Fish allergy
Fish allergy is an immune hypersensitivity to proteins found in fish. Symptoms can be either rapid or gradual in onset. The latter can take hours to days to appear. The former may include anaphylaxis, a potentially life-threatening condition which requires treatment with epinephrine. Other presentations may include atopic dermatitis or inflammation of the esophagus. Fish is one of the eight common food allergens, responsible for 90% of allergic reactions to foods: cow's milk, eggs, wheat, shellfish, peanuts, tree nuts, fish, and soy beans.
Unlike early childhood allergic reactions to milk and eggs, which often lessen as the children age, fish allergy tends to first appear in school-age children and persist in adulthood. Strong predictors for adult-persistence are anaphylaxis, high fish-specific serum immunoglobulin E and robust response to the skin prick test. It is unclear if the early introduction of fish to the diet of babies aged 4–6 months decreases the risk of later development of fish allergy. Adult onset of fish allergy is common in workers in the fish catching and processing industry.
Signs and symptoms
Food allergies in general usually have a fast onset. Symptoms may include: rash, hives, itching of mouth, lips, tongue, throat, eyes, skin, or other areas, swelling of lips, tongue, eyelids, or the whole face, difficulty swallowing, runny or congested nose, hoarse voice, wheezing, shortness of breath, diarrhea, abdominal pain, lightheadedness, fainting, nausea, or vomiting. Symptoms of allergies vary from person to person and may vary from incident to incident. Serious danger regarding allergies can begin when the respiratory tract or blood circulation is affected. The former can be indicated by wheezing, a blocked airway and cyanosis, the latter by weak pulse, pale skin, and fainting. When these symptoms occur the allergic reaction is called anaphylaxis. Anaphylaxis occurs when IgE antibodies are involved, and areas of the body that are not in direct contact with the food become affected and show severe symptoms. Untreated, this can proceed to vasodilation, a low blood pressure situation called anaphylactic shock, and death.Causes
Eating fish
The cause is typically the eating of fish or foods that contain fish. Once an allergic reaction has occurred it usually remains a lifelong sensitivity. Briefly, the immune system overreacts to proteins found in fish. The allergic reaction to shellfish and crustaceans such as lobster and shrimp is to a different protein - tropomyosin - so there is no cross-reactivity between fish and shellfish allergy.'Hidden' allergen - a fish parasite
The food-borne parasite Anisakis is a genus of nematodes known to infect fish. Anisakis are directly infective to humans when infected fish is consumed raw or slightly processed, as for cerviche, causing a condition call anisakiasis, and in addition, can cause an allergic reaction to nematode proteins, even if the infected fish has been frozen or cooked. Allergic reactions can include hives, asthma and true anaphylactic reactions.Occupational exposure
An industry review conducted in 1990 estimated that 28.5 million people worldwide were engaged in some aspect of the seafood industry: fishing, aquaculture, processing and industrial cooking. Men predominate in fishing, women in processing facilities. Exposure to fish allergenic proteins includes inhalation of wet aerosols from fresh fish handling, inhalation of dry aerosols from fishmeal processing, and dermal contact through skin breaks and cuts. Prevalence of seafood-induced adult asthma is on the order of 10%. Prevalence of skin allergy reactions, often characterized by itchy rash, range from 3% to 11%. The fish-induced health outcomes are mainly due to the protein parvalbumin causing an IgE mediated immune system response.Exercise as a contributing factor
There is a condition called food-dependent, exercise-induced anaphylaxis. Exercise can trigger hives and more severe symptoms of an allergic reaction. For some people with this condition, exercise alone is not sufficient, nor consumption of a food to which they are mildly allergic sufficient, but when the food in question is consumed within a few hours before high intensity exercise, the result can be anaphylaxis. Fish are specifically mentioned as a causative food. One theory is that exercise is stimulating the release of mediators such as histamine from IgE-activated mast cells. Two of the reviews postulate that exercise is not essential for the development of symptoms, but rather that it is one of several augmentation factors, citing evidence that the culprit food in combination with alcohol or aspirin will result in a respiratory anaphylactic reaction.Mechanisms
Allergic response
