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Evaluation and Validation of Alternative Indicators of Viral Contamination in Bivalve Molluscan Shellfish

Institutions
Centre for Environment, Fisheries and Aquaculture Sciences (CEFAS)
Start date
2000
End date
2002
Objective
This research project aims to identify viral indicators that may be used to predict the safety of shellfish more effectively than E. coli.

Shellfish transmitted diseases tend to be of viral origin and usually cause outbreaks of gastroenteritis or infectious hepatitis.

The main reason for this is that many bivalve shellfish species, such as oysters and mussels, are produced in shallow, inshore estuaries that are often contaminated with human sewage. Bivalve shellfish are filter feeders.

This means that, in the process of feeding, they can concentrate and retain human pathogens derived from sewage contamination.

The risk to the consumer from the accumulation of human enteric viruses, such as Norovirus (NV) and hepatitis A (HAV) in shellfish, is increased by the fact that many species are eaten raw or lightly cooked, and also because the whole animal is consumed.

Monitoring of the virological quality of shellfish and/or the waters in which they grow would be both desirable and beneficial. However the main viruses of concern, NV and HAV, are non-culturable or very difficult to culture in the laboratory.

Their detection relies upon use of complex molecular methods, which are technically difficult, time consuming, costly, poorly standardised and restricted to a few specialist laboratories.

It is for these reasons that commensal enteric bacteria, such as faecal coliforms and E. coli, have been adopted as surrogate indicator organisms to assess the quality of shellfish flesh and to predict the risk of exposure to enteric pathogenic viruses.

Across the EU, the criteria laying down the microbiological standards for bivalve molluscs are set out in European Directive 91/492/EEC.

These regulations make use of E. coli to assess the faecal contamination of shellfish, to instigate appropriate control measures (e.g. depuration or relaying in clean waters) and to set end product standards.

However, the continuing occurrence of NV and HAV associated diseases linked to the consumption of shellfish that are fully compliant with end product standards suggests that reliance on the traditional faecal indicators does not adequately protect the shellfish consumer.

The project aimed to evaluate and validate the use of viral indicator organisms as alternatives to the recommended microbial contamination indicator, E. coli, in sewage contaminated shellfish and shellfish sold for direct human consumption.

More information
A comprehensive review of existing sources of information was undertaken. This included scrutiny of published scientific/technical journals and analysis of existing in-house data.

This approach allowed the most promising candidate viral indicators to be identified.

The second phase of the research was to optimise methods to detect these viral indicators in the laboratory to permit their application to the complex matrix that constitutes shellfish tissue.

This was followed by the evaluation and validation stage, where selected alternative indicators were tested on 'real' samples during intensive series of field trials.

All samples were analysed for pathogenic viruses (NV and HAV) and E. coli. This allowed the performance of the alternative indicators to be compared both with the current microbiological indicator (E. coli) and the actual pathogens of interest in shellfish harvesting areas and as an endproduct test in shellfish available for human consumption.

Find more about this project and other FSA food safety-related projects at the Food Standards Agency Research webpage.

Funding Source
Food Standards Agency
Project number
B04009
Categories
Bacterial Pathogens
Commodities
Seafood