A close-up of a lone star tick, and an image of ground beef.

Most of us worry about Lyme disease or Rocky Mountain spotted fever when getting a tick bite. But different species of ticks can transmit a variety of diseases—and at least one very unusual ailment, scientists have learned: an allergy to red meat.

A growing body of evidence shows that the lone star tick—most prevalent in the southeastern U.S.—could be the cause of an allergy to a carbohydrate known as alpha-gal, which is found in red meat.

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Scientists aren’t sure just how common this allergy is. 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.

2018 study in the Annals of Allergy, Asthma & Immunology suggests that a meat allergy caused by ticks may be more common than previously known, and could explain some previously unexplained cases of severe allergic reactions.

Here’s what you need to know about this allergy.

What Recent Research Reveals

Initially, scientists connected the dots between lone star ticks and meat allergies because of overlap between the geographic areas where the tick and the allergy were most common, according to an analysis published earlier this year in Annals of Allergy, Asthma & Immunology. Other studies showed that people who had the allergy tended to have a history of being bitten by ticks, or worked in jobs where they were likely to be exposed to ticks.

And in two recent cases reported in The Journal of Allergy and Clinical Immunology: In Practice, people who had an allergic reaction to red meat developed hives around the area where they had been previously bitten by a tick.

The 2018 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 between 2006 and 2016. That’s more than were caused by food allergies to peanuts, shellfish, or others, the researchers found.

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 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 newer study suggests that a significant number of those earlier cases with an unknown cause may actually have been due to this recently discovered allergy.

Understanding Meat Allergies

It’s not entirely clear to scientists why a bite from a tick could 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.

What to Watch For

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, talk to your doctor about whether red meat could have been the cause of your symptoms, since some doctors may not be aware of the alpha-gal allergy, suggests Princess Ogbogu, M.D., division director of allergy and immunology at The Ohio State University Wexner Medical Center.

There’s no cure for red meat allergy, so if you’re diagnosed, you’ll need to avoid the foods that trigger a reaction. Commonly, that includes various kinds of red meats. But some people can also become sensitive to other items that contain alpha-gal, including dairy, and even, rarely, sweets that contain gelatin or medications derived from animal byproducts.

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

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 likely 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 products containing 25 to 30 percent deet provide the most reliable protection. (Check out our top-rated repellents.)

Dress carefully. Wear long pants and long sleeves, and tuck your pants into your socks. Wearing clothing commercially treated with the pesticide permethrin, or treating your clothes and gear with permethrin yourself, is also a good option for additional protection.

Check yourself for ticks at the end of every day you’ve been out in their territory. Taking a shower soon after you come in is a good opportunity to wash away any ticks that may be crawling on your skin without having yet bitten you, and to carefully look for any that have attached. If you find them on you, remove them properly.

Be careful with the clothes you were wearing in tick habitats, Stromdahl recommends. 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.