Norovirus Accumulation in Wild Estuarine Bivalves and Its Relationship with Gastroenteritis Epidemics

摘要

Previous studies reported heavy contamination of oysters with Norovirus (NoV) excreted by patients of gastroenteritis in the epidemic season, suggesting that monitoring of NoV in oysters is useful for surveillance of epidemic of viral gastroenteritis. This study aimed at continues monitoring of NoV in oysters and clams (Nuttallia japonica) as common estuarine bivalves living in rocky and sandy zones, respectively. From October 2017 to November 2018, twenty samples of each bivalve were collected monthly from an estuary in Sendai, Japan, except the epidemic season (November to March) with twice-a-month sampling. Digestive tissues (DT) isolated from four bivalve samples were composited and NoV-GI and GII were quantitatively detected by qPCR analysis. The result of monitoring demonstrated that NoV concentrations in oysters and clams increased in 2018 epidemic season, while such a seasonality was not found in 2017. In the epidemic season, the NoV-GII concentrations in oysters and clams showed significantly positive correlations with the number of gastroenteritis patients reported in Sendai city one and three weeks before the sampling of bivalves, respectively. This suggests that it takes a longer time for NoV transported from the city by river water to reach clams living in sand than oysters exposed to the water.