cOyster contamination by noroviruses is an important health and economic problem. The present study aimed to compare the behaviors of Norwalk virus (the prototype genogroup I norovirus) and two culturable viruses: Tulane virus and mengovirus. After bioaccumulation, tissue distributions were quite similar for Norwalk virus and Tulane virus, with the majority of viral particles detected in digestive tissues, while mengovirus was detected in large amounts in the gills and mantle as well as in digestive tissues. The levels of persistence of all three viruses over 8 days were comparable, but clear differences were observed over longer periods, with Norwalk and Tulane viruses displaying rather similar half-lives, unlike mengovirus, which was cleared more rapidly. These results indicate that Tulane virus may be a good surrogate for studying norovirus behavior in oysters, and they confirm the prolonged persistence of Norwalk virus in oyster tissues. Shellfish are filter feeders that can accumulate different types of pathogens from human fecal pollution and were identified as vectors for human enteric pathogen transmission more than a century ago. We have known for almost 40 years that bacteria and viruses show differences in terms of concentration and accumulation in and depuration from contaminated shellfish (1). Nowadays the problem of viral contamination has become dominant, and over the last 10 years about 40% of RASFF (Rapid Alert System for Food and Feed) notifications are related to the detection of norovirus (NoV) in oysters (2). Improvements in detection methods, increased epidemiological surveillance, and efforts by authorities to improve the quality of products put on the market have contributed to better recognition of viral contamination. These improvements have assisted in identifying that increases in human populations in coastal areas, as well as climate change, inducing heavy rainfall and associated sewage overflows, constitute risk factors for shellfish contamination (3, 4).Among human enteric viruses, NoVs are recognized as the leading cause of epidemics and sporadic cases of gastroenteritis in all age groups of humans (5, 6). NoVs of human origin are excreted in large quantities by ill people, but they may also be present in asymptomatic, healthy individuals (7). As a consequence, they are discharged in large numbers into sewage, and due to their resistance to inactivation, they are frequently detected in wastewater treatment plant effluent and in surface waters (8-10). Sewage treatment which incorporates new technologies, such as membrane filtration, contributes to decreasing the numbers of microorganisms discharged into the coastal environment (11, 12), but this does not prevent accidental contamination. Depuration of shellfish, which was developed to eliminate bacteria, does not efficiently eliminate viruses that persist for several weeks or months in bivalve tissues (13,14). As a consequence, in most cases of contamination, the only risk management option to prevent consumer infections is the clo...

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