Shellfish includes shrimp, prawn, lobster, crab, clam, oyster and mussel. Shellfish allergy is less common in children than in adults. Children who are allergic to shellfish are usually not allergic to white fish, salmon and tuna.
Symptoms can occur not only after eating shellfish, but also after contact or from breathing the shellfish vapour during cooking or at a fish market. Usually only a hives or “nettle” rash develops. Sometimes as well as a rash, swelling, especially around the face may occur. Some children have an itchy throat; others vomit or can have diarrhoea.
Severe reactions are much less common, but can include difficulty in breathing (with wheeze or swelling in the throat), feeling faint or dizzy. Vapours from the shellfish may trigger an asthma attack in children that are allergic.
Allergic reactions are usually mild. Severe reactions affecting the child’s breathing can occur, particularly in those with bad asthma who need urgent medical attention.
Shellfish allergy can sometimes be confused with shellfish poisoning. This is also called ciguatera poisoning. It occurs in warmer weather because of algae in the water. The poison is not destroyed by cooking the shellfish. It generally occurs in seafood with two shells such as clams, oysters, mussels, and sometimes scallops.
Shellfish and fish are different. People who are shellfish allergic may be able to eat fish. There are two different types of shellfish: mollusks and crustaceans. Mollusks include mussels, clams, oysters, and squid. Crustaceans include prawns, shrimp, lobster, crab, and crayfish. People who are allergic to one type of crustacean, such as prawn, are generally allergic to all other crustaceans but may be able to eat mollusks. Your allergist will be able to advise.
The diagnosis of shellfish allergy is suggested by a history of a reaction after contact with shellfish and a positive skin prick or blood IgE test. An oral challenge is required for a firm diagnosis, as recent evidence suggests that only 10-20% of children with a history of allergy to shellfish and positive allergy tests will react on hospital challenge.
Skin prick tests can be done in clinic provided that the child has not had any antihistamines for a few days. Blood tests are not affected by antihistamines, but the results are only available in a week or so after the clinic appointment.
Shellfish is easy to avoid. Some foods, such as Worcestershire sauce, steak sauce, fried rice, egg rolls, salad dressings, seafood muffaletta sandwiches can have shellfish as hidden ingredients. Cross contamination when buying fresh shellfish over the counter in shops and supermarkets can occur. Some dishes like paella, bouillabaisse, gumbo and frito misto contain lots of different kinds of fish at once, can be difficult to spot. It is useful to avoid such dishes. Some face creams and health supplement can have crushed shells.
After a reaction to shellfish, your child should be provided with advice about what to do if they have another reaction. The plan is usually written down – Allergy Management Plan.
Mild reaction – hives, swelling or vomiting, but no breathing problems or faintness:
If possible, get the child to spit out the food. Give an antihistamine.
Severe reaction – difficulty breathing (wheezing, noisy breathing, blue colour); swelling in the throat (noisy breathing, drooling); feeling faint or dizzy, looking very pale (lie the child down with their legs raised).
Get help straight away and dial 999 stating “anaphylaxis” (ana-fil-ak-sis). If you have an adrenaline pen – use it.
It is important to inform the nursery/school and any after school clubs. Any other carers will also need to know.
Shellfish allergy is usually life-long. If there has been no reaction for a long time an oral challenge may be suggested.
There is no cure for shellfish allergy at present.