Alpha-Gal Syndrome: A Tickborne Allergy to Red Meat
“We estimate as many as 450,000 people may be living with alpha-gal syndrome in the U.S. And the number of positive tests has been going up year by year.”
- Gilbert Kersh, Ph.D., Division of Vector-Borne Diseases, Centers for Disease Control and Prevention
“Nothing will benefit human health and increase the chances for survival of life on Earth as much as the evolution to a vegetarian diet.”
- Albert Einstein
Never heard of alpha-gal syndrome (AGS)? You’re not alone. On July 28, 2023, the Centers for Disease Control and Prevention (CDC) issued a report indicating that 42% of health care providers had never heard of the condition. In this Germ Gems’ post, I focus on AGS, an emerging, tick bite-induced allergy characterized by a potentially life-threatening immune reaction to the carbohydrate galactose-alpha-1,3-galactose (“alpha-gal”) found in red meat and other products made from mammals, e.g., gelatin, cow’s milk and milk products.
What is AGS? AGS is an allergic reaction to alpha-gal, a sugar molecule found in most mammals including cows, bison, deer, pigs, sheep, and lambs but not humans. Ticks can, however, transfer the alpha-gal molecule (an allergen) from another mammal to a human.
In the U.S., the lone star tick is the vector. If this tick bites you, it can transfer the alpha-gal molecule to you making your immune system sensitive to this molecule (allergen) the next time your body encounters it. If you then eat red meat, you may develop AGS—an immunoglobulin E (IgE)-mediated reaction to the alpha-gal molecule. (AGS is also called “red meat allergy,” “mammalian meat allergy,” or “tick bite meat allergy.”)
In 2002, University of Virginia allergist Thomas Platts Mills first formally identified the allergy as originating from tick bites. He linked the disease to the lone star tick (Amblyomma americanum). In 2007, Sheryl van Nunen, an Australian allergist, independently discovered AGS but identified the tick Ixodes holocyclus as the vector. (For an excellent overview of AGS, see “Red Meat Allergy Caused by Tick Bite Is Spreading—and Nearly Half of Doctors Don’t Know About It” and “Meat Eaters Beware,” in the August 7, 2023, issue of Scientific American.)
Epidemiology of AGS. As is the case with other vector-borne diseases, AGS is facilitated by global warming which expands the breeding conditions for ticks and mosquitoes. In the U.S., the geographic distribution of AGS overlaps that of the habitat of the lone star tick.
According to the CDC, the number of cases in the U.S. has increased substantially since 2010 reflecting the establishment of lone star ticks throughout Arkansas, Kentucky, Missouri, and Suffolk County, New York. (In Minnesota, the lone star tick is one of three tick species that people may encounter—the deer tick and wood tick being the other two.) Estimates based on surveillance with antibody testing suggest that AGS has affected roughly between a hundred thousand to nearly half a million people in the U.S. since 2010 and that number of cases is steadily growing.
What are the symptoms of AGS? Like other IgE-mediated allergies, AGS symptoms include severe whole-body itching, hives, angioedema, gastrointestinal upset, and possible anaphylactic shock. In 70% of the cases, respiratory distress occurs—a condition particularly harmful to asthmatics. In contrast to the typical rapid onset of most food allergies, the reaction to alpha-gal is delayed, occurring three to eight hours after the consumption of mammalian products. The diagnosis of AGS is confirmed by a blood test for IgE antibodies to alpha-gal.
Treatment and prevention of AGS. There’s no treatment or cure for AGS. Patients can manage their condition by avoiding foods that contain the alpha-gal molecule including all “red meat” (e.g., beef, pork, lamb, rabbit, horse, goat, venison, and bear) as well as many prepackaged food items made from mammals and dairy products. (For a complete list of what to avoid, visit the Internet site Allergy Insider “Alpha-Gal Syndrome Allergen Facts, Symptoms, and Treatment.”) Becoming a vegetarian or vegan are options. I doubt, however, that the vegetarian/vegan strategy would appeal to the young man who was sitting at a table near me at the Neue Museum in New York City wearing a t-shirt with this message:
“I didn’t claw my way to the top of the food chain to eat vegetables.”
Fortunately, for any AGS patients that may share this sentiment, the alpha-gal molecule is not found in fish, reptiles, or birds. So eating fish and poultry are still options.