Norovirus pathway in water environment estimated by genetic analysis of strains from patients of gastroenteritis, sewage, treated wastewater, river water and oysters

In this study, Norovirus (NV) capsid gene was detected from patients of gastroenteritis, domestic sewage, treated wastewater, river water and cultivated oysters in geographically close areas where all of samples were collected. In order to improve recovery efficiency of NVs from oysters, a new method using a spallation apparatus was developed. As a result, 18 of 30 oysters (60%) were positive for NV gene, while 7 of 30 (23%) oysters from the same sampling point were positive with the conventional ultracentrifugal method between November 2003 and February 2004. These results indicate that our new method exhibits the higher efficiency of recovering NVs than the conventional ultracentrifugal method. Six of 8 samples (75%) of river water were positive for NV gene between November 2003 and February 2004. Furthermore, 8 of 9 samples (89%) of treated wastewater and all 9 samples of sewage were positive for NV gene in the same period. These results indicated that treated wastewater would be one of the main sources for NV pollution in this area. The phylogenetic analysis in isolated NV capsid genes was conducted, in which high identities of gene sequences between NVs from patients, domestic sewage, river water and cultivated oysters were observed. These results implied that there would be a geographically associated circulation of NVs between human and cultivated oysters via water environment. It would be important to quantitatively analyze the moving pathway of NVs, which directly link to the development of a new scheme for preventing water environment and cultivated oysters from NV contamination.