Molluscs are a large and diverse group, which includes some 100,000 species living in salt water, in freshwater and on land. Molluscs are used as an added ingredient in some processed foods like soups and sauces and in products like surimi.
Case reports and patient series indicate that several molluscs, such as. snail, oyster, clams, mussels, squid, abalone and octopus, can cause food allergic reactions, some of them life-threatening.
The prevalence of self-reported mollusc allergy ranges from about 0.15 per cent in school children in France to about 0.4 per cent or 20 per cent of all seafood allergic cases, in a household survey of 14,948 individuals in the US.
The European Food Safety Authority (EFSA) yesterday released a scientific opinion indicating that mollusc allergenicity is not reliably reduced by food processing.
Tropomyosin allergenicity is heat-resistant, an EFSA panel found. A major allergen of most molluscs is the abundant muscle protein tropomyosin, which is found in several species.
"Although the allergenicity of some other mollusc allergens appears to be destroyed by heat treatment, there are also reports of increased allergenicity after heating," EFSA stated.
Tropomyosin is also found in crustaceans, dust mites, and cockroach and other insectsIn addition to tropomyosin, there is evidence that molluscs contain a number of other allergens, but these are poorly defined so far by scientific studies.
There is little information on the lowest dose of mollusc allergen that can cause a clinical reaction. In one double blind placebo controlled food challenge study with dried snail reactions were observed in the low hundred-mg range, an EFSA scientific panel found.
Annex IIIa of Directive 2000/13/EC, as amended by Directive 2003/89/EC, establishes a list of ingredients that are known to trigger allergies or intolerances.
The directive states that whenever the listed ingredients are used in the production of foodstuffs they must be labelled. The same directive also requires that the list of labelled allergens should be updated on the basis of the most recent scientific knowledge and on the basis of a scientific opinion given by EFSA.
The scientific opinion on molluscs was made at the request of the European Commission, which wants to know whether to include them and their eventual derived products in the list of food allergens that must be labelled on products.