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Shrimps and other crustaceans Allergy

Crustaceans are among the most commonly consumed seafoods. Crustaceans belong to the Arthropod family. Crustaceans are divided into six major subgroups that include 44,000 species. Amongst these is a variety of commonly and less commonly eaten sea foods like langoustine, lobster, crayfish, and crab. Other sea foods like clams, mussels, oysters, scallops, abalone and squid are no crustaceans but molluscs or shell fish. Crustacean allergy is a so-called IgE-mediated food allergy. IgE (Immunoglobulin E) is the allergy antibody.

Symptoms

Reactions range from mild oral allergy syndrome (itching of the lips, mouth, or throat, and swelling of the lips, tongue, throat, and palate) to life-threatening systemic anaphylaxis (difficulty breathing, drop in blood pressure, and even death). Symptoms occur within one to one hour of ingestion (90% of cases). However, urticaria (hives) is the most frequent symptom. Others symptoms affecting the skin (itching, swelling), gastro-intestinal tract (nausea, cramping heartburn, and diarrhoea), respiratory symptoms (asthma, hayfever), and eyes (conjunctivitis) have been reported. Shellfish are frequently implicated in fatal anaphylactic reactions and are the third most important cause of anaphylaxis after peanuts and tree nuts (cashews, almonds, pecans, walnuts, etc.).

Symptoms most often occur when the seafood is ingested (generally require higher doses to elicit a reaction), but can also appear when raw seafood is handled and even after inhaling steam while crustaceans such as shrimp are being cooked (may cause respiratory reactions). Cooking oil contaminated with seafood residues has also been reported to cause adverse reactions. Allergic reactions in workers at every stage of seafood processing also occur and are a serious public health problem in countries with major shellfish industries.

Related foods (cross-reactions)

It has been estimated that 75% of individuals who are allergic to one type of crustacean (shrimp, lobster, crawfish, or crab) are also allergic to another type. This is referred to as cross-reactivity. Cross-reactions between crustaceans and molluscs (oysters, squid, scallops) are also possible involving the same type of proteins in these foods. In fact, the molecules responsible for the cross-reactions can also cause cross-reactions between crustaceans, dust mites, cockroaches, and chironomid (used as fish food). However, no cross-reactions have been reported between crustaceans and fish such as Pollock, salmon, tuna, mackerel, trout, and anchovies.

Who, when, how long and how often?

Food allergies are most frequent in children, but adults are not exempt. Crustaceans, peanuts, fish, and tree nuts are the most common causes of food allergies among adults. Fish and shellfish allergies are estimated to affect approximately 1% of the general population. Countries where large amounts of crustaceans are consumed, such as the Scandinavian countries, have higher rates of crustacean allergies, although no species-specific studies have been conducted. Little is known about their persistence, but all evidence indicates that crustacean allergies are usually not outgrown.

How much is too much?

Symptoms most often occur when the seafood is ingested (generally require higher doses to elicit a reaction), but can also appear when raw seafood is handled and even after inhaling steam while crustaceans such as shrimp are being cooked (may cause respiratory reactions). Cooking oil contaminated with seafood residues has also been reported to cause adverse reactions. Allergic reactions in workers at every stage of seafood processing also occur and are a serious public health problem in countries with major shellfish industries.

While one shrimp is often enough to induce an allergic reaction, some people react to even smaller amounts. Lowest threshold dosages remain to be elucidated.

Diagnosis

A detailed patient history is first taken. Skin and laboratory tests are then used to help eliminate allergic foods from the diet. In the case of crustaceans, a positive skin test combined with elevated antibody levels allow shrimp allergies, for example, to be diagnosed with 87% certainty. There is no established threshold value for crustacean specific IgE.

However, food challenges (giving increasing amounts of potentially allergic food in graduated steps to patients to determine whether they will have an allergic reaction) are the most effective way of determining whether a person is truly allergic to a certain food. Initial food challenges are always conducted as double-blind, placebo controlled tests. In the case of crustaceans, for example, food challenges involve double-blind, placebo-controlled tests using increasing doses of the boiled crustacean in vanilla ice cream containing grape flavouring. If the double-blind placebo-controlled food challenge is negative, an open food challenge is generally performed. Food challenges should only be performed in a hospital setting with highly trained personnel used to dealing with anaphylactic reactions. Patients with a recent history of severe reactions should not be challenged. In addition, patients that are allergic to one type of crustacean should be tested for allergies reactions to all the other crustaceans because of the potential for cross-reactions.

Where do I find crustacean?

Crustaceans or crustacean residues may be present in certain processed foods. It is thus very important that people with allergies to crustaceans develop the habit of carefully reading ingredient labels and be aware of the words, terms, and indicators used on labels that indicate the presence of crustaceans or crustacean residues. Food products can contain hidden allergens.

Non-food products

Crustaceans are used in few non-food products such as creams. Contact with these products can induce allergic reactions.

Avoidance

For patients diagnosed with a crustacean allergy, avoidance of crustaceans is the only proven therapy, especially since adverse reactions to very small amounts of crustaceans are not uncommon. It is thus very important that people with allergies to crustaceans develop the habit of carefully reading ingredient labels and that they are aware of words, terms, and indicators used on labels that indicate the presence of crustaceans or crustacean residues. Food products can contain hidden allergens. Eating out especially in restaurants with South-East Asian cuisine is a risk factor for unexpected contact with crustaceans. Annex IIIa of the new EU labelling directive makes the listing of crustaceans and crustacean products on labels mandatory.