Ticks are annoying creatures. These nasty, bloodsucking parasites glom on to you when you least expect 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 bizarre and sometimes dangerous allergies 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 report from the Centers for Disease Control and Prevention. But researchers think there might be closer to half a million people living with the condition—and the number of cases is increasing.
Many health-care providers still don't know about alpha-gal syndrome at all. A 2022 CDC survey found that 42 percent of them had never heard of the condition, and more than a third of those who were aware of it were not confident in diagnosing or managing the allergy. If people with the syndrome consume animals or products containing 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.
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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 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 animals, including 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 earlier in the day, and it's also difficult to associate them with tick bites that might have happened weeks or months before any of the symptoms started. All these factors make the syndrome difficult to recognize and diagnose.
And 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 both among the public and among health-care providers so 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 those mammalian meats have the alpha-gal sugar.
Is it a lifelong allergy?
In some patients, the antibodies responsible for the reaction will decline over time. Some patients have reported success in adding back mammalian products over a few years. But for others, 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 most of the testing for alpha-gal-specific antibodies in the U.S., and it was willing to share its data with us. Looking at those data, we could estimate that over the past 12 years there were at least 110,000 “suspected” cases of alpha-gal—that means they had a positive lab result, but we didn't have other information about those patients. Given the lack of awareness among health-care providers, however, we suspect that 110,000 is quite a bit of an undercount, and we estimate as many as 450,000 people may be living with the syndrome in the U.S. And the number of positive tests has been going up year by year.
Where are most of the cases occurring?
The majority of cases are in a region starting in Missouri and Arkansas, going east through Tennessee, Kentucky, Virginia and North Carolina, and then stretching up the Eastern Seaboard a little bit. This pattern overlaps what we expect the distribution of the lone star tick to be. We think this tick is the one responsible for most cases in the U.S. In fact, 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 we also 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 remove any ticks that you find as soon as possible. We're not certain how long the tick has 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 repellents, 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. 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 if you have alpha-gal syndrome, it's important to talk to your health-care provider when you're considering a vaccine. Most vaccines do not cause this problem. 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 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?
Yes, 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 and infectious tickborne diseases. That is something to think about when a patient comes in and it's unclear what their diagnosis is.