Foodborne Outbreaks Caused by Human Norovirus GII.P17-GII.17-Contaminated Nori, Japan, 2017.

Seven foodborne norovirus outbreaks attributable to the GII.P17-GII.17 strain were reported across Japan in 2017, causing illness in a total of 2,094 persons. Nori (dried shredded seaweed) was implicated in all outbreaks and tested positive for norovirus. Our data highlight the stability of norovirus in dehydrated food products.

Phylogenetic and Geographic Relationships of Severe Fever With Thrombocytopenia Syndrome Virus in China, South Korea, and Japan.

BACKGROUND: Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne acute infectious disease caused by the SFTS virus (SFTSV). SFTS has been reported in China, South Korea, and Japan as a novel Bunyavirus. Although several molecular epidemiology and phylogenetic studies have been performed, the information obtained was limited, because the analyses included no or only a small number of SFTSV strains from Japan. METHODS: The nucleotide sequences of 75 SFTSV samples in Japan were newly determined directly from the patients' serum samples. In addition, the sequences of 7 strains isolated in vitro were determined and compared with those in the patients' serum samples. More than 90 strains that were identified in China, 1 strain in South Korea, and 50 strains in Japan were phylogenetically analyzed. RESULTS: The viruses were clustered into 2 clades, which were consistent with the geographic distribution. Three strains identified in Japan were clustered in the Chinese clade, and 4 strains identified in China and 26 in South Korea were clustered in the Japanese clade. CONCLUSIONS: Two clades of SFTSV may have evolved separately over time. On rare occasions, the viruses were transmitted overseas to the region in which viruses of the other clade were prevalent.

A Cluster of Japanese Spotted Fever Cases Associated with Cemetery Visits in Wakayama City, Japan.

Japanese spotted fever (JSF) is a tick-borne rickettsiosis caused by Rickettsia japonica. Although the number of JSF cases has been increasing, exceeding 300 per year since 2017, clusters of cases are rare. Here, we report a cluster of seven JSF cases, the first nonfamilial cluster of the disease documented in the Japanese literature, and describe the management of the outbreak through prompt investigation and control-and-prevention measures performed collaboratively by members from the clinical, laboratory, and public health fields. All seven cases in the cluster had visited a cemetery in September or October of 2019. R. japonica was detected in whole-blood and/or skin samples from six patients and in the larvae of Haemaphysalis hystricis collected in a field survey. The evidence suggested that this cluster of cases was caused by the conjunction of two circumstances within a short period of time: an increase in the number of visitors to a cemetery during a Buddhist event and an increase in the number of infectious tick larvae in the cemetery through hatching (vertical transmission from infected females). Delays in the treatment of JSF can lead to severe manifestations. Early interventions through collaborative efforts among members from the clinical, laboratory, and public health fields are important for controlling outbreaks, raising the awareness of the public, and diagnosing and treating patients.

First Case Report of Possible Sarcocystis truncata-induced Food Poisoning in Venison.

Along with the increase in consumption of raw animal meat, the prevalence of food poisoning is increasing. A 67-year-old Japanese man had eaten raw venison 4 hours prior to the beginning of vomiting. Many white cysts were discovered in the venison, with numerous bradyzoites being detected after the cysts were punctured. The presence of the Sarcocystis spp. 18S rRNA gene was detected by polymerase chain reaction, and Sarcocystis truncata was isolated from the venison. Sarcocystis truncata has not previously been identified in sika deer (Cervus nippon) in Japan. This is the first report of possible Sarcocystis truncata-induced food poisoning following consumption of venison.

Evolutionary Analysis of the VP1 and RNA-Dependent RNA Polymerase Regions of Human Norovirus GII.P17-GII.17 in 2013-2017.

Human norovirus (HuNoV) GII.P17-GII.17 (Kawasaki2014 variant) reportedly emerged in 2014 and caused gastroenteritis outbreaks worldwide. To clarify the evolution of both VP1 and RNA-dependent RNA polymerase (RdRp) regions of GII.P17-GII.17, we analyzed both global and novel Japanese strains detected during 2013-2017. Time-scaled phylogenetic trees revealed that the ancestral GII.17 VP1 region diverged around 1949, while the ancestral GII.P17 RdRp region diverged around 2010. The evolutionary rates of the VP1 and RdRp regions were estimated at ~2.7 × 10-3 and ~2.3 × 10-3 substitutions/site/year, respectively. The phylogenetic distances of the VP1 region exhibited no overlaps between intra-cluster and inter-cluster peaks in the GII.17 strains, whereas those of the RdRp region exhibited a unimodal distribution in the GII.P17 strains. Conformational epitope positions in the VP1 protein of the GII.P17-GII.17 strains were similar, although some substitutions, insertions and deletions had occurred. Strains belonging to the same cluster also harbored substitutions around the binding sites for the histo-blood group antigens of the VP1 protein. Moreover, some amino acid substitutions were estimated to be near the interface between monomers and the active site of the RdRp protein. These results suggest that the GII.P17-GII.17 virus has produced variants with the potential to alter viral antigenicity, host-binding capability, and replication property over the past 10 years.

Extremely Low Genomic Diversity of Rickettsia japonica Distributed in Japan.

Rickettsiae are obligate intracellular bacteria that have small genomes as a result of reductive evolution. Many Rickettsia species of the spotted fever group (SFG) cause tick-borne diseases known as "spotted fevers". The life cycle of SFG rickettsiae is closely associated with that of the tick, which is generally thought to act as a bacterial vector and reservoir that maintains the bacterium through transstadial and transovarial transmission. Each SFG member is thought to have adapted to a specific tick species, thus restricting the bacterial distribution to a relatively limited geographic region. These unique features of SFG rickettsiae allow investigation of how the genomes of such biologically and ecologically specialized bacteria evolve after genome reduction and the types of population structures that are generated. Here, we performed a nationwide, high-resolution phylogenetic analysis of Rickettsia japonica, an etiological agent of Japanese spotted fever that is distributed in Japan and Korea. The comparison of complete or nearly complete sequences obtained from 31 R. japonica strains isolated from various sources in Japan over the past 30 years demonstrated an extremely low level of genomic diversity. In particular, only 34 single nucleotide polymorphisms were identified among the 27 strains of the major lineage containing all clinical isolates and tick isolates from the three tick species. Our data provide novel insights into the biology and genome evolution of R. japonica, including the possibilities of recent clonal expansion and a long generation time in nature due to the long dormant phase associated with tick life cycles.