Conditions caused by food allergies are classified into three groups according to the mechanism of the allergic response:- IgE-mediated – the most common type, manifesting acute changes that occur shortly after eating, and may progress to anaphylaxis
- Non-IgE mediated – characterized by an immune response not involving immunoglobulin E; may occur hours to days after eating, complicating diagnosis
- IgE and non-IgE-mediated – a hybrid of the above two types
In the early stages of acute allergic reaction, lymphocytes previously sensitized to a specific protein or protein fraction react by quickly producing a particular type of antibody known as secreted IgE, which circulates in the blood and binds to IgE-specific receptors on the surface of other kinds of immune cells called mast cells and basophils. Both of these are involved in the acute inflammatory response. Activated mast cells and basophils undergo a process called degranulation, during which they release histamine and other inflammatory chemical mediators called into the surrounding tissue causing several systemic effects, such as vasodilation, mucous secretion, nerve stimulation, and smooth-muscle contraction. This results in runny nose, itchiness, shortness of breath, and potentially anaphylaxis. Depending on the individual, the allergen, and the mode of introduction, the symptoms can be system-wide, or localized to particular body systems; asthma is localized to the respiratory system while eczema is localized to the skin.
After the chemical mediators of the acute response subside, late-phase responses can often occur due to the migration of other white blood cells such as neutrophils, lymphocytes, eosinophils, and macrophages to the initial reaction sites. This is usually seen 2–24 hours after the original reaction. Cytokines from mast cells may also play a role in the persistence of long-term effects. Late-phase responses seen in asthma are slightly different from those seen in other allergic responses, although they are still caused by release of mediators from eosinophils.
In addition to IgE-mediated responses, fish allergy can manifest as atopic dermatitis, especially in infants and young children. Some will display both, so that a child could react to an oral food challenge with allergic symptoms, followed a day or two later with a flare up of atopic dermatitis and/or gastrointestinal symptoms, including allergic eosinophilic esophagitis.
Fish allergenic proteins
The protein parvalbumin has been identified as the major allergen causing fish allergy. Parvalbumin is resistant to heat and enzymatic digestion, so cooking does not diminish its allergenic potency, nor do digestive enzymes. Bony fishes manifest β-parvalbumin whereas cartilaginous fishes such as sharks and rays manifest α-parvalbumin; allergenicity to bony fishes has a low cross-reactivity to cartilaginous fishes. In addition to β-parvalbumin, fish enolase, aldolase and collagen can also trigger allergic reactions. Fish collagen is widely used in the food industry in foods such as gummy candies, jelly beans or marshmallows. It may also be marketed as a dietary supplement ingredient or as an inactive ingredient in pharmaceutical products. Standardized skin tests that incorporate parvalbumin for fish sensitivity will miss collagen allergy. People may be allergic to parvalbumin, collagen, or both.Non-allergic intolerance
There is a reaction from consuming fish that mimics an allergic reaction. Scombroid is a foodborne illness that results from high in histamine due to inappropriate storage or processing. Histamine is the main natural chemical responsible for true allergic reactions, hence the confusion with fish allergy. Scombroid symptom onset is typically 10-30 minutes after consumption, and may include flushed skin, headache, itchiness, blurred vision, abdominal cramps and diarrhea. Fish commonly implicated include tuna, mackerel, sardine, anchovy, herring, bluefish, amberjack and marlin. These fish naturally have high levels of the amino acid histidine, which is converted to histamine when bacterial growth occurs during improper storage. Subsequent cooking, smoking, canning or freezing does not eliminate the histamine.Diagnosis
Diagnosis of fish allergy is based on the person's history of allergic reactions, skin prick test and measurement of fish-specific serum immunoglobulin E. Confirmation is by double-blind, placebo-controlled food challenges. Self-reported fish allergy often fails to be confirmed by food challenge.Prevention
When fish is introduced to a baby's diet is thought to affect risk of developing allergy, but there are contradictory recommendations. Reviews of allergens in general stated that introducing solid foods at 4–6 months may result in the lowest subsequent allergy risk. Reviews specific to when fish is introduced to the diet state that fish consumption during the first year of life reduce the subsequent risks of eczema and allergic rhinitis, but maternal consumption during pregnancy had no such effect.Treatment
