A parent's guide to shellfish allergies

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A muscle protein, tropomyosin, is the major allergenic factor contained in shellfish. Shellfish includes both crustaceans (shrimp, crab, lobster) and mollusks (clams, mussels, oysters). (AP Photo/Pat Wellenbach)

by Christopher C. Chang, M.D., Ph.D.

Kids (and adults) typically find out they’re allergic to shellfish when they eat it and have a reaction. That is what happened to B.J., 11, of Wilmington, De.

“He’s not a seafood eater, but he tasted shrimp and felt itchy and nauseated, so I thought it possibly didn’t agree with him,” said his mother, LaWann.

It seemed like a small reaction. But later that summer, when B.J. tried crab, his eye, ears and throat felt itchy and LaWann knew that he was indeed allergic to shellfish. B.J. now avoids shellfish and carries epinephrine in the form of an Epi-pen® wherever he goes. Once children have a suspected reaction to shellfish, it’s wise to have them tested by an allergy specialist and if the suspicion is confirmed to get a prescription for the epi-pen to counteract anaphylaxis, hives and swelling.

Unfortunately, it’s relatively rare that children will grow out of a shellfish allergy. Among adults in North America, the most common allergen is shellfish. For children it’s milk, and while kids often outgrow their milk allergies, people who are allergic to shellfish are usually affected for life.  A muscle protein, tropomyosin, is the major allergenic factor contained in shellfish but not in other types of fish. Shellfish includes both crustaceans (shrimp, crab, lobster) and mollusks (clams, mussels, oysters).

What precautions should parents take? For those with a known shellfish allergy, obviously the first line of defense is avoidance. Parents should be cautious in restaurants and ask about food preparation – are fish and shellfish prepared separately? Parents should also be aware of misleading product names and cross-contamination in packaged products. For example, imitation crab is really fish (usually Alaskan Pollack). Therefore, parents should  be vigilant about reading labels. Labeling laws require food allergens to be identified in plain English, even if the product contains a very small amount of any of the “top 8”: Milk, eggs, soy, wheat, peanut, tree nut, fish and shellfish.

Is it possible to react to shellfish without ingesting it? Yes. Shrimp that is boiled or stir-fried, for example, can be aerosolized and trigger a reaction in someone who is highly sensitive to the allergen. In that case, be especially cautious about taking a child to any place where shellfish is being prepared. This is true for seafood allergens, but not typical for other common food allergens, such as nuts or egg.

Can allergies be inherited? Your tendency to develop shellfish allergies is influenced by both genetics and geography. Children with a family history of this type of allergy are more prone to develop it themselves. Seafood allergies are more prevalent in regions where people eat the most fish – in Asia, for example, where two-thirds of the world’s fish is consumed.

Can shellfish allergy be mistaken for food poisoning and vice versa? Yes, people can be sickened by eating seafood, but not necessarily be allergic to it. A toxin in seafood that’s less than fresh can be released, causing nausea and vomiting, which may be mistaken for an allergic reaction. One way to know for sure is to be evaluated by a specialist.

Christopher C. Chang, M.D., Ph.D., is division chief of the division of pediatric allergy/immunology at Nemours/Alfred I. duPont Hospital for Children, and clinical professor of pediatrics at Jefferson Medical College.

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