What Is Fish Allergy

Introduction:

Fish is one of the eight common food allergens that are responsible for 90% of allergic reactions to foods. Fish allergy is characterised by immune hypersensitivity when a person eats or touches the fish. The immune system recognizes it as a threat and releases chemicals like histamine in response to it, leading to allergic reactions.¹

Prevalence:

Fish allergies are most common in areas like Scandinavia and some Asian regions where fish is a local diet. It affects only 1% of the total population but is more common in children than adults¹.

Different types of fish allergies:

There are two main types of fish allergies: IgE-mediated fish allergy and non-IgE-mediated fish allergy.¹

1. IgE-mediated fish allergy:
   This is the classic type of fish allergy that involves the production of immunoglobulin E (IgE) antibodies by your immune system. These antibodies bind to allergens and activate mast cells and basophils, which release histamine and other chemicals that cause inflammation and symptoms. IgE-mediated fish allergy can occur within minutes or hours after exposure to fish and can cause anaphylaxis.
2. Non-IgE-mediated fish allergy: This is a less common type of fish allergy that does not involve IgE antibodies but other immune responses. Non-IgE mediated fish allergy can cause delayed or chronic symptoms that appear hours or days after exposure to fish. These symptoms include gastrointestinal disorders such as eosinophilic, esophagitis or enterocolitis, skin disorders such as atopic dermatitis or contact dermatitis, or respiratory disorders such as asthma or rhinitis.

Fish species that trigger allergies:

There are more than 20,000 species of fish in the world, but only a few of them are commonly consumed by humans.²
Some of the most popular ones are: 

• Tuna
• Salmon
• Cod
• Herring
• Trout
• Mackerel
• Halibut
• Tilapia
• Catfish

However, not all fish are equally allergenic. Some of them may contain more allergens than others, and some of them share similar allergens with other species. This means that if you are allergic to one type of fish, you may also be allergic to other fish.

Fish allergens:

Fish allergens are the substances that are responsible for causing fish allergies. There are different types of fish allergens, the most common of which is parvalbumin.³
Some of the common fish allergens are discussed below:

Parvalbumin

Parvalbumin is the most abundant protein in fish, binding to calcium and magnesium ions and helping regulate muscle contraction. They are found in the muscle tissue of most fish species, especially cold-water fish such as salmon, cod, herring, and trout.

Parvalbumin is highly resistant to heat, thus causing allergic reactions even after cooking or processing. It is also very similar among different fish species, which means if you are allergic to one fish, you’re likely to be allergic to other fish as well. This is called cross-reactivity.³

Collagen

This is an important fish allergen. It is a protein that provides strength to the skin, bones, cartilage, and tendons of animals. Collagen is found in the skin and bones of fish, as well as in some processed fish products like gelatin, stock, and surimi. Some people are allergic to a modified form of type 1 collagen, fish gelatin, which can cause high IgE cross-reactivity. Type I collagen obtained from the meat and skin of various fish species was found to bind IgE in 20% of fish-allergic patients and trigger the activation of basophils that had been sensitised with patients' sera.^1,3

β-enolase

Enolase is an enzyme involved in the glycolysis pathway, which is essential for energy production in cells. -enolase specifically catalyses the conversion of 2-phosphoglycerate to phosphoenolpyruvate. In vertebrates, enolase exists in three tissue-specific isoforms: α, β, and γ. Surprisingly, fish-enolases, despite sharing significant sequence similarity with their human counterparts, have been identified as allergens in several fish species, including cod (Gad m 2), salmon (Sal s 2), and even chicken meat (Gal d 9). The allergenicity of fish enolases can vary among individuals, and the cross-reactivity between enolases from different fish species can be highly variable. This variability may be due to less conserved regions on the molecular surface.^1,3

Aldolase A

Aldolase is another enzyme involved in glycolysis, responsible for breaking down fructose-1,6-bisphosphate into dihydroxyacetone phosphate and glyceraldehyde 3-phosphate. There are three forms of class I aldolase: aldolase A, B, and C. Aldolase A is preferentially expressed in muscle and brain tissue. Like -enolase, aldolases from fish, including cod (Gad m 3), salmon (Sal s 3), and tuna (Thu a 3), have been identified as minor allergens. However, the degree of IgE cross-reactivity among these allergens can vary among fish-allergic individuals.³

