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

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.Citation: Akter A, Ooka T, Gotoh Y, Yamamoto S, Fujita H, Terasoma F, Kida K, Taira M, Nakadouzono F, Gokuden M, Hirano M, Miyashiro M, Inari K, Shimazu Y, Tabara K, Toyoda A, Yoshimura D, Itoh T, Kitano T, Sato MP, Katsura K, Mondal SI, Ogura Y, Ando S, Hayashi T. Extremely Low Genomic Diversity of Rickettsia japonica Distributed in Japan. Genome Biol Evol. 2017 Jan 1;9(1):124-133. doi: 10.1093/gbe/evw304. PMID: 28057731; PMCID: PMC5381555