Unexplained cases of anaphylaxis linked to red meat allergy

A rare red meat allergy that starts after being bitten by a lone star tick may cause unexplained cases of recurrent anaphylaxis. Ribeirorocha/iStock/Thinkstock

Anaphylaxis is a life-threatening allergic reaction that can cause your airway to constrict and your blood pressure to drop dangerously low. Some people have repeated episodes of anaphylaxis for unknown reasons. Food allergies are a common cause of anaphylaxis; however, it’s not always easy to identify a food to which you’re allergic. Avoiding your allergy triggers is the best way to prevent anaphylaxis.

Researchers recently discovered a rare red meat allergy that starts after being bitten by a lone star tick. The allergy is to a sugar molecule called galactose-α-1,3-galactose, or alpha-gal, that’s found in beef, pork, lamb, and other red meats.

It’s difficult to identify this allergy because of its unusual time delay before symptoms appear. Allergic reactions to alpha-gal usually happen between 3 to 6 hours after eating red meat. In contrast, reactions to most common allergy-causing foods, like peanuts or shellfish, begin about 5 to 30 minutes after a person is exposed.

To investigate alpha-gal allergy as a possible cause for unexplained cases of recurrent anaphylaxis, a team led by Dr. Dean D. Metcalfe at NIH’s National Institute of Allergy and Infectious Diseases (NIAID) analyzed 70 patients who had been diagnosed with idiopathic anaphylaxis. Idiopathic means a cause couldn’t be identified. The research was supported by NIAID. Results were published in Allergy on November 21, 2017.

The researchers enrolled 46 females and 24 males between the ages of 15 and 70 years old. Six adult male participants had IgE antibodies—immune proteins associated with allergies—to alpha-gal in their blood. Each of the men had a history of tick bites and lived in states where lone star ticks reside. After implementing diets free of beef, pork, lamb, and venison, none of these participants experienced anaphylaxis for the period they were followed for the study (18 months to 3 years).

Among the six participants with the alpha-gal allergy, two also had a rare condition called indolent systemic mastocytosis, or ISM. People with ISM have an abnormally high number of mast cells, a type of immune cell that contributes to anaphylaxis and other allergic symptoms by releasing histamine and other chemicals that cause inflammation. The participants with ISM had more severe reactions than those without ISM, even though they had lower levels of antibodies to alpha-gal.

“Alpha-gal allergy appears to be yet another reason to protect oneself from tick bites,” says NIAID Director Dr. Anthony S. Fauci.

“We often think of ticks as carriers of infectious diseases, such as Lyme disease, but the research strongly suggests that bites from this particular species of tick can lead to this unusual allergy,” explains co-author Dr. Melody C. Carter at NIAID. “The association is increasingly clear, but we still need to discover exactly how these two events are linked and why some people with similar exposure to tick bites seem to be more prone to developing alpha-gal allergy than others.”