Diversity of emerging GII.17 norovirus strains in shellfish linked to outbreaks

Norovirus epidemics linked to shellfish consumption are among the most frequently recognised causes of foodborne gastroenteritis. Norovirus (NoV) are positive-strand RNA viruses with a large genetic diversity. 25 different NoV... [ view full abstract ]

Norovirus epidemics linked to shellfish consumption are among the most frequently recognised causes of foodborne gastroenteritis. Norovirus (NoV) are positive-strand RNA viruses with a large genetic diversity. 25 different NoV genotypes are known to infect humans, most of them belonging to genogroups I (GI) and II (GII). For the past 20 years, pandemic strains from the GII.4 genotype were implicated in most human cases, and very frequent in shellfish-borne outbreaks. Since the winter 2014-2015, emerging strains from the GII.17 genotype are dominant in Asia and spreading worldwide. They were detected in sewage and oysters in Japan, and in an oyster-related outbreak in Denmark. Yet, little is known on the frequency of these emerging GII.17 strains in shellfish and shellfish-related outbreaks in Europe, or on their bioaccumulation efficiency and selection by shellfish.

We analyzed shellfish (mussel and oyster) samples linked to confirmed NoV outbreaks in France between January and March 2016. Using a classical sequencing approach on cloned PCR products, we identified the GII.17 genotype in all samples. We gained better insight into the diversity of NoV strains in these samples, by applying a metabarcoding approach with MySeq deep sequencing on PCR products. The bioaccumulation efficiency of the emerging GII.17 strain was compared to that of GI.1 and GII.4 genotypes in oysters, and showed similar tissue distribution and enrichment levels. Together these results show that the emerging dominant strain GII.17 is efficiently bioaccumulated in shellfish and is likely to pose a threat comparable to that of GII.4 on shellfish consumption.