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A red meat allergy linked to tick bites may be affecting as many as 450,000 people, according to a new study released by the Centers for Disease Control and Prevention (CDC) on July 27.
But it’s likely that number is a significant underestimate of how many people actually have the allergy, known as alpha-gal syndrome. A CDC survey released the same day found that nearly 4 out 5 of healthcare providers had little or no knowledge of the condition. Only 5 percent of the providers surveyed felt “very confident” in their ability to diagnose or manage patients with AGS.
“AGS refers to the allergy that can develop following lone star tick bites and causes delayed allergic reactions to beef, pork, lamb, venison, and other forms of mammalian meat and other derived products such as dairy and gelatin,” says Scott Commins, MD, PhD, an associate chief of allergy and immunology at the University of North Carolina at Chapel Hill, and the medical director of the UNC Allergy & Immunology Clinic. Dr. Commins is the coauthor of both studies.
How Common Is Alpha-Gal Syndrome?
The overall prevalence of the allergy hasn’t been known until now. The current report established that more than 110,000 individuals have now tested positive for alpha-gal. Extrapolating from that to the general population, the study estimates that about 450,000 people could be affected in the United States alone, says Commins.
Prevalence likely varies considerably depending on geography. Since the condition is linked to the lone star tick, the condition is more common in areas where the tick is usually found. There are many cases in the mid-Atlantic, for example, but very few cases in areas of high elevation or on the West Coast, where lone star ticks are not known to be present, he says.
What Are the ‘Unusual’ Symptoms of Alpha-Gal Syndrome?
One of the many unusual features of AGS is that the symptoms don’t occur until two to six hours after a person eats meat. “Food allergy traditionally occurs within 5 to 30 minutes after eating the food,” says Commins.
Those symptoms can vary, including nausea, diarrhea, heartburn or indigestion, hives, and even anaphylactic shock (a severe, potentially life-threatening allergic reaction).
Providers are also observing more people with the condition who have GI symptoms but don’t develop more “typical” allergic symptoms such as a rash or swelling, according to the authors of the report.
Another unusual feature of AGS is that many people with the allergy don’t have a reaction every time they eat red meat, says Patricia Lugar, MD, an allergy and immunology specialist at Duke Health in Durham, North Carolina, who diagnoses and treats AGS. “A person may eat a beef empanada one day — with a small amount of meat — and not have a reaction, but on another day eat a steak followed by a slice of cheesecake and have a very serious reaction that sends them to the emergency room,” she says.
A clinical practice update on AGS for GI doctors was published in April 2023 in Clinical Gastroenterology and Hepatology.
Doctors Were Long Skeptical About the Existence of Red Meat Allergies
Researchers first began to observe a relationship between red meat allergies and tick bites more than a decade ago, when they identified patients who had allergic reactions such as hives or anaphylaxis after eating beef or pork and had also been bitten by a tick.
Alpha-gal is a sugar molecule found in most mammals, including cows, lambs, and pigs. It can also be found in the saliva of ticks.
Humans don’t make alpha-gal, so it’s foreign to our bodies, explained Commins in a UNC information sheet about the allergy.
“Our immune system can be tricked into making an allergic response to this sugar,” said Commins. After a person is sensitized to alpha-gal, they can get a reaction every time they eat red meat, he explained.
For many years, many members of the medical community had a hard time believing that people could be allergic to meat, and that it could be caused by a tick, says Dr. Lugar.
“I understand how, if you’re not originally exposed to these patients, if you’re not managing patients with recurrent sort of mysterious allergic reactions, that it’s very hard to believe that this is what’s going on. It seems quite fantastical,” she says.
But if you read the science and you understand how this hypersensitivity develops, how the disorder seems to be focused where the tick is found, and that with eliminating mammalian exposure, symptoms improve, it all starts to make sense, she says.
Causes and Risk Factors of Alpha-Gal Syndrome
People who get multiple tick bites (four or more), live near woodlands, and spend several hours a week outdoors in wooded areas are most at risk for alpha-gal, according to a paper published in the November 2022 Annals of Allergy, Asthma & Immunology.
People with AGS often have other allergies, too, says Lugar.
Among the people who were diagnosed with AGS, 75 percent recalled a tick bite, according to a study published in Gastroenterology in January 2021. The authors point out that the lone star tick can bite in the larval stage, when it’s only 0.5 millimeter (mm) to 1 mm long.
Why is it that there have been U.S. cases of AGS in areas where the lone star tick typically isn’t found? “There is some evidence of lone star ticks moving into the Great Lakes area, and the central-western migration of white-tailed deer is likely to expand the range of the ticks,” says Commins. It could also be that these cases are among people who got bitten during travel to parts of the country where the tick is found, he adds.
Other ticks and potentially even parasites that are found outside the United States have also been linked to the allergy, says Commins.
Alpha-Gal Syndrome Can Be Challenging to Diagnose
Alpha-gal syndrome is diagnosed by an allergist or other healthcare provider and requires a thorough history with compatible symptoms, and diagnostic testing with a test called IgE to alpha-gal. This detects the presence of an allergic antibody directed against the alpha-gal sugar, says Commins.
Because symptoms are delayed — often there is no food ingestion for three to six hours before symptoms — patients are often told they don’t have a food allergy or that it’s IBS or anxiety, Commins says.
How Is the Alpha-Gal Syndrome Allergy Treated?
There is no treatment for AGS other than changing your diet. If the diagnostic test comes back positive, you should should start an alpha-gal elimination diet and symptoms should resolve or significantly improve, says Lugar.
“The good news is that the allergy can resolve over a period of years if there are no additional bites,” says Commins.
Tick Bite Prevention Reduces Your Chance of Developing AGS
Preventing tick bites is important in preventing tick-borne disease and can reduce your chances of developing alpha-gal syndrome, according to the CDC.
The lone star tick is found throughout the eastern United States, and is more common in the South, according to the CDC. The greatest risk of being bitten by these “very aggressive” ticks is early spring through late fall.
At barely a quarter of an inch in diameter, the ticks are so small that you may not feel them on you or even notice if you’ve been bitten by one, per Emory University.
The CDC offers the following advice on avoiding tick bites and what to do if you find a tick on your clothes or body.
Be aware. You’re more likely to encounter ticks on a camping trip or hike through the woods, but many people get ticks in their own backyard, especially if they live in grassy, brushy, or wooded areas.
Treat clothing with tick repellent. Products containing 0.5 percent permethrin can be used to treat boots, clothing, and camping gear; the protection can last through several wash cycles.
Use insect repellent. The Environmental Protection Agency (EPA) has a search tool to help you find the safest and most effective insect repellent that suits your needs.
Check your clothes, gear, and pets for ticks after you come inside. If you find a tick on your clothing, remove it and dry your clothes in a dryer on high heat for 10 minutes. If your clothes need to be washed first, wash them in hot water to kill the ticks.
Check your body. After you’ve been outdoors, do a full body check including under the arms, in and around the ears, inside the belly button, behind the knees, in and around your hair, between the legs, and around the waist.
If you do find a tick on your body, don’t pull it off with your fingers. The CDC offers a step-by-step guide on how to safely remove a tick from your skin, how to dispose of it, and what to do if you develop a rash or fever within several weeks of removing the tick.
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