrile convulsions during 2010 in Osaka, Japan. These strains had deletions in the 5′ untranslated region and were genetically different from reported strains. This virus is associated with respiratory tract infections in Japan.

Prevalence of Norwalk-Like Virus Infections in Cases of Viral Gastroenteritis among Children in Osaka City, Japan

ABSTRACT Surveillance of Norwalk-like virus (NLV) infections in cases of pediatric gastroenteritis between April 1996 and March 2000 showed that NLVs were an important causative agent in viral gastroenteritis cases among children between November and January in those years. The predominant type of NLV was closely related to Lordsdale virus in genogroup 2. During the 1999-2000 season, Arg320-like strains, which may be genetic recombinants, suddenly appeared and spread.

Human sapovirus classification based on complete capsid nucleotide sequences

The genetically diverse sapoviruses (SaVs) are a significant cause of acute human gastroenteritis. Human SaV surveillance is becoming more critical, and a better understanding of the diversity and distribution of the viral genotypes is needed. In this study, we analyzed 106 complete human SaV capsid nucleotide sequences to provide a better understanding of their diversity. Based on those results, we propose a novel standardized classification scheme that meets the requirements of the International Calicivirus Scientific Committee. We believe the classification scheme and strains described here will be of value for the molecular characterization and classification of newly detected SaV genotypes and for comparing data worldwide.

Increase of GII.2 norovirus infections during the 2009–2010 season in Osaka City, Japan

During the 2009–2010 season, a significant numerical increase of genotype GII.2 norovirus (NoV)‐associated outbreaks was observed in Osaka City, Japan. The most common genotype in that season was GII.2 (44.6%), followed by GII.4 (39.2%). Mostly, GII.2 strains were associated with outbreaks in children and with person‐to‐person contact. The National Infectious Disease Surveillance Center reported that GII.2 NoV infections were widespread in Japan in that season. Comparative phylogenetic analysis of RNA‐dependent RNA polymerase (RdRp) and capsid sequences revealed that this GII.2 epidemic resulted from two genetic strains. The first, GII.2p2 strains, had an identical genotype in the RdRp and capsid genes. GII.2p2 strains in the 2009–2010 season were a different genetic cluster from the strains of spring 2004, the previous epidemic of GII.2 NoV, but showed no unique amino acid change. The second, GII.2 chimera virus (GII.2p16), had GII.16 RdRp and GII.2 capsid genotypes, suggesting prior recombination at the junction of ORF1 and ORF2. GII.2p16 strains had four significant amino acid changes in the P2 subdomain, suggesting antigenic changes. Before the 2009–2010 season, GII.2 chimera viruses had been observed only sporadically. This spreading of GII.2p16 strains in the 2009–2010 season might be the first epidemic of GII.2 chimera virus. This study revealed that the NoV epidemic in the 2009–2010 season differed considerably from the prior season, when GII.4 was predominant. Furthermore, GII.2 strains persisted in human populations by drastic recombination and gradual accumulation of mutations, indicating a prevalent pattern of non‐GII.4 genotypes with genetic evolution. J. Med. Virol. 84:517–525, 2012.

Molecular epidemiology of noroviruses detected in seasonal outbreaks of acute nonbacterial gastroenteritis in Osaka City, Japan, from 1996-1997 to 2008-2009.

In seasons from 1996–1997 through 2008–2009, noroviruses (NoVs) were detected in 505 outbreaks (71%) of nonbacterial gastroenteritis in Osaka City, Japan using molecular diagnosis with reverse transcription (RT)‐PCR or real‐time RT‐PCR. The occurrences of NoV‐associated outbreaks were related with the cold season during November–March (85.3%), and occasionally small epidemics of NoVs occurring during April–June were observed. Oyster‐associated outbreaks were dominant transmission modes (25–61.1%) before the 2003–2004 season, and decreased (5–20.5%) from the 2003–2004 season, although outbreaks attributable to food‐borne transmission (except for oysters) and person‐to‐person contact increased from the 2003–2004 season. The NoV strains were characterized into genotypes based on sequence analysis of partial capsid regions. Genotyping analyses identified at least 30 genotypes (12 in genogroup I [GI] and 18 in genogroup II [GII]) of NoV. The most common genotype was GII.4 (44.6%), followed in order by GII.3, GII.6, GII.2, and GII.5. The number of GII.4 NoVs increased greatly from the 2003–2004 season, eventually comprising a large share among the NoV‐ associated outbreaks (97.4%) of the 2006–2007 season. Occasional increased prevalence of genotypes other than GII.4 was observed during this study period. This study showed the appearance, spread, and disappearance of various genotypes and the change of NoV epidemic in a limited geographic region. Continuous NoV molecular surveillance is important for understanding NoV infections and for improving measures for their control and prevention. J. Med. Virol. 82:2097–2105, 2010.

