Allergy to fish – sources, symptoms and treatments

Fish are a healthy product, however, like some vegetables and fruits, they can cause allergies. An allergic reaction is caused in children and adults by parvalbumin – a protein found in fish. Fish allergy is the most common in countries where fish is a basic element of regional cuisine. Fish allergy occurs in about 2% of the population. 

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The main symptoms of fish allergies include gastrointestinal problems, asthma, urticaria and Quincke’s edema. In some cases, anaphylactic reaction may occur. Symptoms of fish allergies may occur a few minutes after eating fish, or only after about 24-48 hours. Employees of fish processing plants, because of their constant exposure to fish dust and fumes, are at risk of catching fish allergies. Allergy to fish is most often caused by parvalbumin (around 95%). Due to the similar amino acid sequence in parvalbumin in various fish species, the allergy can be sensitized to many species of fish. 

Causes of allergies to fish 

Allergy can be caused by both freshwater and marine fish. The most sensitizing fish include cod, herring, sprat, eel, carp, perch. People who are allergic react to both fried and boiled fish. Heat treatment, even the most advanced in terms of the processing temperature achieved, such as frying, grilling or baking do not cause the breakdown of parvalbumin. Parvalbumin is found in white muscle tissue. Therefore, the least sensitizing fish are dark meat, including fish saw, salmon and tuna. 

Symptoms of fish allergies 

Symptoms of fish allergies can be associated with skin changes such as redness and urticaria. Occasionally swelling of the face or lips appears. On the day after the day of consumption of fish, the atopic dermatitis may become more severe 

. Gastrointestinal symptoms accompanying allergies to fish include vomiting and nausea and diarrhea. Gastric complaints can have a very sharp course and show a strong diarrhea with an admixture of blood. The syndrome of these symptoms is referred to as intestinal inflammation due to food-derived proteins (FPIES). Both asthma, wheezing, breathing problems, cough and rhinitis in the course of fish allergy appear relatively rarely compared to other symptoms. Dyspnoea more often testify to Quince’s edema. 

Undesirable reactions to fish are not always the result of allergies to fish. The reaction may be a pseudo allergy – then the immune system does not take part in the reaction. Some fish species contain a lot of histamine can also trigger the release of histamine in the body, which manifests, for example, urticaria, intestinal cramps, or swelling. Pseudo allergic reactions may also be caused by the presence of heavy metals or a bacterial infection resulting from too long or improper fish storage and. When eating fish, one should also be aware of the allergy to the parasite from the cluster of nematodes – Anisakis simplex. 

Symptoms of allergy in children 

In the youngest patients, a fish allergy can be manifested by vomiting, intense rehydration, diarrhea, colic and abdominal distension. Impaired nutritional status associated with allergy is manifested by slowing down the rate of growth and inhibition of weight gain. Symptoms of respiratory allergies include sapka, runny nose, difficulty in breathing and wheezing in the chest. Fish allergy can also cause atopic dermatitis (so-called protein blemish), swelling of the lips and urticaria. Children are like adults who are exposed to anaphylactic shock. 

Dangerous anaphylactic shock 

In people with severe allergies, the intake of fish can lead to a dangerous symptom – anaphylactic reaction. After just a few minutes from eating fish food, the allergic person may develop dyspnoea, circulatory problems, loss of consciousness, collapse and apnea. In the event of anaphylactic shock symptoms, an ambulance should be called immediately. 

Diagnosis of fish allergies 

Fish allergy can develop at every stage of life. Food allergy of childhood to fish disappears with age in few children and adolescents. An allergic reaction often arises in adolescents who for years have eaten fish and have not been accompanied by any symptoms. In 40% of cases, fish allergy becomes active only in adulthood. The diagnosis can be confirmed by various diagnostic methods, such as the prick skin test and the study of specific IgE antibodies in blood serum. If, after the above tests, there are still doubts about the allergy to the fish, a provocative test is carried out. If after the oral challenge test the result is positive, the patient is given an elimination diet. A negative result of an oral provocation test suggests that additional tests be performed on the content of toxins and parasites. 

Treatment of fish allergies 

The basic method of treatment of fish allergies is to avoid consuming fish species, on which allergy has been confirmed by research. Even the fumes created during fish cooking may show allergy symptoms. Cutlery that has been in contact with fish may also cause allergy symptoms. Accidental contamination of fish with other products is declared by producers – the packaging is placed on the label (it may contain traces of fish). 

In the event of allergic symptoms to the fish, you can use antiallergics. The allergy should have a first aid kit prescribed by a doctor. Sick people should inform people in their immediate environment about their allergies and possible symptoms. Avoid fish products and products that could contain fish and fish products, surimi and dietary supplements (omega-3 acids derived from fish) containing fish oil. For people who are highly sensitized, it is recommended to completely opt out of visiting the restaurant. 

Unfortunately, the attempts of immunotherapy with regard to fish allergies taken in the past have not brought the intended results. They were also not safe enough. Since 2009, studies have been underway to develop a vaccine for subcutaneous immunotherapy in fish allergy under the direction of Ronald van Ree as part of the Food Allergy Specific Immunotherapy project. The project also involves the Department of Immunology, Rheumatology and Allergy Medical University of Lodz, which in 2015 began to study the effectiveness and safety of the developed vaccine (A. Drewnik, ML Kowalski, Allergy to fish, in Allergy Asthma Immunology 2016, 21, pp. 88-95). 

Reducing the risk of allergy 

In order to reduce the risk of allergies in children, the child can be exclusively breastfed for the first six months of life, and for the following months continue breastfeeding combined with the introduction of complementary foods. Children belonging to the group of increased risk of allergy (occurrence of allergic disease in parents or siblings) should be fed in the first half-year of life with breast milk and protein hydrolysates – special mixtures that reduce the risk of allergy. 

There is no scientific evidence that delayed introduction of potentially allergenic foods – fish and seafood – reduces the risk of allergy. Similarly, the elimination diet during pregnancy also does not reduce the risk of allergy in the child, and may lead to nutritional deficiencies in the mother, so it is even a threat to the health of the child. There is also no evidence that the elimination diet during lactation prevents the occurrence of allergies in the child. 

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You can read also: Krill oil vs fish oil: which is better for you?

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