Tropomyosin

Tropomyosins are proteins that play a crucial role in regulating muscle contractions by interacting with actin filaments. Invertebrate tropomyosins are known to be major food allergens in crustaceans and molluscs. While vertebrate tropomyosins have lower allergenicity due to their similarity to human tropomyosins, some fish tropomyosins, such as Ore m4 from tilapia, have been identified as allergens. There is potential cross-reactivity with tropomyosins from crustaceans.³

Creatine kinase

Creatine kinase (CK) is an enzyme involved in cellular energy metabolism, converting creatine to phosphocreatine. CK has been identified as a minor allergen in some fish species, including catfish (Pan h 7) and salmon (Sal s 7). However, its allergenicity is relatively low compared to other fish allergens.³

Vitellogenin

Vitellogenins are major egg yolk proteins responsible for providing nutrients required for embryonic development in egg-laying vertebrates and invertebrates. Certain components of vitellogenin, like the -component from chum salmon, can be major allergens in patients allergic to fish roe, with cross-reactivity to similar proteins in other salmonid fish roe.¹

Other enzymes

Several other enzymes involved in glycolysis, including triosephosphate isozyme, pyruvate kinase, lactate dehydrogenase, glucose-6-phosphate isozyme, and glyceraldehyde-3-phosphate dehydrogenase, have also been identified as minor allergens in fish.³

Recognising fish allergy symptoms:

Fish allergy symptoms can vary in severity from mild to severe, and they typically occur after exposure to proteins found in fish. These symptoms can manifest as immediate or delayed reactions.⁴

Here are some common symptoms of a fish allergy:

Immediate Allergic Reactions (usually within minutes to a few hours after exposure):

Skin reactions:

• Itching or tingling sensations in the mouth, lips, tongue, or throat
• Hives (raised, itchy welts) on the skin, which can appear anywhere on the body
• Redness and swelling of the skin, particularly around the face.

Respiratory symptoms:

• Wheezing (a high-pitched whistling sound during breathing)
• Coughing.
• Shortness of breath.
• Chest tightness.
• Runny or stuffy nose.
• Sneezing.

Gastrointestinal issues:

• Nausea.
• Vomiting.
• Abdominal pain or cramps.
• Diarrhoea.

Cardiovascular symptoms:

• Rapid or irregular heartbeat.
• Dizziness or lightheadedness.
• Drop in blood pressure (in severe cases).

Swelling:

• Swelling of the lips, tongue, throat, or face (angioedema)

Anaphylaxis (severe allergic reaction):

• Anaphylaxis is a rare but potentially life-threatening reaction characterised by a sudden drop in blood pressure, severe swelling of the throat and tongue, difficulty breathing, and loss of consciousness. It requires immediate medical attention and the administration of epinephrine (adrenaline).

Delayed Allergic Reactions (Usually Hours to Days After Exposure):

1. Skin Issues:
   • Eczema (atopic dermatitis) is characterised by red, itchy, and inflamed skin patches.
   • Rash or hives appearing after a delay.
2. Gastrointestinal Problems:
   • Persistent stomach discomfort.
   • Bloating.
   • Diarrhoea.
   • Gastritis (inflammation of the stomach lining)

It's important to note that the severity and combination of symptoms can vary among individuals with fish allergies. Some people may only experience mild symptoms, such as localised itching, while others may develop more severe reactions, including anaphylaxis.

How do doctors diagnose fish allergies?

Diagnosing fish allergies involves a combination of clinical assessment and specialised tests.^1,5
Here are the primary diagnostic methods for identifying fish allergies:

Clinical assessment:

• Comprehensive evaluation of the patient's medical history, including allergic reactions, symptoms, and exposure to fish.
• Detailed questioning about the timing and duration of allergic episodes, specific fish species consumed, and characteristics of the allergic reactions
• Assessment of prior histories of similar reactions.

