Alpha-gal syndrome

Alpha-gal syndrome is an unusual form of food allergy in which patients develop an IgE-mediated reaction to galactose-α-1,3-galactose, usually shortened to alpha-gal. Alpha-gal is a carbohydrate found in the tissues of most non-primate mammals. Unlike conventional food allergy, reactions are often delayed for several hours after eating mammalian meat.

🕷️ What causes alpha-gal syndrome?

The condition is strongly associated with tick bites. Tick saliva appears to stimulate production of IgE antibodies against alpha-gal. Subsequent exposure to alpha-gal in food or other mammalian-derived products may then trigger an allergic reaction. In the United States, the lone star tick is particularly associated with alpha-gal syndrome. Other tick species have been implicated in Europe, Australia and elsewhere. The condition can therefore occur in the UK, although it is much less commonly recognised than in some parts of the United States.

🥩 Which foods contain alpha-gal?

• 🥩 Beef 🐑 Lamb and mutton 🐖 Pork 🦌 Venison
• 🐇 Rabbit 🫀 Offal from mammals 🍮 Gelatin and some gelatin-containing foods
• 🥛 Some mammalian-derived food products

Poultry, fish and seafood do not contain alpha-gal and are generally tolerated. Dairy products contain smaller amounts of alpha-gal and many patients can tolerate milk and dairy, although patients with more severe disease may react to them.

⏰ Why is the reaction delayed?

Most IgE-mediated food allergies cause symptoms within minutes because allergenic proteins are absorbed relatively quickly. Alpha-gal is mainly associated with glycolipids and other lipid-containing molecules. These are processed and absorbed more slowly through the gastrointestinal tract and lymphatic system, which probably explains why reactions frequently occur 2 to 6 hours after eating. This delay is an important diagnostic clue. A patient may eat steak in the evening and develop urticaria, abdominal symptoms or anaphylaxis during the night, making the association with food less obvious.

⚠️ Clinical features

• 🔴 Urticaria 🖐️ Generalised pruritus 😮 Angioedema
• 🤕 Abdominal pain 🤢 Nausea or vomiting 🚽 Diarrhoea 🫁 Wheeze or breathlessness
• 💫 Dizziness or hypotension 🚨 Anaphylaxis

Some patients predominantly develop gastrointestinal symptoms without obvious urticaria or respiratory symptoms. This can lead to investigation for gastrointestinal disease before the allergic mechanism is recognised.

🔍 When should you suspect alpha-gal syndrome?

Consider alpha-gal syndrome in a patient with otherwise unexplained recurrent urticaria or anaphylaxis, particularly when episodes occur several hours after eating red meat. A history of tick bites or frequent exposure to wooded or rural environments strengthens the suspicion.

• ⏱️ Reactions typically occur several hours after exposure.
• 🥩 Beef, pork, lamb and venison are common triggers.
• 🌙 Symptoms may occur during the night after an evening meal.
• 📈 Severity can vary considerably between episodes.
• 🕷️ There may be a history of recent or repeated tick bites.

📈 Why can the severity vary?

The amount of alpha-gal consumed is only one determinant of the reaction. Fatty meals may produce more significant reactions because lipid absorption is important in transporting alpha-gal-containing molecules. Alcohol, exercise and NSAIDs may also act as cofactors and lower the threshold for a reaction.

🧪 Diagnosis

The diagnosis is based on the characteristic clinical history together with evidence of IgE sensitisation to alpha-gal.

• 🗣️ Take a detailed history of the timing of symptoms in relation to mammalian meat.
• 🕷️ Ask specifically about tick bites.
• 🧪 Measure serum specific IgE to alpha-gal where available.
• 🥩 Consider specific IgE testing to beef, pork or lamb as supportive evidence.
• 🔍 Exclude alternative causes of recurrent urticaria or anaphylaxis where appropriate.

A positive alpha-gal IgE test indicates sensitisation but must be interpreted alongside the clinical history. Some people may have detectable antibodies without clinically significant reactions.

💊 Management

The main treatment is avoidance of foods that trigger reactions. The degree of avoidance required varies between patients.

• 🚫 Avoid beef, pork, lamb and other mammalian meat.
• 🥛 Assess whether gelatin or dairy products also cause symptoms.
• 📋 Provide an emergency management plan.
• 💉 Patients at risk of anaphylaxis should usually carry adrenaline auto-injectors.
• 🎓 Teach patients how and when to administer intramuscular adrenaline.
• 🕷️ Encourage measures to reduce further tick bites.

🚨 Treatment of an acute reaction

Anaphylaxis associated with alpha-gal syndrome is managed in exactly the same way as anaphylaxis from other causes. Intramuscular adrenaline is the first-line treatment.

• 💉 Give intramuscular adrenaline promptly when anaphylaxis is suspected.
• 📞 Position the patient appropriately and call for emergency help.
• 🫁 Give oxygen and intravenous fluids when clinically indicated.
• 🔁 Repeat intramuscular adrenaline if there is an inadequate response.
• 💊 Antihistamines may help urticaria but must not delay adrenaline in anaphylaxis.

💉 Medicines and medical products

Alpha-gal is also relevant to medicine because some pharmaceutical and biological products are derived from mammals. The clinical significance varies considerably between patients and between products.

• 💊 Gelatin-containing medicines and vaccines may occasionally cause reactions.
• 🩸 Some heparin preparations are derived from porcine tissue.
• 🧬 Biological products manufactured using mammalian cells may contain alpha-gal epitopes.
• ❤️ Bioprosthetic heart valves are commonly derived from porcine or bovine tissue.

These products should not automatically be withheld from every patient with alpha-gal syndrome. The clinical history, severity of previous reactions and the importance of the proposed treatment should be considered, with allergy specialist advice where necessary.

🧬 Cetuximab and alpha-gal

Cetuximab provides an important historical link to the discovery of alpha-gal allergy. Some patients developed severe immediate hypersensitivity reactions to their first cetuximab infusion. Investigators subsequently demonstrated that these patients already had IgE antibodies against alpha-gal present on the cetuximab molecule. This observation helped establish the association between tick exposure, alpha-gal sensitisation and mammalian meat allergy.

🔄 Does alpha-gal syndrome resolve?

Alpha-gal IgE concentrations may gradually fall if further tick bites are avoided. Some patients eventually regain tolerance to mammalian meat, although this can take several years. Further tick bites may increase antibody levels again and lead to recurrence or worsening of reactions.

⭐ Key points

• 🧬 Alpha-gal syndrome is an IgE-mediated allergy to the carbohydrate galactose-α-1,3-galactose.
• 🕷️ It is strongly associated with previous tick bites.
• 🥩 It typically causes delayed reactions after eating mammalian meat.
• ⏰ Symptoms usually begin 2 to 6 hours after exposure rather than immediately.
• ⚠️ Clinical features range from gastrointestinal symptoms and urticaria to severe anaphylaxis.
• 🧪 Diagnosis is supported by serum specific IgE to alpha-gal.
• 💉 Treatment is avoidance of relevant mammalian products and standard emergency treatment of anaphylaxis.
• 🕷️ Further tick bites should be avoided because they may maintain or increase sensitisation.