Alpha-gal Syndrome: How to Spot Symptoms of This ‘Red Meat Allergy’
Most people who are bitten by a tick know to look out for the telltale bull’s-eye rash that can indicate Lyme disease.
But there is another tick-borne condition—alpha-gal syndrome (AGS)—that has no such visible clue and causes an allergy to red meat and other products derived from mammals.
Alpha-gal, which is short for galactose-a-1,3-galactose, is a sugar molecule found in all mammals except for humans and primates. Certain ticks, primarily the lone star tick, can carry alpha-gal (in their saliva or stomach) and transmit the molecule to people by biting them.
In some people, alpha-gal triggers a reaction in their immune system that causes an allergic response whenever they eat red meat, including beef, pork, or lamb, or when they use medications (more on this below) or food products derived from mammals, such as milk and gelatin. The Centers for Disease Control and Prevention (CDC) provides a list of foods and products that contain alpha-gal.
The allergic reaction typically occurs hours after ingesting the food or product and symptoms can range from mild—such as hives or a rash—to life-threatening—in the form of anaphylactic shock, which causes a sudden drop in blood pressure, airway constriction, and difficulty breathing.
“We usually think about food allergy as you eat a food and then within a half hour or maybe an hour, you have a reaction,” says Ryan Steele, DO, a Yale Medicine allergist-immunologist. “With alpha-gal, that is delayed, so a lot of these cases went unrecognized for years.”
How common is alpha-gal syndrome?
AGS was first identified in the early 2000s in the United States, and although it is considered rare, the number of cases increased between 2010 and 2022, during which time more than 110,000 suspected cases were identified, according to a 2023 report from the CDC. But the agency estimates that as many as 450,000 people may have been affected by AGS as of 2023, the most recent year for which official data is available.
Most cases from the CDC report occurred in southern, mid-Atlantic, and midwestern states (where the lone star tick is common), but suspected AGS cases also have been identified in areas outside this tick’s typical habitat—possibly due to such factors as climate change. “Other species, including chiggers, have also been potentially implicated in transmission, but this is currently under investigation,” Dr. Steele adds.
Much remains unknown about AGS, including why some people develop the condition and others don’t. Since it’s a food allergy, it differs from other tick-borne illnesses such as Lyme disease, which is a bacterial infection transmitted by ticks, leading to symptoms such as fever, fatigue, rash, and joint pain.
What are the symptoms of alpha-gal syndrome?
When someone has a food allergy, a reaction typically occurs soon after eating the offending food.
“But alpha-gal has the nickname of ‘midnight anaphylaxis’ because people who eat foods containing alpha-gal often wake up in the middle of the night with symptoms,” Dr. Steele says, adding that those symptoms can include hives, nausea, heartburn, diarrhea, shortness of breath—or, as noted earlier, anaphylactic shock, an extreme reaction that would require injectable epinephrine (EpiPen), followed by medical evaluation.
Additionally, alpha-gal can be found in many medications derived from mammals, including cetuximab (a chemotherapy drug) and certain thyroid hormone supplements (levothyroxine, among others). Unlike food reactions, if someone has AGS and takes an intravenous medication that contains alpha-gal, the allergic reaction can be immediate. Alpha-gal can also be found in medical products, including gel capsules and prosthetic heart valves from cows or pigs.
While some people have a genetic predisposition to developing allergic conditions, Dr. Steele says that AGS can occur in those who don’t have allergies, including seasonal or food allergies.
It’s unclear how long it takes for a person who has been bitten by a tick with alpha-gal to mount an allergic response. The more times a person is bitten and exposed to alpha-gal, the more likely they are to have an allergic reaction, Dr. Steele says.
“There is still a lot of research that needs to be done around alpha-gal,” he says.
How is alpha-gal diagnosed and treated?
“Fortunately, we have a way to test for alpha-gal syndrome,” Dr. Steele says. “We can do a blood test to measure levels of antibodies, specifically of immunoglobulin E, or IgE, to the allergen. We can track the levels over time and see if they get low enough for potentially reintroducing beef into someone’s diet.”
Symptoms can be managed by not consuming products made from mammals and by using antihistamines to manage mild allergic reactions. As a precaution, Dr. Steele recommends his patients with AGS also carry epinephrine to treat more severe reactions.
“People should monitor themselves for signs of an allergic reaction and an anaphylaxis plan should be worked out with their health care provider to guide on medication use,” Dr. Steele says.
Before reintroducing red meat or other products that cause an allergic reaction into someone’s diet, Dr. Steele says he usually waits until a blood test shows reduced levels of alpha-gal. If appropriate, a food challenge may be offered. This involves coming into the office and eating foods containing alpha-gal.
“We carefully watch them as we increase the doses, and we take their vital signs and make sure they’re not having an allergic reaction,” Dr. Steele explains.
Dr. Steele says he has treated several patients with AGS who are now successfully eating meat again and other products that contain alpha-gal. “There’s no hard-and-fast timeline as this is a process, but IgE levels can drop over a period of months to years,” he says.
Meanwhile, the best way to prevent AGS is to avoid tick bites, including by wearing tick repellent that contains picaridin, DEET, or oil of lemon eucalyptus when outdoors, especially if you are in wooded areas or in high grass. Also be sure to carefully check your body when you come back inside. If you find a tick attached to your skin, remove it carefully with tweezers and see your doctor if you develop a rash, fever, or allergic symptoms.
