Tick-borne red meat allergy (α-gal syndrome)

Samira Jeimy; Rongbo Zhu

doi:10.1503/cmaj.231067

Tick-borne red meat allergy occurs from sensitization to a carbohydrate, galactose-α-1,3-galactose (α-gal)

The lone star tick (Amblyomma americanum) is commonly found in the southern United States, but its prevalence in Canada is increasing.1 The tick’s saliva contains a high level of α-gal, a carbohydrate antigen also present in nonprimate mammalian cell membranes.2 Skin and bloodstream exposure to this antigen through a tick bite leads to sensitization to the carbohydrate and, subsequently, to red meat allergy.

In addition to food sources like red meat, health care–related exposures can trigger α-gal syndrome

In 2023, the US Centres for Disease Control and Prevention declared α-gal syndrome a public health concern.2 Patients can develop anaphylaxis from unexpected sources of α-gal exposure including vaccines (e.g., live herpes zoster vaccine; measles, mumps and rubella vaccine), supplements (e.g., collagen), medications (e.g., heparin, cetuximab) and heart valve replacements (Box 1).3

Box 1: Potential sources of α-gal antigen

Foods

Red meat (e.g., beef, pork, lamb)
Animal viscera (e.g., kidney, liver, heart, intestine)
Sausage casing
Dairy (e.g., milk, cheese, yogurt, butter)
Animal-based shortening (e.g., lard, tallow)
Gelatin-containing snacks (e.g., marshmallows, gummy bears, fruit snacks)

Supplements

Collagen

Vaccines

Gelatin-containing vaccines (e.g., live herpes zoster; measles, mumps and rubella; yellow fever)

Prescription medicine

Pancreatic enzyme replacement
Monoclonal antibodies (e.g., cetuximab)

Medical products

Gelatin-based colloid plasma substitute (e.g., gelafundin)
Heparin (sourced from porcine intestine)
Bovine and porcine heart valves

Diagnosis of α-gal syndrome is challenging, given its spectrum of presentations

Unlike other food allergy reactions to protein antigens, α-gal reactions are delayed and occur up to 8 hours following ingestion of red meat. Symptoms can include urticaria, angioedema and respiratory, gastrointestinal and cardiovascular manifestations of anaphylaxis.4 Some patients have only gastrointestinal symptoms, leading to a misdiagnosis of food intolerance rather than allergy. Diagnosis of α-gal syndrome has increased among patients previously thought to have idiopathic anaphylaxis.5

Clinicians should consider α-gal syndrome in the differential diagnosis of unusual food or drug reactions

A new onset of reactions to red meat (an uncommon allergen) should alert clinicians to suspect α-gal syndrome. Diagnosis requires a thorough clinical assessment along with immunoglobulin (Ig) E testing, which is commercially available.

Management is similar to that of other IgE-mediated allergies

Patients with α-gal syndrome should avoid all red meat and α-gal–containing products, but can safely consume white meat and fish. Patients should carry an epinephrine autoinjector and obtain a medical alert bracelet. Immunotherapy to induce desensitization is not yet available.

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Footnotes

Competing interests: Samira Jeimy reports research funding from the Academic Medical Organization of Southwestern Ontario and Schulich School of Medicine and Dentistry, as well as consulting fees and honoraria from Sanofi, GSK, Miravo, AstraZeneca, Medexus, Stallergenes Greer and Novartis. She is a clinical expert with the Canadian Agency for Drugs and Technologies in Health, vice-chair of the Allergy and Clinical Immunology section of the Ontario Medical Association, chair of the Women in Medicine committee of the Ontario Medical Association, co-chair and planning member of the Canadian Women in Allergy and Clinical Immunology annual conference and founding member of Focused COVID Communications. Rongbo Zhu reports honoraria for lectures from AstraZeneca, GSK, Medexus Pharmaceuticals, Sanofi, StallergenesGreer and ValeoPharma, as well as participation on data safety monitoring boards for Bausch Health and ValeoPharma. No other competing interests were declared.
This article has been peer reviewed.

This is an Open Access article distributed in accordance with the terms of the Creative Commons Attribution (CC BY-NC-ND 4.0) licence, which permits use, distribution and reproduction in any medium, provided that the original publication is properly cited, the use is noncommercial (i.e., research or educational use), and no modifications or adaptations are made. See: https://creativecommons.org/licenses/by-nc-nd/4.0/

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