What makes shellfish allergy

In kitchens, shellfish can get into a food product because the staff use the same surfaces, utensils like knives, cutting boards, or pans , or oil to prepare both shellfish and other foods. This is particularly common in seafood restaurants, so some people find it safer to avoid these restaurants. Shellfish is also used in a lot of Asian cooking, so there's a risk of cross-contamination in Chinese, Vietnamese, Thai, or Japanese restaurants.

When eating at restaurants, it may be best to avoid fried foods because many places cook chicken, French fries, and shellfish in the same oil. When eating away from home, make sure you have an epinephrine auto-injector with you and that it hasn't expired. Also, tell the people preparing or serving your child's food about the shellfish allergy. Sometimes, you may want to bring food with you that you know is safe.

Don't eat at the restaurant if the chef, manager, or owner seems uncomfortable with your request for a safe meal. Also talk to the staff at school about cross-contamination risks for foods in the cafeteria. It may be best to pack lunches at home so you can control what's in them. Reviewed by: Stephen F. Dinetz, MD. Larger text size Large text size Regular text size.

What Is a Shellfish Allergy? Shellfish fall into two different groups: crustaceans , like shrimp, crab, or lobster mollusks , like clams, mussels, oysters, scallops, octopus, or squid Some people with shellfish allergies are allergic to both groups, but some are allergic only to one.

This can cause symptoms such as: wheezing trouble breathing coughing hoarseness throat tightness belly pain vomiting diarrhea itchy, watery, or swollen eyes hives red spots swelling a drop in blood pressure, causing lightheadedness or loss of consciousness passing out Allergic reactions to shellfish can differ. Other things to keep in mind: Make sure the epinephrine auto-injector is always on hand and that it is not expired.

Don't feed your child cooked foods you didn't make yourself or anything with unknown ingredients. Tell everyone who handles the food — from relatives to restaurant staff — that your child has a shellfish allergy.

Speak to your doctor about cross-reactivity because it is difficult to predict. The list of fish that can cause an allergic reaction is quite long and includes, but is not limited to:. The list of shellfish including molluscs and crustaceans that can cause allergic reactions includes, but is not limited to:.

The Healthy Eating Advisory Service has more comprehensive lists of seafood that can cause an allergic reaction in some people. Visit your doctor for more information.

If you have allergic symptoms, visit your family doctor, who will ask some questions about your allergic reactions. You can also discuss your record of symptoms.

To diagnose your allergy, your doctor may refer you to a specialist doctor known as an allergist or clinical immunologist. Allergists can test for allergies using a number of methods depending on the type of potential allergy. To test for an allergy to shellfish or fish, the allergist may:. A number of methods claim to test for allergies, but they have not been medically or scientifically proven. They can be costly and could lead to dangerous avoidance of certain foods.

The Australasian Society of Clinical Immunology and Allergy ASCIA , the organisation representing allergists in Australia, recommends that you do not use certain methods to have potential allergies tested.

These methods include:. Always speak with your doctor if you are thinking of using a complementary medicine or therapy to test for allergies. The only current treatment for food allergies is to avoid the food that causes your allergy. Even if you are careful, it is difficult to avoid all contact with a specific food. To help with food avoidance, people with food allergies need to become familiar and comfortable with reading food labels.

ASCIA has fact sheets to help you understand how to read food labels and what to avoid if you have a shellfish or fish allergy. Inaccurate diagnosis can lead to expensive and ineffective treatments, and unnecessary food avoidance that can lead to malnutrition and food aversion, especially in children. Always speak to your doctor about your food allergy diagnosis and treatment options. Emergency responses for a severe allergic reaction are:. Sarcoplasmic calcium binding proteins SCBPs are also members of the EF hand calcium binding protein family incorporating the helix-loop-helix motif in the primary amino acid sequence.

It has a molecular weight of approximately 20 kDa and an isoelectric point of 5, and can elicit IgE binding even after heat treatment [ 22 ]. Recent studies have highlighted the relevance of SCBP as a shellfish allergen. Ayuso et al. Troponin C TnC has been characterized in shrimps, but also as important cockroach allergen Bla g 6 and Per a 6. Troponin C is approximately 20 kDa in size and its possible heat stability is not fully understood.