Detection and genetic characterization of human enteric viruses in oyster‐associated gastroenteritis outbreaks between 2001 and 2012 in Osaka City, Japan

Enteric viruses are an important cause of viral food‐borne disease. Shellfish, especially oysters, are well recognized as a source of food‐borne diseases, and oyster‐associated gastroenteritis outbreaks have on occasion become international occurrences. In this study, 286 fecal specimens from 88 oyster‐associated gastroenteritis outbreaks were examined for the presence of 10 human enteric viruses using antigenic or genetic detection methods in order to determine the prevalence of these infections. All virus‐positive patients were over 18 years old. The most common enteric virus in outbreaks (96.6%) and fecal specimens (68.9%) was norovirus (NoV), indicating a high prevalence of NoV infection associated with the consumption of raw or under‐cooked oysters. Five other enteric viruses, aichiviruses, astroviruses, sapoviruses, enteroviruses (EVs), and rotavirus A, were detected in 30.7% of outbreaks. EV strains were characterized into three rare genotypes, coxsackievirus (CV) A1, A19, and EV76. No reports of CVA19 or EV76 have been made since 1981 in the Infectious Agents Surveillance Report by the National Infectious Diseases Surveillance Center, Japan. Their detection suggested that rare types of EVs are circulating in human populations inconspicuously and one of their transmission modes could be the consumption of contaminated oysters. Rapid identification of pathogens is important for the development of means for control and prevention. The results of the present study will be useful to establish an efficient approach for the identification of viral pathogens in oyster‐associated gastroenteritis in adults. J. Med. Virol. 86:2019–2025, 2014.

Gastroenteritis Outbreaks Caused by a DS-1-like G1P(8) Rotavirus Strain, Japan, 2012-2013

Rotavirus A (RVA) genotype G1P[8], a hallmark of the Wa-like strain, typically contains only genotype 1 genes. However, an unusual RVA G1P[8] with genotype 2 genes was recently detected in Japan. We determined the complete genomic constellation of this RVA. Our findings suggest that mixed RVAs may be more competitive than once thought.

Genotyping of Norovirus strains detected in outbreaks between April 2002 and March 2003 in Osaka City, Japan.

Noroviruses (NVs) are the major cause of food‐ and waterborne nonbacterial gastroenteritis in Japan. Between April 2002 and March 2003, a total of 111 fecal specimens from 40 outbreaks of acute nonbacterial gastroenteritis in Osaka City, Japan were subject to NV detection. Seventy‐two samples (64.9%) from 31 outbreaks (77.5%) were NV positive by a real time reverse transcription (RT)‐PCR assay. To further determine the genotype of individual NV strains, we sequenced the capsid N‐terminal/shell (N/S) domain of some representative strains from each outbreak. The 51 NV strains detected in this study were segregated into 15 genotypes (6 in genogroup I and 9 in genogroup II), and GII/5 genotype NV was a dominant outbreak genotype.

Genetic Analysis of the Capsid Gene of Genotype GII.2 Noroviruses

ABSTRACT Noroviruses (NoVs) are considered to be a major cause of acute nonbacterial gastroenteritis in humans. The NoV genus is genetically diverse, and genotype GII.4 has been most commonly identified worldwide in recent years. In this study we analyzed the complete capsid gene of NoV strains belonging to the less prevalent genotype GII.2. We compared a total of 36 complete capsid sequences of GII.2 sequences obtained from the GenBank (n = 5) and from outbreaks or sporadic cases that occurred in The Netherlands (n = 10) and in Osaka City, Japan (n = 21), between 1976 and 2005. Alignment of all capsid sequences did not show fixation of amino acid substitutions over time as an indication for genetic drift. In contrast, when strains previously recognized as recombinants were excluded from the alignment, genetic drift was observed. Substitutions were found at five informative sites (two in the P1 subdomain and three in the P2 subdomain), segregating strains into five genetic groups (1994 to 1997, 1999 to 2000, 2001 to 2003, 2004, and 2005). Only one amino acid position changed consistently between each group (position 345). Homology modeling of the GII.2 capsid protein showed that the five amino acids were located on the surface of the capsid and close to each other at the interface of two monomers. The data suggest that these changes were induced by selective pressure, driving virus evolution. Remarkably, this was observed only for nonrecombinant genomes, suggesting differences in behavior with recombinant strains.

Co-Infection of Human Metapneumovirus with Adenovirus or Respiratory Syncytial Virus among Children in Japan

Human metapneumovirus (hMPV) is one of the etiological agents of acute respiratory tract infections. From June 2005 to May 2006, we collected 185 clinical specimens from children in Osaka City, Japan, and detected 41 hMPV RNA. Of the 41 specimens, four (9.8%) also contained other viruses (3 with adenovirus [AdV] and 1 with respiratory syncytial virus [RSV]). The clinical symptoms of patients co‐infected with AdV were indistinct from those of patients mono‐infected with hMPV. The symptoms of the one patient co‐infected with RSV were clinically severe. Further research is needed to clarify the effect of hMPV on other respiratory viruses or vice versa.