Does your mouth water at the thought of a visit to your favorite steakhouse? Or maybe you prefer things a bit more low-key, and your perfect weekend involves a barbecue with family and friends, with some juicy steaks and meaty ribs on the grill. If you’re a dedicated carnivore who enjoys the taste, smell, and maybe even the nutritional benefits of beef, lamb, and other animal foods, give a moment of thought to people who are allergic to meat. It’s true! Such a thing exists!
This once rare but increasingly common allergy is induced by a bite from Amblyomma americanum, a.k.a. the Lone Star tick. The allergy (IgE-mediated) is due to sensitization to a sugar called Alpha-Gal (short for galactose-alpha-1, 3-galactose, or α-Gal). α-Gal is a component of glycoproteins in mammals. However, during evolution, primates and humans lost the enzyme required to produce α-Gal (galactosyltransferase), and this disaccharide is now immunogenic to humans.
According to a Vanderbilt University immunology fellow, “You’re walking through the woods, and that tick has had a meal of cow blood or mammal blood. The tick, carrying Alpha-Gal, bites you and activates your allergy immune system.” The body creates antibodies to Alpha-Gal, and from then on, the body will react to these molecules, which are contained primarily in mammalian proteins. Affected individuals can typically still safely consume seafood and fowl, so finfish, shellfish, chicken and turkey are usually okay, but beef, pork, lamb, goat, venison and other mammalian proteins are off the menu.
For individuals with the Alpha-Gal allergy, it’s not enough to avoid the meats they’re allergic to. They must also be vigilant about their snack foods, supplements, medication and even vaccines. These items may contain mammal-sourced gelatin or α-Gal, and can induce an allergic response in those sensitive to it. Not all people with Alpha-Gal allergy are sensitive to gelatin, but many are. Some will react to gelatin-containing vaccines, but there have been reports of some tolerating them without a problem.
Identifying this intriguing allergy isn’t easy. Some individuals may have an anaphylactic reaction upon exposure to mammalian proteins, but the more common symptoms are things that could be attributed to any number of other causes. These include hives or skin rash, nausea, stomach cramps, indigestion, vomiting, diarrhea, stuffy or runny nose, sneezing, headaches, or asthma. Making matters even more complicated, some of these symptoms are delayed, rather than immediate: they don’t affect an individual until the food is digested and the offending substance enters the bloodstream, hours after consumption. The appearance of non-specific symptoms as much as six hours after a meal makes it difficult to connect the symptoms to any particular food, so for people who don’t have an anaphylactic reaction, it can take multiple repeated exposures and reactions to realize meat is the cause.
Additionally, individual reactions and symptom severity may vary. Organ meats and innards contain higher amounts of α-Gal than muscle meats do, so reactions may be worse if an affected person consumes more organ meats.
Why is α-Gal allergy on the rise? It was originally limited to the southeastern US, but it’s becoming more common farther north and west as the climate warms. The natural habitat of the Lone Star tick is the southeastern US, but the insect can now be found as far north as New England and as far west as Kansas, and cases of α-Gal allergy have been recorded as far from the south as Long Island, NY and Minnesota. Speaking about his clinic, the immunologist quoted earlier said in 2017, “Five years ago, we probably had about 50 or so patients that had Alpha-Gal [syndrome]. Now we have about 200.” Outside the US, there have been case reports in Australia, Japan, Western Europe, and Central America. Reports from Sweden have implicated another tick species, Ixodes Ricinus (the castor bean tick), in this allergy, so the Lone Star tick isn’t the only vector. All Swedish patients with the allergy were bitten by ticks.
There is no treatment for α-Gal allergy other than drugs that may help ameliorate the symptoms. However, in some individuals, the allergy may lessen or even disappear altogether in about 3-5 years if they don’t get bitten by the tick again. There’s no guarantee of that, though, so the best bet is to take precautions with protective clothing and compounds when spending time outdoors.