It has an approximate molecular weight of 28 kDa and is probably heat sensitive [ 29 ]. The clinical and immunological cross-reactivity of TIM among various invertebrate species are not well understood and amino acid sequences have not been performed. True sensitization to shellfish specific allergens can be hampered due the highly cross-reactive nature of some allergenic proteins. The most well known pan-allergen is tropomyosin, being the major cause for reported clinical cross-reactivity among and between crustaceans and mollusks, but also other invertebrates, including mites, cockroaches, and parasites Fig.

It is known that tropomyosin has mainly linear IgE epitopes and is of great importance in determining the degree of cross-reactivity between different shellfish species. Therefore, IgE cross-reactivity is very frequent among crustacean species [ 30 , 31 , 32 , 33 , 34 ].

Graphical representation of immunological cross-reactivity among crustacean and mollusk sp cies as well as to mites, insects, and nematodes.

Within the mollusk group, hypersensitivity cross-reaction is often seen in allergic individuals, as determined for ten different species of cephalopods [ 35 ]. Increasingly important seems to be IgE cross-sensitization between tropomyosin from shellfish and other important allergenic invertebrates, including dust-mites and cockroaches Fig.

It was demonstrated that IgE against mite tropomyosin Der p 10 reacted very strongly to shrimp tropomyosin, although tropomyosin is present in very low concentrations in house dust mites [ 37 ]. More interestingly, reactivity to shrimp has been demonstrated in subjects with house dust-mite allergy, who have never been exposed to shrimps due to religious eating habits [ 38 ].

Applying single allergenic molecules from shellfish for allergen-specific IgE detection could potentially modify. The listed advantages of component-resolved diagnosis CRD require some allergen-related knowledge about. Specific IgE to TM, thanks to its high abundance and stability, is picked up reasonable easily using heated protein extracts from probably most shellfish species. Thus, there is no particular need to further increase test sensitivity. However, increased analytical specificity of TM in molecular-based serological tests will help to identify patients at risk for severe allergic reactions and, in addition, indicate broad cross-reactivity to TM from other shellfish species and perhaps insects and mites.

Testing IgE to more than one TM is probably providing more information about cross-reactivity between crustaceans and mollusks. Similar assumptions are related to the other described shellfish allergens see above , i. Increasing test sensitivity through the use of single molecules might be useful in less stable allergens i. Increased analytical specificity can assist uncovering associated risks, i.

However, none of these candidates might serve as a single marker for species-specific sensitization due to variable degrees of IgE-related cross-reactivity, which still needs to be addressed. Recent advances in PCR based allergen-specific IgE quantification have further improved the sensitivity and specificity to single allergens, using serum from a finger-prick, which is of particular advantage for infant allergy testing [ 39 ]. In conclusion, no species-specific allergens have been identified so far, making it difficult to precisely diagnose allergy to a specific crustacean or mollusk species with the use of allergen molecules [ 3 , 40 ].

If more of the already identified and additional allergens are available for diagnostics, it might be helpful to test one per protein family, ensuring maximum test sensitivity and enhanced molecular specificity, particularly if TM is not the major allergen. This does, however, not solve the question of potential clinical cross-reactions to closely related shellfish species: only anamnestic data or oral challenges can indicate or rule out clinically relevant allergic reactions to certain shellfish species.

Serum based IgE quantification tests are available for a wide variety of crustacean and mollusk species as well as for cross-reactive invertebrate species such as dust-mites and cockroaches. IgE quantification tests for single component allergens are currently only available for shrimp tropomyosin rPen a 1. However, some additional shellfish allergens are available in multiplex microarray format for prawn tropomyosin nPen m 1 , arginine kinase nPen m 2 , and sarcoplasmic calcium binding protein rPen m 4.

