(Reuters Health) - Meat allergies related to tick bites might be at the root of some unexplained severe, life-threatening allergic reactions, a new study suggests.

Researchers poring through records from a Tennessee clinic found that a large percentage of anaphylactic shock cases were sparked by an allergy to alpha-gal, a complex sugar found in red meat, according to a report in Annals of Allergy, Asthma and Immunology.

Even so, anaphylaxis due to alpha-gal is still pretty rare, said study coauthor Dr. Jay Lieberman of the University of Tennessee Health Science Center and Le Bonheur Children’s Hospital.

“I don’t want this to lead to hysteria,” said, Lieberman who is also vice chair of the American College of Allergy, Asthma and Immunology Food Allergy Committee. “The vast majority of people with a history of tick bites are not going to develop this allergy to meat and will continue to eat meat with no problem, even among those with positive antibody tests to alpha-gal. It’s just a small proportion who will actually have symptoms.”

Those symptoms can include hives; swollen lips, eyes, tongue and throat; trouble breathing; vomiting; diarrhea; increased heart rate and low blood pressure.

No one knows exactly how many Americans have developed a meat allergy from a tick bite. But “current estimates from multiple studies across institutions in the U.S. are that approximately 5,000 people have developed the alpha-gal red meat allergy,” said Dr. Scott Commins, an associate professor of medicine and pediatrics at the Thurston Research Center at the University of Carolina, Chapel Hill. Commins is not affiliated with the new research.

Lieberman’s team hopes the study will remind doctors and patients that the meat allergy could be the cause of unexplained anaphylaxis. Many are not aware because the tick-related allergy was only recently discovered.

About a decade ago, scientists figured out the connection between lone star tick bites and an allergy that some patients were developing to red meat. Current thinking is that ticks pick up alpha-gal, which is in all red meat, after biting a deer. When the tick bites a human, it passes along the alpha-gal. In some people, when the alpha-gal enters the bloodstream, the immune system flags the unfamiliar molecules as enemy invaders.

One big difference between alpha-gal sensitivity and other food allergies is how long it takes to react after eating. While typical food allergies may cause a reaction within minutes, the alpha-gal response can occur three to six hours after exposure, making it harder to connect the dots between the food and the body’s response to it.

Lieberman and colleagues reexamined 218 cases of anaphylaxis treated between 2006 and 2016. Before their new review, the cause of anaphylaxis in nearly 60 percent of patients who came to the clinic couldn’t be diagnosed. After the review, that percentage dropped considerably, Lieberman said.

Eighty-five cases (39 percent) were classified as having a definitive cause. Among these, 28 cases (33 percent) were attributed to alpha-gal. Most of the others were attributed to food allergies (most often shellfish, followed by peanuts, tree nuts, fish, and milk). Causes for the rest included venom, medications, and other allergens.

Another 57 cases (26 percent) were classified as having a probable cause. In this group, 26 percent were most likely due to alpha-gal sensitivity, 35 percent to other food allergies, 23 percent to medication sensitivity, 5 percent to venom, and 11 percent to some other sensitivity.

Experts said the new study is an important heads-up to patients and the medical community. “Providers and patients - especially those living in tick-populated areas - should be aware of the delayed allergic reactions,” Commins said in an email.

Checking for alpha-gal sensitivity may soon become standard of care, said Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security in Baltimore, Maryland.

"Patients who experienced anaphylactic shock and didn't get a good explanation for it should take a look at the Centers for Disease Control and Prevention's maps and if they live in an area where the lone star tick is common, they should talk to their doctor about investigating whether it was caused by alpha-gal sensitivity," Adalja said. (bit.ly/2K8f7m2)

SOURCE: bit.ly/2K7zzU4 Annals of Allergy, Asthma and Immunology, online July 30, 2018.