Ticks are annoying creatures. These nasty, bloodsucking parasites glom on to you when you least suspect it. And if they’re not removed in time, they can transmit a startling range of pretty horrible diseases.

The bite of the lone star tick, found in the U.S. South, Midwest and mid-Atlantic, can trigger a bizarre and sometimes dangerous allergy to red meat (such as beef, pork and venison), dairy, gelatin and some medications. Known as alpha-gal syndrome, the condition is caused by an immune reaction to the sugar alpha-gal (galactose-α-1,3-galactose), which is found in the flesh of most nonprimate mammals. More than 110,000 people in the U.S. tested positive for alpha-gal antibodies from 2010 to 2022, according to a July 28 report from the Centers for Disease Control and Prevention. But researchers think the actual number of people living with the condition may be closer to half a million—and cases are increasing.

Yet many health care providers don’t know about alpha-gal syndrome at all. A 2022 CDC survey, also reported on July 28, 2023, found that 42 percent of them had never heard of the condition. And  more than a third of those who were aware of alpha-gal syndrome were not confident in diagnosing or managing it. If people with the syndrome consume animals or products with alpha-gal sugar, they can suffer reactions ranging from diarrhea to hives to anaphylactic shock. There is no treatment, and many patients are forced to radically alter their diet for years—or for life.

A Blacksburg, Va.–based company called Revivicor raises pigs that are genetically engineered to lack the alpha-gal gene with the aim of growing organs that can be transplanted into humans. The U.S. Food and Drug Administration approved these “GalSafe” pigs in 2020 for meat as well as medical use (though not specifically for transplants). Revivicor occasionally provides GalSafe pork to people with an alpha-gal allergy, but it does not sell the meat. “We try whenever possible to make GalSafe meat available to alpha-gal patients, but we are not meat producers,” says Dewey Steadman, head of investor relations at Revivicor’s parent company United Therapeutics. “We’ve been unsuccessful in our efforts to find a partner to produce GalSafe meat on a larger scale.” The company is focused more on manufacturing organs, he adds.

Scientific American talked to Gilbert Kersh, one of the authors of the July 28 CDC reports and chief of the Rickettsial Zoonoses Branch at the CDC’s Division of Vector-Borne Diseases, about what alpha-gal syndrome is and what doctors and the public should know about it.

[An edited transcript of the interview follows.]

What causes alpha-gal syndrome?

Alpha-gal syndrome is a tick-bite-associated allergic condition. We think people, a few weeks or maybe a couple of months after getting a tick bite, start having allergic reactions when they consume red meat or other products that contain the alpha-gal sugar. Alpha-gal is a sugar that is in most mammalian meat. But it’s not present in humans, so humans [with the condition] recognize it as foreign and have a reaction to it. These reactions take place when people are exposed to mammalian meat or other products derived from meat; this includes dairy products for many patients. These reactions will come two to six hours after they consume the meat or other product.

What are the most common symptoms?

There’s a group of patients who report primarily gastrointestinal symptoms, so they’ll have diarrhea or vomiting. Often this will come late at night because they’ve had an evening meal that included red meat. And there are other patients who have more traditional allergic reactions—who will have hives—and some develop anaphylaxis. They may have trouble breathing, swelling of the tongue, those kinds of symptoms—which can be quite serious and often result in visits to the emergency department. It’s often difficult to tie these reactions to the consumption of meat that may have happened earlier in the day, and it’s also difficult to associate it with tick bites that might have happened weeks or months before all of this started. All these factors make it difficult to recognize and diagnose.

Do doctors know how to diagnose the condition?

We did a survey of health care providers, and 42 percent of them had not heard of alpha-gal. An additional 35 percent were not too confident in their ability to diagnose or manage a patient who had it. We think there’s really a gap in awareness among health care providers about recognizing these symptoms and the sequence of events that leads to alpha-gal syndrome. One of our objectives is to increase awareness about alpha-gal syndrome, both among the public and among health care providers, so that it can be recognized and managed appropriately.

Is there a treatment for the condition?

There’s no treatment or cure for alpha-gal syndrome, but patients can manage the condition by avoiding eating things that have the alpha-gal sugar. You can use chicken or fish as a protein source but not pork or venison or beef—all of those mammalian meats have the alpha-gal sugar.