It has been suggested that IgE reactivity to tropomyosin is a better predictor of shrimp allergy as compared to skin prick testing SPT or IgE to whole shrimp extract [ 19 , 23 ]. However, also sarcoplasmic calcium-binding protein Pen m 4 reactivity has been associated with clinical reactivity to shrimp. The combination of reactivity to both allergens might increase the sensitivity to detect clinically allergic patients, but has still to be confirmed.

The consumption of seafood is very different from most other food allergen sources. It can trigger clinical adverse symptoms, although non-allergic in origin, being similar in clinical presentation to true IgE-mediated allergic reactions. These substances are found in seafood much more frequently as compared to any other food source.

An atypical clinical history or an inconsistent history always suggests a non-atopic etiology, such as contamination with marine bio-toxins, parasites, bacteria, and viruses [ 41 , 42 ]. Because of the similarity in clinical reactions of affected individuals, it is essential to differentiate adverse reactions from true shellfish allergy and understand the molecular nature of the offending allergens for improved component-resolved diagnosis.

Food challenge or double blind placebo controlled food challenge DBPCFC can be performed to confirm clinical reactivity to crustacean and mollusk species. However, such provocation tests are not performed routinely because of increased risk and costs, and are only performed for investigating individual cases. Most of the clinical studies on cross-reactivity have been conducted using tropomyosin as the major pan-allergen.

However, other shellfish allergens may play a role in immunological cross-sensitization. A recent study has shown that allergens other than tropomyosin, such as arginine kinase, might also be responsible for cross-reactivity between shellfish and inhalant invertebrate allergen sources [ 27 , 43 ]. In addition, hemocyanin has been demonstrated to be cross-reactive and is also a known cockroach allergen [ 44 , 45 ].

However, an in-depth investigation into the conservation or relevance of specific IgE epitopes between pan-allergens from crustaceans and mollusks and clinical cross-reactivity to mites and cockroaches has not been conducted or confirmed using a larger number of shellfish allergic patients.

In case of severe allergic reaction, allergen-specific IgE should precede any in vivo tests, i. IgE diagnostics should include. If extract- and TM-specific IgE results are positive with quantitative IgE-levels being higher to TM than to the whole extract, immunodominant sensitization to shellfish TM is likely, and broad serological cross-reactivity to other shellfish species is to be expected. During interpretation of the test, concordance between recorded symptoms and the identified shellfish species should be checked.

Only in case of corresponding symptoms and a positive sensitization test, clinically relevant allergy has successfully been demonstrated. If only the extract-specific IgE, but not the TM-specific IgE is positive, sensitization to TM is unlikely, but other shellfish allergens might be involved.

If both IgE-tests shellfish extract- and TM-specific IgE turn out to be negative, it is mandatory to perform a skin test, i. Many people falsely believe that iodine may trigger an allergic reaction in people with a shellfish allergy.

Iodine is often used in medications and in contrast agents used in medical imaging. The misconception is largely related to a Florida court case about a man who died from a severe allergic reaction. The man had a known shellfish allergy. The allergic reaction occurred a few minutes after he received contrast iodine from a cardiologist. A study published in the Journal of Emergency Medicine concluded that iodine is not an allergen. A simple skin prick test can identify a shellfish allergy.

The test involves puncturing the skin of the forearm and introducing a small amount of the allergen into it. Allergy testing is the only sure way to tell if a reaction after eating shellfish is indeed a shellfish allergy. The only way to prevent a shellfish allergy is to avoid all shellfish and all products that contain shellfish.

Ask the staff how food is prepared when eating in a restaurant. Asian restaurants often serve dishes that contain fish sauce as a flavoring base. A shellfish-based broth or sauce may trigger an allergic reaction. Stay away from steam tables or buffets. Avoid eating at a seafood restaurant or shopping in a fish market. Some people react even if they inhale steam or vapor from cooking shellfish.

Cross-contamination also is possible in establishments that serve seafood. Read food labels carefully. Companies are required to disclose whether their food product contains shellfish. Let people know. When flying, contact the airline in advance to find out whether any fish or shellfish dishes will be prepared and served on the flight.