"Alpha-gal" is a kind of carbohydrate that occurs in mammals (but not humans or other apes). Its technical name is galactose-alpha-1,3-galactose. And "alpha-gal syndrome" is also called mammalian meat allergy. It can be caused by contact with mammal meat. But it can also be spread by certain ticks, e.g., Amblyomma americanum oder Ixodes ricinus. Other animals who aren't mammals (e.g., chickens, fishes, reptiles, etc.) do not contain alpha-gal. Most allergies are triggered by specific protein molecules, not specific carbohydrate molecules.
A case of a vegan in the United States with this "syndrome" has just been reported by Wong et al. (2024). The vegan "suffered" from a swollen eyelid. This symptom went away without treatment after "a few weeks".
What is alpha-gal syndrome (i.e., mammalian meat allergy)?
"Recently, a new inflammatory and allergic syndrome called alpha-gal syndrome has been described. Exposure to mammalian meat products can precipitate [i.e., cause] orbital [i.e., eye socket] inflammatory disease, but many [non-vegan] food and [non-vegan] nonfood products in the United States contain the alpha-gal oligosaccharide. Thus the disorder can occur even in vegetarians and vegans. [This explanation is not exactly clear. (1) Lacto-ovo-vegetarians are exposed to mammalian products, i.e., dairy products. How vegans who avoid all animal products including gelatine could be exposed to alpha-gal appears uncertain - possibly through contamination or involuntary/accidental contact with animal products, e.g., medication in gelatine capsules.]
A 65-year-old South Asian male [vegan] presented with 3 episodes of recurrent, unexplained bilateral diffuse swelling of the left upper lid. Past medical history included psoriasis and asthma. The remainder of the past medical, surgical, and family histories were noncontributory. The patient was a strict vegan.
[...]
Serum beef alpha-gal IgE (i.e., immunoglobulin E, which is a type of antibody) was elevated at 0.16 kU/L (normal, <0.10 kU/L). Over the next few weeks (Fig. 2) the patient had gradual and complete resolution of his OIS [orbital inflammatory syndrome] without treatment.
[...] On direct questioning, the patient denied any alpha-gal-containing agent exposure."
Below several products that may contain "alpha-gal" are listed:
- Cow's milk
- Beef- or pork-derived gelatin (made from the bones, cartilage, and skin of cattle and pigs)
- Products containing lard, tallow, or suet (apparently, this is what suet is: "the hard fat about the kidneys and loins in beef and mutton that yields tallow")
- Bouillon, gravy, and meat stock
- Gelatin-containing vaccines, capsules, plasma substitutes
- Glycerin (made from slaughtered mammals)
- Magnesium stearate (non-vegan magnesium stearate seems uncommon in the 21st century: "Classification: Vegan* Although it is possible to derive magnesium stearate from animal fats, it is not standard practice today in the food industry and no examples of tallow-derived magnesium stearate in foods or pharmaceuticals are known" [Vegetarian Resource Group 2015])
- Heparin (which is made from pig's intestine)
- Monoclonal antibodies, most notably cetuximab
- Bovine and porcine heart valves
- Catgut sutures
"[...] alpha-gal syndrome is an allergic inflammatory condition that can mimic [idiopathic (i.e., with unknown reason) orbital inflammatory syndrome] and may present with unilateral or bilateral periorbital edema. The diagnosis is made by elevated anti-alpha-gal IgE [blood] levels, [...] The etiology [i.e., cause] of [alpha-gal syndrome] is thought to be related to a bite from Amblyomma americanum (the lone star tick). Galactose-alpha-1,3-galactose oligosaccharide (i.e., alpha-gal) is found in the blood of most mammals, and human exposure occurs by transfer from a tick-bitten mammal to a human through tick saliva. The lone star tick is endemic to much of the eastern United States, and thus cases of [alpha-gal syndrome] generally follow this geographic distribution. Symptoms of this mammalian meat allergy are usually similar to an IgE-mediated type 1 hypersensitivity reaction, with gastrointestinal distress, hives, facial edema, and in severe cases anaphylaxis. However, unlike most anaphylactic reactions, the onset of symptoms is often delayed by 2–6 hours.
This can lead to delay in diagnosis because patients (and physicians) do not recognize the temporal relationship between exposure and onset of symptoms and signs. In addition, the development of [alpha-gal syndrome] in response to meat may be unpredictable, though recently acquired tick bites may be a risk factor for increased sensitivity. Development of [alpha-gal syndrome] is not exclusive to meat, and consumption of animal-derived products such as gelatin also may trigger a response, which may explain the patient's relatively rare occurrence in the setting of strict veganism.
[...]
The treatment of [alpha-gal syndrome] is preventative avoidance of triggers and diet modification [i.e., no mammal products]. Patients also should be counselled on the other non-food-related products that can trigger [alpha-gal syndrome]. Although desensitization to alpha-gal has been reported in the literature, the treatment remains unproven.
Patients with recurrent eyelid edema and orbitopathy [i.e., eye socket disease] may have angioedema related to antibody-mediated hypersensitivity reactions to alpha-gal. Clinicians should consider serum alpha-gal antibody levels [i.e., a blood test assessing those antibodies] in such cases so that preventative measures can be taken to avoid recurrent reactions including potentially life-threatening anaphylaxis." (Wong et al. 2024)
It appears conceivable that the symptoms in this vegan (described above) were relatively mild because the amount of alpha-gal he was exposed to (possibly through contamination of his food) was quite low.
Reference
- Calvin W Wong, Noor A R Laylani, Pamela Davila-Siliezar, Andrew G Lee: Alpha-gal-related bilateral orbital inflammatory syndrome in a strict veganCan J Ophthalmol. 2024 Mar 18:S0008-4182(24)00058-9. doi: 10.1016/j.jcjo.2024.02.011. Online ahead of print. https://pubmed.ncbi.nlm.nih.gov/38513715/
