Mayumi Obara

Continuous presence of noroviruses and sapoviruses in raw sewage reflects infections among inhabitants of Toyama, Japan (2006 to 2008).

ABSTRACT Various genotypes of norovirus (NoV) (genogroup I genotype 1 [GI.1], -2, -4, -5, -8, -11, -12, and -14; GII.3, -4, -6, -7, -10, -13, -14, and -15), and sapovirus (SaV) (GI.1 and GI.2, GII.1, and GIV.1) were detected from raw sewage from April 2006 to March 2008, while limited numbers of genotypes of NoV (GI.8, GII.4, GII.6, and GII.13) and SaV (GII.3 and GIV.1) and of NoV (GII.4, GII.7, and GII.13) were detected from clinical cases and healthy children, respectively. During the winter 2006 to 2008, a large number of sporadic gastroenteritis outbreaks and many outbreaks caused by NoV GII.4 occurred among inhabitants in Toyama, Japan. The copy number of genomes of NoV GII detected from raw sewage changed in relation to the number of outbreaks. NoV strains of the same genotypes observed in both raw sewage and human specimens belonged to the same cluster by phylogenetic analysis and had almost identical nucleotide sequences among each genotype. These data suggest that NoVs and SaVs detected from raw sewage reflect the viruses circulating in the community, irrespective of symptoms, and that subclinical infections of NoV are common in Japan. Combined surveys of raw sewage with those of clinical cases help us to understand the relationship between infection of these viruses and gastroenteritis.

Frequent Detection of Noroviruses and Sapoviruses in Swine and High Genetic Diversity of Porcine Sapovirus in Japan during Fiscal Year 2008

ABSTRACT A molecular biological survey on porcine norovirus (NoV) and sapovirus (SaV) was conducted in Toyama Prefecture, Japan, during fiscal year 2008. Both NoV and SaV were detected from swine fecal samples throughout the surveillance period, indicating that these viruses were circulating in this region. NoV strains detected in this study belonged to three genotypes that are known as typical swine NoVs. Although human NoVs were occasionally detected, it was unclear whether they replicated in pigs. As for SaV, genogroup VII (GVII) and other divergent genogroups were identified in addition to the dominant genogroup, GIII, which is the prototypic porcine SaV. In addition, 3 strains genetically related to human SaV were detected. Two of these 3 strains were closely related to human SaV GV. Our study showed that genetic diversification of porcine SaV is currently progressing in the swine population.

Enzyme-linked immunosorbent assay using recombinant antigens expressed in mammalian cells for serodiagnosis of tick-borne encephalitis.

A recombinant plasmid that expresses the tick-borne encephalitis (TBE) virus premembrane (prM) and envelope (E) proteins in mammalian cells was constructed. Recombinant proteins retained antigenic and conformational structures similar to those of native virus proteins, and transfected cells released virus-like particles (VLPs), which were 1.13-1.14 g/ml in density and 20-30 nm in diameter, into the culture medium. Recombinant E proteins were used for the development of an enzyme-linked immunosorbent assay (ELISA) to detect TBE virus-specific IgM and IgG antibodies in serum. The results of this ELISA correlated well with the results of commercial ELISA, when tested with 95 serum samples from clinically TBE-suspected patients. In addition, ELISA using recombinant antigens showed no cross-reactivity against serum from Japanese encephalitis (JE) patients, despite the cross-reactivity shown by commercial ELISA systems. These observations indicated that this newly developed ELISA system could distinguish tick-borne encephalitis from Japanese encephalitis infection, and that it constitutes a useful and safe alternative to conventional ELISA systems.

Single Base Substitutions in the Capsid Region of the Norovirus Genome during Viral Shedding in Cases of Infection in Areas Where Norovirus Infection Is Endemic

ABSTRACT Norovirus (NoV) infections are the major cause of food- and waterborne nonbacterial gastroenteritis in Japan. Some individuals showed long-term excretion of the virus into feces in 29 outbreaks of acute nonbacterial gastroenteritis that occurred in Toyama Prefecture, Japan, in fiscal year 2006. In one of these cases, single base substitutions from A to G in the capsid region of the NoV genome were commonly detected in two individuals during virus shedding by direct sequencing of PCR products. The A-to-G substitution was accompanied by an N-to-S amino acid change. The population of clones that possessed A at the corresponding site was gradually replaced by those with G during the infectious course. Although other substitutions were observed in the complete open reading frame 2 sequence, they were not common in these two individuals. NoVs are capable of evolving in the gastroenteric tract.

Development of an ELISA system for tick-borne encephalitis virus infection in rodents

Tick‐borne encephalitis (TBE) virus causes severe encephalitis with serious sequelae in humans. An epizootiological survey of wild rodents is effective to detect TBE virus‐endemic areas; however, limited serological diagnostic methods are available to detect anti‐TBE virus antibodies in wild rodents. In this study, ELISAs for the detection of rodent antibodies against the TBE virus were developed using two recombinant proteins, domain III of the E protein (EdIII) and subviral particles (SPs), as the antigens. As compared with the neutralization test, the ELISA using EdIII had 77.1% sensitivity and 80.0% specificity, and the ELISA using SPs had 91.4% sensitivity and 100% specificity. Furthermore, when the ELISAs were applied to the epizootiological survey in the TBE virus‐endemic area, both of the ELISAs was able to detect wild rodents with TBE virus‐specific antibodies. This is the first study to show that ELISAs using recombinant antigens can be safe and useful in the detection of TBE virus‐infected wild rodents in epizootiological research.

Evaluation of a two-dose administration of live oral poliovirus vaccine for wild and virulent vaccine-derived poliovirus type 1, 2, 3 strains in Japan

We evaluated the efficacy of Japans vaccination policy, a 2-dose administration of live oral poliovirus vaccine (OPV) against wild and virulent vaccine-derived poliovirus (VDPV) type 1, 2, 3 strains, by investigating the neutralizing antibody titers of residents in Toyama Prefecture, Japan. Seropositivities against the virulent type 1 and 2 strains were more than 90%, but the values against the virulent type 3 strains were approximately 60%. Also, while geometric mean antibody titers against virulent type 1 and 2 strains were more than 180, those against the virulent type 3 strains were 58–59, and 9–12, in particular, at 10 to 19 y of age. A booster dose of the vaccine for the type 3 virus is recommended for adolescents. However, high herd immunity against type 1, 2 and 3 viruses has been maintained for these 22 y, although the seropositivity against type 3 virus was always lower than other types. Our results suggest that Japans vaccination policy might be enough to prevent an epidemic of poliomyelitis caused by wild and virulent VDPV type 1, 2, 3 strains, even though the titers against type 3 viruses were the lowest.