Seafood allergy

What are the allergens?

Very few allergens of seafoods have been characterised, according to the medical and scientific literature. The best known allergens in seafood are the Allergen M from cod fish, and the major allergen found in crustacea. In the group of molluscs, very recently a new allergen from South African, Abalone (Perlemoen) has been found. All of these allergens are very stable and are not destroyed by cooking. As yet it has not been ascertained if some or all of these allergens are responsible for the fact that some patients are allergic to different seafood species in the different groups at the same time (possibly due to cross-allergenicity).

What are the symptoms of seafood allergy?

Reactions are reported to be mostly within 2 hours after ingestion or handling of seafood, or even inhaling cooking vapours. Reactions can also be delayed for up to 6 hours, as has been frequently reported for species of the Mollusc groups such as Abalone and squid. The more common symptoms include skin-, stomach- and respiratory problems. Respiratory problems are very common in sensitive subjects following inhalation of fish or crustacean vapours, such as from cooking.

How is seafood allergy diagnosed?

A precise and detailed patient history and food history is very important in the diagnosis of allergy to seafood to indicate if a reaction is really an allergy or rather caused by a toxin in the food. Information regarding the suspected offending seafood species is very important, but it often fails to provide adequate information. This is often because of the confusion about the common name used for different seafood species in South Africa (e.g. "Rock Lobster" versus "Crayfish") or deceptive marketing practices (seven different tuna species have been labelled as "Tuna"). The clinical evaluation should be supported by the CAP RAST test performed at a laboratory on a small blood sample. In the case of a negative CAP RAST test result, a skin test with extracts of the suspected seafood species can give additional information. In Southern Africa we have many seafood species which are not found in Europe or the United States. This can mean that commercial tests are not available. Therefore, we at UCT Allergology Unit have improved the diagnostic process by developing and using in-house RAST tests and Western Blot tests and skin tests with locally important seafood allergens.

What is to be done?

Patients have to know that seafood allergies tend to persist for several or more years.

It is recommended that patients with a confirmed allergy to a certain seafood are also tested for other species (e.g. con-current crustacean and mollusc allergy is common).

Avoid any possible direct or indirect exposure to the offending seafood species including handling or inhaling cooking vapours.

Take care if eating out as some foods could have been in contact with the offending seafood species (e.g. french fries and fish may be prepared in the same oil), or the seafood species is improperly named (e.g. freshwater Crayfish versus Rock lobster "Kreef").

Wear a Medic Alert badge and very sensitised patients should also carry an injectable adrenaline syringe.