Detection and Genetic Analysis of Noroviruses and Sapoviruses in Sea Snail

An outbreak of acute gastroenteritis occurred at a restaurant in Yokohama in December 2011. Because many of the customers had consumed raw sea snail, sea snail was suspected to be the source of this outbreak. To determine whether sea snail contains Norovirus (NoV) or Sapovirus (SaV), we analyzed 27 sea snail samples collected over 5 months (May, June, August, October, and December 2012) and 59.3% were positive for NoV and/or SaV. The levels of NoV ranged from 1.5 × 10(3) to 1.5 × 10(5) copies/g tissue, and those of SaV from 1.5 × 10(2) to 1.3 × 10(3) copies/g tissue. The highest levels were observed in sea snails collected in December. A phylogenetic analysis of the NoVs showed that the viral strains were NoV genotypes GI.4, GI.6, GII.4, GII.12, GII.13, and GII.14, and the SaV strains were genotypes GI.2 and GI.3. The NoV GII.4 Sydney 2012 variants were only detected in December. This variant was a major source of gastroenteritis in Japan in the winter of 2012/2013. In contrast, the NoV GII.4 strains detected in May and June 2012 were not the Sydney 2012 variant. This study demonstrates that sea snail contains multiple genogroups and genotypes of NoV and SaV strains. We conclude that the sea snail presents a risk of gastroenteritis when consumed raw.