As more people across the world consume more seafood, shellfish allergies have significantly increased in the last few decades. Allergic reactions can happen when people touch or eat shellfish or breathe in vapors from cooking shellfish. Workers in shellfish-processing plants are also at risk for developing shellfish allergies, reports Dr. A.L. Lopata in the April 2010 issue of "Clinical and Experimental Allergy." Reactions to shellfish can cause symptoms ranging from mild sensitivity to a fatal systemic reaction. There are two major groups of shellfish, each containing different proteins that can elicit allergic reactions: crustaceans and mollusks.
Crustaceans
Crustaceans include shrimp, prawns, crabs, lobster and crayfish. As a group, crustaceans are a frequent cause of anaphylaxis, or hypersensitivity, with shrimp and crab as the most common causes of allergy. According to the American Academy of Allergy, Asthma & Immunology (AAAAI), allergies to multiples types of crustaceans are common, so physicians may caution patients about eating other crustaceans if there is an allergy to one type. Allergies to crustaceans are considered life-long and usually begin in childhood, notes Dr. R.M. Kandyil in the August 2009 issue of "Pediatric Allergy and Immunology." Symptoms usually occur within minutes after eating crustaceans and include itching and swelling of the lips, mouth and throat. Hives, rash and asthma are common allergic reactions to eating crustaceans and may occur with anaphylaxis.
Mollusks
Mollusks include clams, mussels, oysters, scallops, limpets, abalone, squid, cuttlefish and octopuses. Snail, limpet and abalone are the most common causes of molluscan allergy, according to Dr. Steve Taylor in a 2008 issue of "Advances in Food and Nutrition Research." Persons allergic to mollusks may experience nausea, vomiting, abdominal cramps, hives and swelling, asthma and in some cases, anaphylactic shock. Symptoms of molluscan allergy usually appear within minutes up to two hours after eating the offending seafood. Some persons may experience symptoms as late as eight hours after eating snow crab, cuttlefish, limpet and abalone, notes Lopata. Persons allergic to mollusks are considered at risk for exercise-induced anaphylaxis. Persons allergic to mollusks who work at seafood-processing plants are also at risk for developing symptoms when they handle mollusks or inhale dust from mollusk shells.
Cross-reactivity
Cross-reactivity occurs when a person shows allergic responses to an allergen that he is not originally sensitive to. For example, a person allergic to crab usually will have an allergic reaction to other crustaceans. The same is true among mollusks. Cross-reactivity is common within one kind of shellfish, but cross-reactivity between crustaceans and mollusks is not well-described, notes the AAAAI. Therefore, physicians may advise patients to refrain from eating shellfish when an allergy to one type is diagnosed. Crustaceans do not cross-react with fish. But certain shellfish, particularly crustaceans and squid, may cross-react with house dust mites and cockroaches.
References
- "Clinical and Experimental Allergy"; Shellfish Allergy; A.L. Lopata; April 2010
- American Academy of Allergy, Asthma & Immunology; Food Allergy: A Practice Parameter; Jean A. Chapman; March 2006
- "Pediatric Allergy and Immunology": Shellfish Allergy in Children
- "Advances in Food and Nutrition Research": Molluscan Shellfish Allergy; Steve Taylor; 2008