Is it a lifelong allergy?

In some patients, the antibodies that are responsible for the reaction will decline over time. Some patients have reported success in adding back mammalian products over a few years. But for some patients, it’s a lifelong condition.

Is alpha-gal syndrome widespread?

Yes, and it is increasing as well. There is no formal national surveillance for alpha-gal syndrome. In the recent article [on cases of alpha-gal syndrome] that we published in [the CDC’s] Morbidity and Mortality Weekly Report, we used kind of a proxy for formal surveillance. There was a laboratory that did the majority of testing for alpha-gal-specific antibodies in the U.S., and they were willing to share their data with us. Looking at that data, we could estimate over the past 12 years, there were at least 110,000 “suspected” cases of alpha-gal—that means they had a positive laboratory result, but we didn't have other information about those patients. With the lack of awareness among health care providers, however, we suspect that that 110,000 is quite a bit of an undercount, and 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. In 2021 there were more than 18,000 people with alpha-gal-antibody-positive test results.

Where are most of the cases occurring?

The majority of cases are in a region starting from Missouri and Arkansas, going east through Tennessee, Kentucky, Virginia, North Carolina and then stretching up the Eastern Seaboard a little bit. This pattern of distribution overlaps what we expect the pattern of the lone star tick to be. We think this is the tick that is responsible for the majority of cases in the U.S. Actually Suffolk County, New York, which is on Long Island, had the most positive test results of any county in the U.S. That’s a region that has a large number of lone star ticks, but also, we think there’s more awareness in that area, so people are getting diagnosed in a more timely manner there.

If you’re bitten by this tick, what can you do?

We recommend that anytime you go outdoors, you follow that up with checking for ticks and that you remove any ticks that you find as soon as possible. We’re not aware how long it takes the tick to be embedded for the alpha-gal antibodies to be introduced. So the safest thing to do is to remove a tick as soon as you find it. But it’s better if you don’t get bitten by the tick at all. Taking personal protective measures is really important for preventing alpha-gal syndrome: using Environmental Protection Agency–registered repellants, checking yourself for ticks when you return from outdoors, walking in the middle of a trail—those are tick bite preventions that are applicable to any tickborne disease.

But in this case, that’s really the only prevention we have for reducing cases of alpha-gal syndrome. It’s also an issue that once you have alpha-gal syndrome, subsequent tick bites can boost the alpha-gal antibodies. So if you want to be one of those people who, over time, improves and can tolerate some mammalian products, you really need to avoid any subsequent tick bites after you have it.

Do people with alpha-gal syndrome react to other things besides red meat and dairy products?

Patients report that it’s difficult to completely avoid all the products—the sugar is present in some pharmaceuticals such as gelatin-coated tablets. Marshmallows can contain mammalian products. There’s not a comprehensive list of what potentially might have mammalian products. This is the difficulty for patients, especially if they eat out: they don’t know exactly how the food’s been prepared or what’s in there. So it can be quite challenging for patients. But most report [that avoiding products with alpha-gal is] much better than the symptoms they were having when they were eating meat and having severe reactions.

It’s also possible to have a reaction to a vaccine. Those do not seem to be very common, but it’s important if you have alpha-gal syndrome to talk to your health care provider when you’re considering a vaccine. Most vaccines do not cause this. Definitely it’s not a reason to avoid getting vaccinated.

What should people with alpha-gal syndrome do if they ingest red meat or another product with alpha-gal?

Some patients, after they have these reactions, will carry an EpiPen. But once they get diagnosed, and they know what to avoid, typically there’s less of a risk of a severe reaction.

Tickborne diseases, including Lyme disease, are on the rise in general. Should health care providers be aware of these illnesses so they can diagnose patients?

Yeah, definitely. Over the past 25 years, we've seen a steady increase in basically all tickborne diseases, and a lot of new tickborne diseases have been identified in the past 20 years. So we would encourage awareness about all tickborne conditions—both alpha-gal syndrome plus infectious tickborne diseases—and that this is something to think about when the patients come in, and it’s unclear what the diagnosis is.