Skin prick test (SPT):

• Skin prick testing involves applying small amounts of allergen extracts, including fish proteins, to the skin's surface.
• A tiny needle or lancet is used to introduce the allergen into the skin's top layer.
• If a patient is allergic to fish, they may develop a visible allergic reaction at the test site within 15–20 minutes.^1,5

Serum-specific IgE testing:

• This in vitro blood test measures the levels of specific IgE antibodies against fish allergens in the patient's blood.
• Elevated specific IgE levels may indicate sensitization to fish proteins and the potential for clinical reactivity.^1,5

Oral food challenge (OFC):

• OFC is the definitive in vivo test to confirm fish allergies.
• It involves the patient's supervised consumption of fish in a controlled clinical setting.
• A positive OFC result, characterised by allergic reactions, correlates with a strong likelihood of a fish allergy.^1,5

Elimination diet:

• Patients may be advised to follow an elimination diet by removing fish and fish products from their diet for a specific period of time.
• Improvement in symptoms during the elimination phase, followed by symptom recurrence upon reintroducing fish, can suggest a fish allergy.^1,5

Patch testing:

• Patch testing may be used to diagnose contact allergies related to fish, such as skin reactions upon handling fish or fish products.
• Small amounts of fish proteins are applied to patches and placed on the skin for a set duration to assess skin reactions.

These are some of the methods that doctors use to diagnose a fish allergy. If you suspect that you have a fish allergy, you should consult an allergist who can perform these tests and provide you with personalised advice on how to manage your condition and avoid potential triggers.

Living with a fish allergy

Living with a fish allergy requires careful management and awareness to minimise the risk of allergic reactions.^1,5
Here are important steps and considerations for individuals with a fish allergy:

Avoiding fish and cross-contamination

Reading food labels:

• Always scrutinise food labels for fish or seafood ingredients. Fish can be found in unexpected products like sauces, condiments, and even certain processed foods.
• Be vigilant about terms like "fish sauce," "anchovy paste," or "seafood flavouring," which may indicate fish components in a product.
• Look for allergen labelling such as "Contains: Fish" or similar warnings.

Dining out safely:

• When dining at restaurants, inform the staff about your fish allergy. Ask about their preparation methods and cross-contamination prevention.
• Be cautious when ordering dishes that involve frying or grilling, as cross-contamination can occur on shared cooking surfaces.
• Choose restaurants with a clear understanding of food allergies and dedicated allergy-friendly options.

What to do in an emergency

Using an epinephrine (EpiPen):

• Carry an epinephrine auto-injector (EpiPen) at all times. Ensure that you and your close contacts know how to use it.
• Administer the EpiPen immediately if you experience severe allergic symptoms, such as difficulty breathing, swelling, or a drop in blood pressure.
• Always follow up with emergency medical care, even after using the EpiPen, as its effects are temporary.

When to seek immediate medical help:

• Seek emergency medical assistance if you experience anaphylactic symptoms, including severe difficulty breathing, loss of consciousness, or a rapid, weak pulse.
• Do not delay in seeking professional help, as anaphylaxis can progress rapidly.

Informing family, friends, and carers:

• Ensure that your family members, close friends, and carers are aware of your fish allergy.
• Teach them how to recognise the signs of an allergic reaction and how to respond, including administering epinephrine if necessary.
• Provide them with emergency contact numbers and instructions for your healthcare team.

Creating a plan for emergencies:

• Develop an emergency action plan in consultation with your allergist or healthcare provider. This plan should outline steps to take in the event of an allergic reaction.
• Include details such as allergen avoidance strategies, the proper use of epinephrine, and when to seek medical attention.
• Ensure that copies of this plan are easily accessible at home, school, work, and other relevant locations.

Conclusion

Living with a fish allergy may present challenges, but with the right knowledge and support, you can lead a safe and fulfilling life. It's crucial to remain vigilant, read food labels diligently, and be prepared for emergencies with an epinephrine auto-injector. Connect with support groups and resources to learn from others who share similar experiences and stay up-to-date on the latest information and allergy-friendly recipes.

Remember that while managing a fish allergy requires attention, it should never hinder your ability to enjoy delicious meals and engage in the activities you love. With awareness, safety measures, and a positive outlook, you can savour a wide variety of allergen-free foods and live a life that's rich and rewarding.

If you or a loved one has a fish allergy, it's essential to work closely with healthcare professionals and allergists who can provide personalised guidance and support. Stay informed, stay safe, and embrace the opportunities that life has to offer, even with a food allergy.