New study reveals how a tick bite can cause a red meat allergy

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It does not take more than a single bite from a lone star tick that can spark a life-long allergy to red meat. This bizarre side effect has long been shrouded in mystery and misunderstanding, but a new study has taken a bold nudge forward in understanding the underlying mechanism that allows a humble tick to turn a BBQ-loving carnivore into a dedicated vegetarian.

The lone star tick, aka the northeastern water tick or the turkey tick, can be found across much of the eastern United States and Mexico. This aggressive tick needs to feed on the blood of humans, white-tailed deer, small mammals, and wild turkeys, in order to complete each stage of its life cycle.

The ticks bite is typically painless and often goes unnoticed, however, it occasionally leaves the host with a bacterial infection known as ehrlichiosis. In some unfortunate cases, it can also spark an alpha-gal allergy, whereby the immune system reacts to alpha-gal, a carbohydrate found in most mammalian cell membranes. This means the person can no longer eat beef, dairy, pork, and lamb, although they can eat chicken and fish (and primate meat, for that matter) with no problem.

This is not your typical food allergy, however. For one, people can often test negative for meat allergies during standard allergy evaluations. People often have delayed onset of symptoms such as the constriction of airways and a drop in blood pressure, occurring three to 8 hours after consuming the meat.

In the U.S., the Lone Star tick has expanded its range beyond the Southeast, and there are documented cases of alpha gal meat allergies farther north — including New York, Maine and Minnesota.

Dr. Scott Commins, an allergist and associate professor of medicine at the University of North Carolina, Chapel Hill. He says it is a meat allergy, but about 15 to 20 percent of patients with the alpha-gal allergy also report getting symptoms from dairy, especially high-fat dairy such as ice cream.

About 10 years ago, Commins was among the first physicians to identify the allergy in patients with tick bites. Back then, there were just a few dozen known cases.

That has increased dramatically. “We’re confident the number is over 5,000 [cases], and that’s in the U.S. alone,” Commins says. There are also cases in Sweden, Germany and Australia — likely linked to other species of ticks.

“The range of the tick is expanding,” says Commins. So is awareness about the red meat allergy it can cause. “We have a blood test, and the word is getting out.”

Commins first began trying to solve the mystery of what was causing a red meat allergy in 2007, when he was at a University of Virginia allergy clinic. “We had a growing population of people reporting these reactions [to meat],” he recalls.

Early on, ticks were not on his radar. “We thought it was a parasite,” Commins explains. But then he and his colleagues realized that many of the patients were outdoorsy types who spent time hiking. And eventually they pieced together the tick bite connection.

One hint came from mapping newfound cases of the meat allergy. When he compared that with the geographic distribution of Rocky Mountain spotted fever, also caused by the Lone Star tick, he saw striking similarities. “That map overlapped very nicely with the states where we were finding these emerging reactions to beef, pork and lamb,” he says.

There’s still a lot to learn about the alpha-gal allergy. Alpha gal is a sugar that animals — including cows, pigs and lamb — make in their bodies. “As humans, we don’t make this alpha gal sugar,” Commins explains. “We all make an immune response to it.” So, how does a tick bite cause the allergy?

It’s possible that ticks inject humans with alpha gal when they bite. The ticks likely get it from feeding off wild animals, such as mice or squirrels, that also carry alpha gal. Or it’s possible that ticks activate the response in another way.

Reporting in The Journal of Immunology, scientists at the University of Virginia School of Medicine set out to find the key immunological changes in people who experience this unusual allergic reaction.

“We don’t know what it is about the tick bite that causes the meat allergy. And, in particular, we haven’t really understood the source of immune cells that produce the antibodies that cause the allergic reactions,” study author Loren Erickson explained in a statement.

Many questions remain. For one, it’s unclear how a superficial skin bite can lead to a loss of tolerance to alpha-gal in the gut. It also isn’t understood why the meat allergy only emerges in some patients but not others.

However, armed with this knowledge about the B cells, the researchers hope they’re a step closer to understanding this curious affliction and perhaps nearing a viable treatment for it.

“This is the first clinically relevant model that I know of, so now we can go and ask a lot of these important questions,” Erickson concluded. “We can actually use this model to identify underlying causes of the meat allergy that may inform human studies.”