As oysters are eaten raw in Japan, their contamination with the non-bacterial agent of gastroenteritis has become a serious health problem. As it is well known that oysters tend to concentrate noroviruses (NV) in their digestive diverticula, NV may be linked with the acute gastroenteritis. However, since NV cannot be cultivated in cell cultures, and they have genetic diversity, the behaviour of NV in the aquatic environment is little known. In this study, NV samples were taken from gastroenteritis patients; from the river flowing into the oyster-farming area; and from oysters harvested from that river. Genetic identities of NV samples were analysed in capsid and RNA-dependent RNA polymerase (RdRp) regions respectively. In both regions, strains taken from patients were >96% identical with those from river and oyster samples. This proved that oysters were contaminated with NV excreted from patients with gastroenteritis.

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