Scientific Alert Note

Reducing risk of viral contamination in shellfish

Bivalve shellfish such as oysters can become contaminated by microbiological pathogens when grown in contaminated harvesting areas. It is the aim of the project 3.2 REDRISK to identify pollution sources and conditions responsible for the contamination in order to reduce the risks of harvesting polluted shellfish. The researchers have observed how heavy rainfall may increase the risk of contamination as it may cause overflow in sewage treatment plants thus causing increased feacal input and consequently increased viral discharge to the marine environment. Measurement of change in salinity at a given location may constitute a simple monitoring possibility.

 

Authors: Monique Pommepuy, Ifremer, France, and Bill Doré, Marine Institute, Ireland

 

Sampling and environmental data gathering in a shellfish site on the West Coast of Ireland

Sources of viral contamination can be varied and include both human and agricultural input. Where contaminated shellfish are consumed raw or lightly cooked, this represents a significant health risk for consumers.

Contamination with viruses from human sources, in particular sewage outfalls, is probably the most significant of these risks. Despite extensive controls outbreaks of gastroenteritis and hepatitis A have both been associated with shellfish consumption. The REDRISK project is increasing the knowledge of factors responsible for virus contamination and leading research into procedures for controlling the risk.   

 

During the project a number of environmental factors have been monitored to establish their viral impact on shellfisheries in four  European countries.

 

Using state of the art virus testing methods, results have shown clear links with viral contamination in shellfish and changes in environmental conditions in one of the areas investigated. Two high rainfall events in the region showed significant correlation with the appearance of virus in oysters in an harvest area which was otherwise shown to be largely free of virus throughout the study. Virus levels appeared to be very low and the real significance of the associated risk thus remains unclear.

 

Despite this, the ability to identify site-specific environmental risk factors may pave the way forward for using sophisticated programmes for continuous monitoring of environmental factors such as salinity or rainfall to trigger real-time management action in shellfisheries. This could include temporary suspension of harvesting or increased treatment practices.

Viral analyses in the laboratory

Although major challenges remain given the complex environmental and hydrographic diversity associated with the many shellfisheries throughout Europe, results from the REDRISK project may provide a significant step towards increasing levels of food safety for European consumers of bivalve shellfish.

 

Next steps will be to develop tools which can be applied to real-time monitoring of the significant environmental factors which may lead to viral contamination and to develop site-specific triggers. To this end partners in France are already trialling sensors for continuous remote monitoring of salinity levels in estuaries to predict deterioration in water quality associated with high rainfall. The aim is to develop systems to send automatic alerts when salinity levels fall below trigger levels which could prompt management actions.