Treatment for accidental ingestion of fish products by allergic individuals varies depending on the sensitivity of the person. An antihistamine such as diphenhydramine may be prescribed. Sometimes prednisone will be prescribed to prevent a possible late phase Type I hypersensitivity reaction. Severe allergic reactions may require treatment with an epinephrine pen, i.e., an injection device designed to be used by a non-healthcare professional when emergency treatment is warranted. Unlike for egg allergy, for which there is active research on trying oral immunotherapy to desensitize people to egg allergens, a 2015 review mentioned that there are no published clinical trials evaluating oral immunotherapy for fish allergy.Prognosis
Unlike milk and egg allergies, fish allergy usually persists into adulthood.Epidemiology
Incidence and prevalence are terms commonly used in describing disease epidemiology. Incidence is newly diagnosed cases, which can be expressed as new cases per year per million people. Prevalence is the number of cases alive, expressible as existing cases per million people during a period of time. Strong predictors for adult-persistent allergy are anaphylactic symptoms as a child, high fish-specific serum IgE and robust response to the skin prick test. Reviews cite self-reported fish allergy in range of 0 to 2.5% in the general population. Self-reported allergy prevalence is always higher than food-challenge confirmed allergy, which two reviews put at 0.1% and 0.3%, respectively.Society and culture
Whether food allergy prevalence is increasing or not, food allergy awareness has definitely increased, with impacts on the quality of life for children, their parents and their immediate caregivers. In the United States, the Food Allergen Labeling and Consumer Protection Act of 2004 causes people to be reminded of allergy problems every time they handle a food package, and restaurants have added allergen warnings to menus. The Culinary Institute of America, a premier school for chef training, has courses in allergen-free cooking and a separate teaching kitchen. School systems have protocols about what foods can be brought into the school. Despite all these precautions, people with serious allergies are aware that accidental exposure can easily occur at other peoples' houses, at school or in restaurants. Food fear has a significant impact on quality of life.Regulation of labelling
In response to the risk that certain foods pose to those with food allergies, some countries have responded by instituting labeling laws that require food products to clearly inform consumers if their products contain major allergens or byproducts of major allergens among the ingredients intentionally added to foods. Nevertheless, there are no labeling laws to mandatory declare the presence of trace amounts in the final product as a consequence of cross-contamination.Ingredients intentionally added
In the United States, the Food Allergen Labeling and Consumer Protection Act of 2004 requires companies to disclose on the label whether a packaged food product contains any of these eight major food allergens, added intentionally: cow's milk, peanuts, eggs, shellfish, fish, tree nuts, soy and wheat. This list originated in 1999 from the World Health Organisation Codex Alimentarius Commission. To meet FALCPA labeling requirements, if an ingredient is derived from one of the required-label allergens, then it must either have its "food sourced name" in parentheses, for example "Casein," or as an alternative, there must be a statement separate but adjacent to the ingredients list: "Contains milk". The European Union requires listing for those eight major allergens plus molluscs, celery, mustard, lupin, sesame and sulfites.FALCPA applies to packaged foods regulated by the FDA, which does not include poultry, most meats, certain egg products, and most alcoholic beverages. However, some meat, poultry, and egg processed products may contain allergenic ingredients. These products are regulated by the Food Safety and Inspection Service, which requires that any ingredient be declared in the labeling only by its common or usual name. Neither the identification of the source of a specific ingredient in a parenthetical statement nor the use of statements to alert for the presence of specific ingredients, like "Contains: milk", are mandatory according to FSIS. FALCPA also does not apply to food prepared in restaurants. The EU Food Information for Consumers Regulation 1169/2011 – requires food businesses to provide allergy information on food sold unpackaged, for example, in catering outlets, deli counters, bakeries and sandwich bars.