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Alpha Gal Allergy

Alpha-gal (galactose-α-1,3-galactose) is a sugar molecule present in most non-primate mammals but not in fish, reptiles, birds, or people. Patients appear to be sensitized through the bites of Lone Star tick, Amblyomma Americanum, whose host is deer. These ticks are most prevalent in the lower Midwest, Southeast, mid-Atlantic, and Northeast United States. 

When a sensitized human eats mammalian meat or mammalian-derived products, alpha-gal is absorbed by the GI tract bound to glycolipid, and incorporated into chylomicrons, which enter the circulation in approximately 2 hours. When alpha-gal binds to IgE antibodies present on mast cells in the GI tract, the mast cells degranulate and release histamine and other immune mediators. These mediators bind to sensory nerve endings causing abdominal pain, intestinal smooth muscles contractions, and mucous gland secretion.

 

Alpha-gal syndrome typically occurs 2 to 6 hours after a person eats beef, pork, other mammalian meat, or other food products made from mammals. Symptoms include abdominal pain, diarrhea, nausea and vomiting.

While the most common presentation is a delayed allergy to meat, anaphylaxis to alpha-gal has been reported after routine childhood vaccinations, possibly due to gelatin and/or calf serum in the vaccines. Other products, including colloid solutions, gelatins, bovine or porcine heart valves, and possibly some hemostatic agents, have also been implicated.

Diagnosis of the alpha-gal syndrome can be confirmed by testing for IgE antibodies to alpha-gal. Patient who test positive for IgE antibodies to alpha-gal should be instructed to adopt an alpha-gal avoidance diet that eliminates beef, pork, venison and related products such as lard, dairy, and ice cream. If patients are able to avoid tick bites, it may be reasonable to repeat alpha-gal IgE levels 6 to 12 months after diagnosis. As the IgE level decreases or becomes negative, patients may be able to resume eating dairy, and then mammalian meat products. 

References

Stone CA, et al. Anaphylaxis after vaccination in a pediatric patient: further implicating alpha-gal allergy. J Allergy Clin Immunol Pract 2019; 7:322

McGill SK et al. AGA Clinical Practice Update on Alpha-Gal Syndrome for the GI Clinician: Commentary. Clin Gastroenterol Hepatol. April 2023, 21 (4) 891-896.

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