Relevance of F-specific RNA bacteriophages in assessing human norovirus risk in shellfish and environmental waters

Abstract

Human noroviruses (HuNoVs) are the main cause of shellfish-borne gastroenteritis outbreaks. In the absence of routine technical approaches allowing infectious particles to be detected, this viral pathogen is currently targeted by genome research, leading to difficult interpretations. In this study, we investigated the potential of F-specific RNA bacteriophages (FRNAPH) as fecal and viral contamination indicators in shellfish and water from a local harvesting area. FRNAPH were also used as microbial source tracking tools. Constraints imposed by detection limits are illustrated here by the detection of infectious FRNAPH in several samples in the absence of FRNAPH genomes. The opposite situation was also observed, likely explained by the persistence of the genomes being greater than infectivity. Similar considerations may be applied to HuNoVs, suggesting that HuNoV genome targeting is of limited relevance in assessing infectious risks. While FRNAPH did not provide any benefits compared to Escherichia coli as fecal pollution indicators in water, novel observations were made in shellfish: Contrary to E. coli, a seasonal trend of infectious FRNAPH concentrations was observed. These concentrations were higher than those found in water, confirming bioaccumulation in shellfish. This study also underlines a relationship between the presence of HuNoV genomes and those of humanspecific FRNAPH subgroup II (FRNAPH-II) in shellfish collected throughout Europe. Further research should be undertaken to evaluate FRNAPH potential as an indicator of the presence of infectious HuNoVs. To this end, shellfish involved in HuNoVcaused gastroenteritis outbreaks should be analyzed for the presence of infectious FRNAPH-II.