February 19, 2019
Can a Tick Bite Lead to Food Allergy?
Ask the Experts

Can a Tick Bite Lead to Food Allergy?

by Wellness Letter  

Q: Is it true that getting bitten by a certain type of tick can cause a person to become allergic to red meat?

A: Yes. Recently there have been reports of people who had been bitten by lone star ticks (named for the white marking on the arachnid’s back that resembles a star) or possibly some other species of ticks, and then developed allergic reactions after eating red meat (notably beef, pork, and lamb). The reactions involve itchy skin, hives, diarrhea, and vomiting, as well as potentially life-threatening anaphylaxis, characterized by impaired breathing and a drop in blood pressure.

The culprit for this allergic reaction is a carbohydrate found in red meat commonly called alpha-gal (gal is short for galactose, a type of sugar). It’s not entirely clear how a tick bite leads to this allergic reaction.

One likely scenario is that a tick picks up alpha-gal after biting an animal and then transfers it via its saliva to a human it bites, thus sensitizing the person. Or a bacterium carried by the ticks may play a role. Some allergic individuals can develop the reactions even after consuming milk or butter. There’s preliminary evidence that chiggers (also called red bugs or harvest mites) may also cause alpha-gal sensitization.

It’s unusual for a food allergy to be caused by a carbohydrate; most are caused by proteins. It’s also unusual that the symptoms typically develop three to six hours after eating red meat; most allergic reactions to foods occur within 30 minutes or so. This delay can make the condition difficult to diagnose.

Cases of tick-related meat allergy, once considered rare, have become more common in recent years, perhaps because of the rising populations of lone star and other ticks, thanks to warming temperatures and more abundant host animals. Once found primarily in the Southeast, lone star ticks are now also found in the Northeast and Midwest. Alpha-gal allergy also occurs in some other countries, where different species of ticks are involved.

Even if you don’t remember being bitten by a tick, if you’ve had an allergic reaction several hours after eating red meat, consult your doctor, who may refer you to an allergy specialist. The allergy can be diagnosed by a blood test. It’s not known if the allergy lasts a lifetime or lessens over time.

Clearly, you should avoid red meat if you have had a severe gastrointestinal or anaphylactic reaction after eating it.

This article first appeared in the UC Berkeley Wellness Letter.

Also see Vector-Borne Illnesses on the Rise.