The major allergen responsible for fish allergy is a protein called parvalbumin, which controls the balance of calcium in the white meat of fish. Seafood is an important part of the human diet, while a healthy source of protein, fish also can cause illness in humans through allergic and non- allergic food reactions. Seafood allergy is a type of food allergy.
It is a hypersensitivity to dietary substances from shellfish, scaly fish, or crustaceans, causing an overreaction of the immune system, which may lead to severe physical symptoms.
Finned fish can cause severe allergic reactions. This allergy is usually life-long. The protein in the flesh of most fish commonly causes the allergic reaction, however, it is possible to have a reaction to fish gelatin, made from the skin and bone of fish.
Definitions
Allergy: Term for a foreign substance which induces an allergic or hypersensitivity response through the production of immunoglobulin E. Sensitization: the production of a specific type of allergic antibody by the immune system resulting in a positive allergy test, such as to a particular food or pollen.
It is possible for a person to make a specific allergic antibody to a food, for example, without experiencing allergic reactions when that food is eaten. Parvalbumin: a calcium- binding albumin protein with low molecular weight (typically 9-11 kDa)
Cause of Fish Allergy
The major allergen responsible for fish allergy is a protein called parvalbumin, which controls the balance of calcium in the white meat of fish.
Parvalbumin is localized in fast- contracting muscles, where its levels are highest, and in the brain and some endocrine tissues.
Parvalbumins are very similar between different species of fish so if a person is allergic to one species of fish, it is very common to be allergic to other fish species as well.
Gelatin is another major allergen that is shared among species of fish. When a person who is sensitized to fish comes into contact with or eats fish, an allergic reaction occurs, leading to the symptoms of allergy.
Symptoms of Fish Allergy
The symptoms of fish allergy are similar to those of other food allergies. Almost all people with fish allergy will experience symptoms within an hour of eating the food.
The most common symptoms include generalized itching, hives and swelling, vomiting, and respiratory symptoms such as wheezing and chest tightness – although fatal anaphylaxis can also occur.
Some people with fish allergy experience hives and itching when they touch raw fish, but are able to eat cooked fish meat without having allergic symptoms. Proteins released into steam when fish is being cooked can also cause allergic symptoms of asthma and hay fever in people with an allergy to fish.
Avoidance of Fish
Most people with an allergy to one type of fish should avoid eating any species of fish, given that the major fish allergens are shared among many species of fish.
It also seems a good idea for people with fish allergy to avoid seafood restaurants, given the chance of contamination of other foods with fish allergen.
Fish proteins may also be present in steam released from cooking fish, which may trigger allergic reactions in people with fish allergy.
Fish proteins can also be hidden in certain foods, and therefore cause unexpected allergic reactions in people with fish allergy.
Avoidance of other fish products, such as sushi, caviar, roe, fish oil capsules and cod liver oil would seem prudent in people with fish allergy.
Shellfish are not related to fish, and therefore could be eaten by people with fish allergy.
However, the danger of cross-contamination between fish and shellfish exists meaning that a person with a fish allergy would not want to eat shellfish in a seafood restaurant, since the food could be contaminated with fish.
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Diagnosis and Treatment of Fish Allergy
The diagnosis of fish allergy can be made when a person has experienced allergic symptoms after eating fish, and has as a positive allergy test to fish, either with a skin test or a blood test.
Skin testing remains the best way to confirm the diagnosis of fish allergy, although blood testing has the advantage of measuring the amount of allergic antibody against fish.
The level of allergic antibody to fish can be helpful in determining whether a person actually has a true fish allergy, has possibly outgrown the fish allergy, or may simply be sensitized to fish, but without experiencing allergic symptoms with eating fish.
A form of food poisoning, called scombroid, involves eating spoiled fish containing large amounts of histamine. Scombroid poisoning usually occurs in large dark meat fish such as tuna and mackerel.
Since this poison develops after a fish is caught and dies, where the fish is caught doesn’t really matter. The main factor is how long the fish sits out before being refrigerated or frozen.
The harmful substances that cause Ciguatera, Scombroid, and shellfish poisoning are heat stable, so no amount of cooking will protect you from becoming poisoned if you eat fish that is contaminated.
Symptoms depend on the specific type of poisoning. The symptoms of scombroidosis are virtually identical to symptoms of true food allergy, although allergy testing is negative, since no allergic antibody is present.
Scombroid poisoning symptoms usually occur immediately after eating the fish. They may include:
Breathing problems (in severe cases), extremely red skin on face and body, flushing, hives and itching, nausea and vomiting.
If you have scombroid poisoning, you may receive:
An antihistamine medication, such as diphenhydramine (Benadryl) Fluids by IV (to replace fluids lost from vomiting and diarrhea) Medicines to stop vomiting
Medicines to treat severe allergic reactions (if needed) Breathing tube (in rare cases)
The treatment of fish allergy mainly involves the avoidance of fish. If a fish-allergic person eats fish, and experiences an allergic reaction, immediate treatment is required.
This often involves the use of injectable epinephrine, such as with an Epi-Pen or Twin-Ject device, although mild reactions may be treated with oral antihistamines.
People with fish allergy should wear a Medic-Alert bracelet listing their food allergy information, and should carry injectable epinephrine at all times given the possibility of the accidental ingestion of fish proteins.
Other treatment include:
Avoid foods containing the allergen, adrenaline injection if anaphylactic reaction occurs, antihistamines, bronchodilators for asthmatic symptoms.
The central concept of management of food allergy is allergen avoidance. When this is not possible or inadvertent allergen exposure occurs, treatment depends on the nature and severity of the reaction.
Treatments include:
Dietary modification and allergen avoidance – with education of children and parents.
No treatment – if symptoms are mild and self-limiting.
Antihistamines – Useful for allergic rhinitis and some allergy mediated skin conditions. Not helpful in asthma except for mild seasonal asthma where allergy may be a precipitant.
In summary, fish allergy is not an emergency but Shellfish poisoning may be a medical emergency. With sudden or significant symptoms, the person should be taken immediately to hospital.
Seafood allergies are usually treated with an exclusion diet and vigilant avoidance of foods that may be contaminated with shellfish or fish ingredients and/or oils.
The most severe seafood allergy reaction is called anaphylaxis, which is an emergency, requiring immediate attention. It is treated with Epinephrine, which can be administered with an Epi-Pen.
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