Alpha-gal allergy is an allergy to meat products which manifests several hours after eating meat. It is caused by IgE-mediated antibody response to an oligosaccharide called galactose-alpha 1,3 galactose which is found on animal proteins from a variety of species. Allergic reactions to this oligosaccharide epitope can occur in an immediate or delayed fashion.
Symptoms of Immediate Hypersensitivity
Immediate reactions due to alpha-gal allergy may occur within as little as 20 minutes of intravenous administration of the monoclonal antibody cetuximab. Reactions are both rapid and often severe, and may sometimes be fatal. In most cases the drug can never be administered again to the affected individual.
Delayed Hypersensitivity Symptoms
Another type of hypersensitivity is manifested against the ingestion of red meat. It occurs in the form of urticaria, repeated episodes of anaphylaxis and angioedema, mostly in people who spend much time outdoors. They give a history of eating meat, either beef or pork, several hours earlier. Intradermal allergy testing for meat is strongly positive, and IgE for meat is found to be high. This is, therefore, designated red meat allergy. This group of patients also has high IgE levels against alpha-gal.
Organ meats, especially pork kidneys, cause both a more severe and rapid onset of anaphylaxis, as compared to red meat, which requires to be ingested in a larger amount to produce the same symptoms.
Alpha-gal Allergy vs Food Allergy
Symptoms of red meat allergy are distinctive enough to separate it from other food allergies. Like any food allergies, it produces urticaria and gut-related symptoms. However, the symptoms start at least 2-3 hours after the ingestion of the suspect food. Moreover, it is inconsistent, with symptoms not appearing each time the patient eats red meat. Many of these subjects may ingest meat-derived substances such as gelatin through many other food and non-food products without suffering ill effects. Most importantly, it is due to a carbohydrate antigen rather than a protein, and requires a tick bite to become manifest.
Symptoms of Alpha-gal Allergy
The most common symptom of alpha-gal allergy is severe pruritis, often over the whole body, especially of the palms and the plantar skin. This may often be associated with urticaria.
Many others have reported that they felt nausea, experienced diarrhea or had indigestion before the onset of the allergic reaction. Such symptoms are not a necessity, and many patients have no symptoms warning them of the onset of an allergy.
All patients have eaten red meat for years before the first attack of red meat allergy. In most patients, there is no history of atopy or allergic disorders. They also have no history of allergy following the ingestion of turkey, chicken or fish.
Other symptoms include the onset of anaphylaxis, including wheezing and respiratory difficulty, swelling, hypotension and generalized collapse. Children older than 5 most often present with urticarial rashes, or angioedema (allergic swelling of the lips and the throat).
Red meat allergy must be treated on an emergency basis because of the possibility of a multi-system and fatal anaphylactic reaction. Intramuscular epinephrine injection is required to arrest the reaction. This is the only drug which can act promptly to reverse the inflammatory changes underlying allergic manifestations, and should not be replaced by any other drug in cases of anaphylaxis. Repeat dosing is necessary if the response is suboptimal or the patient is refractory to the drug.
Bronchodilators, such as albuterol, are required to clear bronchoconstriction. These are beta-receptor agonists or topical steroids, and prevent airway narrowing in anaphylaxis. They may be administered via nebulization or a metered dose inhaler.
In addition, corticosteroids and antihistamines, with oxygen administration, may be required if the reaction is more severe. These drugs prevent mast cell and basophil degranulation which releases the mediators of inflammation during an allergic inflammation. Other vasopressor drugs may be required to treat the hypotension in addition to intravenous fluids. Drugs like atropine may also be given if bradycardia is present, and glucagon to provide adequate blood sugar levels.
Once this condition has been recognized, patients should carry an auto-injection device containing epinephrine (EpiPen) with them for prompt treatment. In addition, they should seek prompt medical care if they develop any symptoms following the ingestion of food. They are advised to avoid tick bites because the antibody levels slowly decline over time. Thus some patients who have had red meat allergy are later able to tolerate red meat after several years without a tick bite.