Allergy to shellfish (crustaceans and molluscs) is more common among adults than among children. Skin reactions like urticaria, edema and eczema are the most frequent symptoms in shellfish allergy, followed by gastrointestinal symptom. Respiratory symptoms like asthma have also been reported. A number of reports of severe reactions triggered by crustaceans can be found in the literature.
Asthma caused by inhalation of dust from shellfish as well as eczema from handling of shellfish during processing has been reported.
Crustacean allergic subjects commonly react both to shrimp, crab, lobster and crayfish. Many also react to molluscs like abalones, mussels, oysters, scallops, clams or octopus, squid and cuttlefish. Even reactions to snails have been reported among those with allergy to crustaceans. Surimi products are commonly produced from fish but may contain a certain amount of crab meat.
Labeling
The presence of crustaceans and products thereof as well as molluscs and products thereof in food products must always be declared, see further in LIVSFS 2004:27 Livsmedeslverkets föreskrifter om märkning och presentation av livsmedel [in Swedish] (see link to the right).
Example of methods of analysis
Tropomyosin is the major allergen in shrimps and other crustaceans. The protein is heat stable and thus suitable for analysis of crustaceans in food samples.
Commercial test kits, i.e. ELISAs are available for the analysis of shellfish protein/tropomyosin. The limit of quantification is about 0.5-1 mg shellfish protein/kg, somewhat depending on the matrix.
Shellfish protein/tropomyosin can be detected in food samples using rapid methods, based on test strips, which are soaked in an extract of the food. Such tests are only qualitative, i.e. the result is given either as tropomyosin is present (positive) or tropomyosin is not present (not detected) in the food extract. Positive results need sometimes to be confirmed with quantitative methods. It is very important that qualitative test kits don’t give false negative results.
Providers of test kit often have a validation protocol to be submitted with the test kit upon request. Laboratories using commercial test kits must establish in house control of limit of detection and limit of quantification in actual matrices, even if the test has been validated by the provider.
Allergic reactions/ doses
There is little information about the lowest dose of shellfish or shellfish protein that can cause an allergic reaction. Reactions to 14 g of shrimps were reported in one study, in another provocation study 16 g of shrimps caused clinical symptoms. The protein dose is estimated to be below 32 mg.