Processing Strategies to Inactivate Enteric Viruses in Shellfish: Limitations of Surrogate Viruses and Molecular Methods

Authors: Richards, Gary; MACLEOD, CATHERINE - University Of South Australia; LE GUYADER, F. - French Research Institute For The Expolotation Of The Sea (IFREMER)

Submitted to: Food and Environmental Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2010
Publication Date: 6/14/2010
Citation: Richards, G.P., Macleod, C., Le Guyader, F.S. 2010. Processing Strategies to Inactivate Enteric Viruses in Shellfish: Limitations of Surrogate Viruses and Molecular Methods. Food and Environmental Virology. Available: doi:10.107/s12560-010-9045-2.

Interpretive Summary: Oysters, clams and mussels are an important cause of food-related viral illness. Viruses, like hepatitis A virus, norovirus, adenovirus, rotavirus and others can lead to illness when shellfish are contaminated in their natural environments with sewage, or when shellfish are handled or processed in an unsanitary manner. This paper discusses: a) mechanisms that shellfish use to concentrate viruses from seawater within their edible tissues, b) methods to reduce virus contamination of shellfish through the use of approved shellfish harvesting and handling practices, c) the effectiveness of various processing techniques to inactivate infectious viruses in shellfish, d) limitations in current testing procedure, and e) recommendations for future research. Processing methods include: cooking and heat pasteurization; freezing; irradiation; high pressure processing; the commercial process of shellfish depuration, where shellfish are placed in tanks of clean seawater to purge contaminants over a short period; and shellfish relaying, where shellfish are transplanted from marginally polluted shellfish beds to clean seawater to purge contaminants over a long period. Although these methods can improve shellfish safety, none have been demonstrated to totally eliminate infectious viruses without some decrease in shellfish quality.

Technical Abstract: Noroviruses, hepatitis A and E viruses, sapovirus, astrovirus, rotavirus, Aichi virus, enteric adenoviruses, poliovirus, and other enteroviruses enter shellfish through contaminated seawater or by contamination during handling and processing, resulting in outbreaks ranging from isolated to epidemic. Processing and disinfection methods include shellfish depuration and relaying, cooking and heat pasteurization, freezing, irradiation, and high pressure processing. All methods can improve shellfish safety; however, from a commercial standpoint, none of the methods can guarantee total virus inactivation without impacting the organoleptic qualities of the shellfish. Noroviruses cause the majority of foodborne viral illnesses, yet there is conflicting information on their susceptibility to inactivation by processing. The inability to propagate and quantitatively enumerate some viral pathogens in vitro or in animal models has led to the use of norovirus surrogates, such as feline calicivirus and murine norovirus. During processing, these surrogates may not mimic the inactivation of the viruses they represent and are, therefore, of limited value. Likewise, reverse transcription-PCR has limited usefulness in monitoring processing effectiveness due to its inability to identify infectious from inactivated viruses. This paper: a) describes mechanisms of virus uptake and persistence in shellfish, b) reviews the state-of-the-art in food processing strategies for the inactivation of enteric viruses in shellfish, c) suggests the use of combined processing procedures to enhance shellfish safety, d) highlights limitations in research data derived from virus surrogate studies and molecular assay procedures, and e) recommends enhanced funding for human volunteer studies and the development of assays to detect viable viruses.