Q&A with allergist Scott Commins, MD, PhD, on the fascinating link between tick bites and developing an allergy to meat.
Allergist Scott Commins, MD, PhD, is one of the nation’s leading experts on the alpha-gal allergy, an allergy to mammal meat induced by a tick bite. A member of the University of Virginia’s research team that discovered alpha-gal allergy about ten years ago, Commins now heads the laboratory that studies the allergy at the University of North Carolina. He also serves as Associate Professor of Medicine in the Division of Rheumatology, Allergy and Immunology and has a clinical practice that specializes in diagnosing and treating patients with the alpha-gal allergy.
GF&M: What is the alpha-gal allergy? Can you comment on its oddball aspects?
Dr. Commins: The alpha-gal allergy is a reaction to a carbohydrate in mammal meat—beef, pork, lamb, venison and others. In many ways, it has totally changed the paradigm of food allergy. Other food allergies are a reaction to protein, not a carbohydrate. The alpha-gal allergy results from tick bites or other insect bites, which is a first for a food allergy. It’s unusual for adults to develop an IgE response to a food that they have tolerated their entire lives, yet the alpha-gal allergy occurs at any age. Food allergy reactions typically happen within 30 minutes of ingesting the allergen, two hours at the most. With the alpha-gal allergy, the reaction is delayed. You eat meat for dinner and you wake up with gastrointestinal symptoms later that night, four to six hours later.
GF&M: Typical symptoms are gastrointestinal? Any itching or hives?
Dr. Commins: Some people allergic to alpha-gal report significant GI symptoms. However, many people report GI symptoms as part of a constellation of symptoms that includes itching, hives, swelling, lightheadedness and even shortness of breath. We do know that alpha-gal allergy can produce a GI-only reaction that doesn’t necessarily come with any other manifestation or symptoms. I also want to make the point that food allergy does not always present with hives, itching or swelling. We’re probably missing people who get bad abdominal pain or GI cramping four to six hours after eating a hamburger. Many never come to the attention of an allergist.
GF&M: How does an allergist make an alpha-gal allergy diagnosis?
Dr. Commins: Patients with a clinical history consistent with the alpha-gal allergic reaction undergo an alpha 1, 3 galactose IgE blood test. Any result over .35 is considered positive for the allergy.
GF&M: Is this allergy becoming more prevalent?
Dr. Commins: I feel like incidence is on the rise. I can’t quote you the rate from, say, 15 years ago because we didn’t have a test to detect this allergy then. But anecdotally, I see these patients a lot. On any given day in clinic, I might see four or five patients with a brand new meat allergy.
GF&M: What kind of tick causes the alpha-gal allergy?
Dr. Commins: It’s not just the lone star tick, which is what we used to think. This allergy has been described in Australia, Europe, South America and Central America where there are different ticks. We’re currently having discussions with a collaborator in Cape Town, South Africa, who has over 80 patients with this allergy and only two or three of them report a tick bite. His thinking is that different ectoparasites, such as mosquitos and others, are involved. In the United States, particularly in the South and East, ticks are indicated in the alpha-gal allergy but I’m not convinced that’s the only answer globally.
GF&M: How long does the tick have to be attached to be a problem?
Dr. Commins: We’ve seen some established patients who get an additional tick bite. They feel the tick crawling on them, it bites them very quickly and they get it off almost instantaneously—but their alpha-gal IgE levels still increase.
GF&M: What if you have a raised IgE level but you don’t have a reaction to eating meat? Does that mean you’re not necessarily allergic?
Dr. Commins: This is one of the great questions in all of food allergy at the moment: What is the positive predictive value of an IgE-positive test? And the answer is that it has to fit with the clinical history. If we take 100 kids and test them all for peanut IgE, about a dozen will be positive and of those 12, probably two will actually have an allergic reaction. So people can have a detectable IgE against a food allergen but not be clinically allergic.
Not everyone who has the alpha-gal IgE necessarily has a clinical reaction. We looked at a group of around 50 park rangers in North Carolina and found that nearly 80 percent of them had some IgE detectable to alpha-gal, yet only a handful had a reaction to eating red meat. If you’re out there getting tick bites, you may develop the alpha-gal IgE but it may not necessarily cause a clinical reaction.
