Summary

α-Gal-associated meat allergy is a recently described syndrome in which individuals who have been bitten by ticks of the Ixodidae family become sensitized to the carbohydrate determinant galactose-α-1,3-galactose (α-Gal). The resulting IgE antibodies react with α-Gal epitopes on mammalian meat, resulting in an allergic reaction and in some cases anaphylaxis after eating meat or gelatin. A distinctive feature of this allergy is the delayed onset of symptoms, which occurs 2-6 hours after eating meat. The delayed symptom onset is thought to reflect the appearance of glycolipid α-Gal moieties, which are believed to be involved in the allergic reaction, in the bloodstream.

Diagnosis of α-Gal-associated meat allergy may not be straightforward, especially in children, as the syndrome can be confused with protein-based meat allergies. While negative skin prick test (SPT) results are unreliable, the syndrome can be confirmed by correlating clinical history with the measurement of IgE antibodies to α-Gal. If α-Gal sIgE results represent >2% of total sIgE, a diagnosis of meat allergy is very likely. Serum tryptase testing can help identify people who may have more severe reactions to tick bites. Finally, testing for the presence of IgE to α-Gal could identify a risk factor for medical treatment with cetuximab, eating gelatin-containing substances, or using artificial bovine blood in areas where hard body ticks are common, particularly in individuals with a history of a tick bite or demonstrated allergy to mammalian meat or gelatin.

Diagnostics

Disease Severity

Delayed onset of symptoms is the most clinically distinguishing characteristic of α-Gal-associated meat allergy compared with protein-based meat allergies. However, accurate information on the timing of symptom onset is not always available from the patient.

Exposure

Alpha-Gal is present in all mammals except for humans and old-world monkeys. Therefore, red meats such as beef, pork, and lamb are the most common triggers. But derivatives of red meat can be hiding in a variety of foods that aren’t always clearly labeled, like gelatin-containing foods and dairy. These derivatives can also be found in many medications and biologic therapies of which patients need to be aware.

Not all triggers are equally likely to cause a reaction—see the chart below for triggers ranked from higher to lower risk.

Table 2. Adapted from

There are also cofactors that may increase the risk or severity of the reaction, including:

Prevention And Therapy

Management of α-Gal-associated meat allergy

The primary management strategy is avoiding mammalian meat, especially fatty cuts.

Although most patients tolerate dairy products and gelatin, patients who continue to have unexplained symptoms may also be advised to avoid dairy foods and gelatin.

Avoid additional tick bites by staying away from tick-infested areas, wearing protective clothing, or using products containing N, N-diemethyl-meta-toluamide may make some patients less prone to symptomatic reactions.