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Alpha-gal allergy — or mammalian meat allergy — is a type of meat allergy characterized by a delayed onset of symptoms after ingesting mammalian meat and resulting from past exposure to tick bites. It was first reported in 2002. Symptoms of the allergy include rash, hives, nausea or vomiting, difficulty breathing, drop in blood pressure, dizziness or faintness and severe stomach pain.
Alpha-gal allergy is a reaction to the carbohydrate galactose-alpha-1,3-galactose , whereby the body is overloaded with immunoglobulin E antibodies on contact with the carbohydrate. Anti-gal is a human natural antibody that interacts specifically with the mammalian carbohydrate structure gal alpha 1-3Gal beta 1-4GlcNAc-R. The alpha-gal molecule is found in all mammals except catarrhines , the taxonomic branch that includes humans.
Bites from certain ticks, such as the lone star tick in the US, and the paralysis tick in Australia, which can transfer this carbohydrate to a victim, have been implicated in the development of this delayed allergic response to consumption of mammalian meat products. Individuals with alpha-gal allergy do not need to become strict vegetarians, because poultry, fish, and in rare cases for some people, lean meat such as venison does not trigger a reaction.
Alpha-gal allergy has been reported in 17 countries on all six continents where humans are bitten by ticks, particularly the United States and Australia. As of November 2019 Australia has the highest rate of mammalian meat allergy and tick anaphylaxis in the world. In the US, the allergy most often occurs in the central and southern regions, which corresponds to the distribution of the lone star tick. In the Southern United States, where the tick is most prevalent, allergy rates are 32% higher than elsewhere. However, as doctors are not required to report the number of patients with alpha-gal allergy, the true number of affected individuals is unknown. Alpha-gal has also been shown to exist in the saliva of Ixodes scapularis but not Amblyomma maculatum.