GF&M: So someone who has IgE-positive antibodies but never had an allergic reaction can eat meat and not worry?
Dr. Commins: It’s a nuanced answer—but the upshot is that in a setting where you have positive alpha-gal IgE results but there’s no clear history of reactions, you should undergo a medically supervised food challenge. With alpha-gal allergy, the presence of alcohol or exercise seems to facilitate a reaction. Often if a patient successfully completes a traditional challenge—they eat pork sausage, sit and wait in our clinic for hours and nothing happens—then we follow that with a challenge where every 30 minutes they walk the stairs.
GF&M: Is it possible for somebody to react to only a certain type of meat, like beef but not lamb?
Dr. Commins: Animals express the alpha-gal sugar in their tissues in different amounts. For instance, pork kidney, a food eaten by Europeans, has the highest concentration of alpha-gal of any tissues we’ve examined. Fat content is also a factor. A patient might react to a fatty hamburger but not to lamb that’s more cooked and so contains less fat.
GF&M: So mammal meat with more fat induces more of a reaction. What’s the link to fat?
Dr. Commins: The issue with fat is that the alpha-gal on the fat molecule appears to be protected in some way so that it doesn’t get digested. In our mouse model, the fat alone (without the meat) created these reactions. It comes down to the specific biology of fat absorption. It appears that the alpha-gal present in fat does not get digested in the early phase like so many sugars do. We’ve shown this in our lab using a mouse model and pork fat.
GF&M: Your research suggests that some people with this allergy may also develop an allergy to dogs or cats.
Dr. Commins: Yes. The dander of mammals—cats, dogs, horses, goats or whatever—contains alpha-gal. We’ve found that some patients are fairly sensitive to this. If they spend a lot of face time with their pet, they report some itching or maybe some heartburn that could possibly be attributed to the animal’s dander.
GF&M: Some people seem to react to dairy and some people don’t.
Dr. Commins: Yes. There are clearly different sensitivities among patients. Some folks are really sensitive and they’re bothered by dairy. Other patients are not.
GF&M: Does the amount of meat matter?
Dr. Commins: For most people, it does seem to be dose-dependent. Some folks can eat a piece of bacon but they can’t eat a BLT. We’re trying to figure out whether this has to do with the absorption of fat or whether there truly are endogenous differences in antigen presentation and processing for various individuals.
GF&M: Is the alpha-gal allergy a permanent condition or are people able to overcome it if they avoid additional tick bites?
Dr. Commins: It appears the alpha-gal IgE wanes over time. We have patients with the allergy who are able to avoid ticks or other bug bites for some time and their IgE goes away. They undergo a successful food challenge in the clinic and a successful exercise challenge—and they are clear to go.
GF&M: Are there indications that alpha-gal allergy might be more permanent for one person than another?
Dr. Commins: I haven’t seen any indication it might be more permanent for any one person. But if you have a history of ongoing tick bites—for instance, you work on the railroad and you’re constantly in brush and long grass—it seems very unlikely that you will be able to become clear of the alpha-gal IgE.
GF&M: There are still so many unanswered questions about alpha-gal allergy. What kinds of things are you investigating?
Dr. Commins: My lab is focused on several areas of interest. One is, what in the world is going on with a tick bite? How do we explain why some ticks cause alpha-gal allergy and others don’t and why some people get alpha-gal allergy and others don’t?
We’re trying to understand if multiple tick bites might alter our basophils. In other words, can repeated tick exposure cause an epigenetic change that increases susceptibility to the alpha-gal allergy?
We’re also investigating the physiology of exercise and its relationship to food absorption and food allergy. This goes beyond the alpha-gal allergy. Almost 100 percent of the children who tragically died from food-allergic reactions were involved in some kind of physical activity—dancing, running, playing on the playground. Exercise is involved in bad outcome. We’re really interested in understanding what it is that exercise does and how we can prevent that, not only for patients with alpha-gal allergy but for everyone with food allergy.
Alicia Woodward is editor-in-chief of Gluten Free & More magazine.