How a Tick Bite Can Make You Allergic to Meat
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Most of us worry about Lyme disease or Rocky Mountain spotted fever when getting a tick bite. But now scientists say tick bites could give you an allergy to red meat.
That's because the lone star tick—most prevalent in the southeastern U.S.—has been shown to cause an allergy to a carbohydrate known as alpha-gal, which is found in red meat.
A new study in the Annals of Allergy, Asthma & Immunology suggests that a meat allergy caused by ticks may be more common than previously known, and that this tick-induced allergy could explain some previously unexplained cases of severe allergic reactions.
The study looked at just one allergy clinic in Tennessee, and found that in cases where they were able to pinpoint the cause, the alpha-gal allergy was behind about a third of anaphylaxis (severe allergic reaction) cases seen there, making it the most common known cause of reactions they treated.
Study author Jay Lieberman, M.D., associate professor at the University of Tennessee Health Science Center and vice chair of the American College of Allergy, Asthma and Immunology Food Allergy Committee, is quick to point out that these results do not mean that a third of severe allergic reactions nationwide are due to the effects of lone star tick bites, or that alpha-gal is the number one cause of anaphylaxis in the country.
But lone star ticks are spreading—their habitat now extends from the Southeast almost all the way to the Canadian border—which means more people may encounter them. Scientists who study the alpha-gal allergy estimated back in 2013 that more than 5,000 people in the Southeast U.S. alone could have the allergy.
And Princess Ogbogu, M.D., division director of allergy and immunology at The Ohio State University Wexner Medical Center (who wasn’t involved with the new study), says that from what she’s seen in her practice, plenty of these allergies have likely gone undiagnosed—in part due to a lack of awareness about the allergy among patients and even many doctors.
So just how concerned should you be about this allergy, which, in the U.S., is only caused by the bite of a lone star tick? We spoke with the study authors and other experts to find out.
What the Study Found
In the new study, researchers with the University of Tennessee Health Science Center evaluated cases of anaphylaxis they’d handled between 2006 and 2016. They found 218 cases that met the definition of anaphylaxis—a constellation of symptoms that can include hives, swelling of the tongue and lips, trouble breathing, wheezing, abdominal cramping, vomiting, and low blood pressure.
Researchers performed allergy testing and evaluated people's medical histories to determine the cause of the reaction, which they were able to do with reasonable certainty in 85 of the 218 cases.
Of those 85 cases, 28—or about 33 percent—were found to have been caused by the tick-bite-induced allergy to red meat. That’s more than were found to be caused by food allergies to peanuts, shellfish, or others.
Lieberman says the clinic has performed similar analyses in previous years, before the alpha-gal red meat allergy was discovered. In those earlier studies, doctors weren’t able to determine a cause for a greater percentage of anaphylaxis cases.
The data from the new study suggest that a significant number of those earlier cases with an unknown cause may actually have been due to this newly discovered allergy.
Understanding Meat Allergies
It’s not entirely clear to scientists why a bite from a tick can cause a person to develop an allergy to red meat, Lieberman says, or how common such an allergy is. And it doesn’t happen to everybody who’s bitten.
Only some people who’ve been bitten by lone star ticks will develop the antibodies that indicate a possible allergy to alpha-gal, a substance in red meat. Of the people who do develop those antibodies, Lieberman says, some won’t ever show symptoms of an allergic reaction to red meat.
There’s also an intriguing difference between the alpha-gal red meat allergy and every other type of food allergy. Typically, allergic reactions to food occur immediately after exposure, within a few minutes. With an alpha-gal allergy, however, a reaction typically doesn’t start until several hours after eating red meat—which can make it challenging to pinpoint the culprit.
Researchers first linked tick bites to red meat allergies almost a decade ago. But there are still a lot of questions left to answer about why some people develop the allergy and some don’t, how many people have been affected, and why the reaction to red meat is delayed, rather than immediate.
Early signs of anaphylaxis may include a metallic taste, burning, tingling, or itching of the tongue or mouth, headache, and feelings of fear or confusion. A reaction can progress quickly, and severe symptoms include throat swelling, difficulty breathing, vomiting, diarrhea, and more.
If you think you may be experiencing anaphylaxis, even if you’ve never had an allergic reaction before, you should call 911. (If you know you have an allergy to food, and you experience symptoms of anaphylaxis, especially trouble breathing, wheezing, or throat swelling, you should use an epinephrine auto-injector if you have one.)
When the reaction is under control, Ogbogu recommends patients ask their doctors whether red meat could have been the cause of their symptoms, since some may not be aware of the alpha-gal allergy.
There’s no cure for red meat allergy, so if you’re diagnosed, you’ll need to avoid the foods that trigger a reaction. That could include various kinds of red meats, and even sometimes milk (which also contains alpha-gal), according to UpToDate, an online decision-making tool for doctors.
In some cases, Lieberman says, if people who’ve developed alpha-gal allergies avoid all future tick bites from lone star ticks (or the varieties that cause the allergy in other countries), their levels of the antibodies to alpha-gal may diminish, and the allergy could subside. It’s unknown how common this is, however.
About the Lone Star Tick
The clinic in this study is located in Tennessee—which is right in the heart of lone star tick territory. (Lieberman notes that this may be one reason his clinic has seen so many red meat allergies, and that other areas of the country would likely see different numbers.)
Lone star ticks, so named for the white splotch on the backs of adult females, are most common in southern and eastern states. Like other ticks, however, their geographic distribution is expanding, according to Ellen Stromdahl, a retired entomologist from the tickborne disease laboratory of the U.S. Army Public Health Center in Aberdeen Proving Ground, Md.
Lone star ticks don’t cause Lyme disease, as a recent analysis that Stromdahl conducted shows. But along with spreading the alpha-gal allergy, they can also transmit the bacteria that cause another disease called ehrlichiosis. Ehrlichiosis can cause fever, muscle pain, nausea, vomiting, and, rarely, rash. It’s fatal in about 1.8 percent of cases, according to the Centers for Disease Control and Prevention, although it can be treated with antibiotics.
A lone star tick is much less likely to carry ehrlichiosis than a blacklegged tick is to carry Lyme disease, notes Stromdahl. But lone star ticks are much more aggressive than other common types of ticks in the U.S. “You’re more likely to be mobbed by lone star ticks,” she says, and finding multiple bites is common if you’ve been in their habitat.
Protect Yourself From Ticks
As with any tick bite, it’s important not to panic if you discover one, Lieberman says. “The vast majority in this country and elsewhere who get bitten by ticks don’t develop alpha-gal allergy,” he says.
Still, you can take reasonable precautions to protect yourself from ticks and the diseases—or allergies—they can cause. Here’s what to do:
Wear an effective bug spray if you’re going to be in an area where ticks are common. Lone star and other types of ticks prefer wooded areas, brush, and long grass. Consumer Reports’ insect repellent testing has found that some products containing 15 to 30 percent deet, 20 percent picaridin, or 30 percent oil of lemon eucalyptus can provide the best protection.
Dress for the occasion. Wear long pants and long sleeves, and tuck your pants into your socks. Stromdahl also suggests using permethrin-treated clothing for additional protection.
Keep your yard unfriendly to ticks. Keep your lawn grass cut, since ticks love tall grasses. Clean up brush and weeds, too. Find more tips on tick-proofing your yard here.
Check yourself for ticks at the end of every day you’ve been out in their territory. If you find them on you, remove them properly. And Stromdahl recommends taking care with the clothes you were wearing. Run them through a cycle in a hot dryer to kill any ticks that may be clinging on, and leave your shoes outside in the sun.
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