An allergy clinic in Tennessee has found that 33 percent of their anaphylaxis cases of known cause were due to an allergic reaction to a molecule called alpha-gal. This molecule naturally occurs in red meats, such as beef, lamb, pork, and venison.
The red meat allergy develops in people who have been bitten by the Lone Star tick, a small eight-legged bug that is most commonly found in the Southeastern United States.
The researchers say that alpha-gal allergy used to be "an unknown entity" at the allergy clinic in the University of Tennessee Health Science Center in Memphis.
However, as awareness has increased and diagnostic tests have become available, the tick-induced red meat allergy has become the center's "most commonly identified cause of anaphylaxis."
A paper on the findings is shortly to be published in the Annals of Allergy, Asthma and Immunology.
Red meat allergy
Allergic reactions to foods can cause symptoms that range from mild to a severe, life-threatening condition called anaphylaxis that makes it hard to breathe and causes blood pressure to drop.
Although the exact prevalence of the red meat allergy is largely unknown, it seems to predominantly affect those living in the Southeast U.S. and also in certain parts of New England, New Jersey, and New York.
In most cases, a reaction to foods that most commonly cause allergy — for example some types of shellfish and peanuts — is usually rapid, with symptoms beginning within 30 minutes of exposure.
But in alpha-gal allergy, the reaction is much slower, and symptoms can take up to 6 hours to emerge after eating red meat. This makes it much harder to identify the cause. Now, it is possible to diagnose it with a blood test.
While the link between Lone Star tick bites and alpha-gal allergy is now clear, scientists do not fully understand the biology of the connection.
'Clear cause of anaphylaxis'
For the study, researchers reviewed cases between 2006 to 2016. They identified 218 cases of anaphylaxis in which the cause was known and found that 33 percent were due to a reaction to alpha-gal.
"When we did the same review in 1993," says lead study author Debendra Pattanaik, an associate professor of medicine and rheumatology at the University of Tennessee Health Science Center, "and again in 2006, we had a great many cases where the cause of the anaphylaxis couldn't be identified."
"Our research clearly identified alpha-gal as the cause of anaphylaxis in the majority of cases where the cause was detected."
Prof. Debendra Pattanaik
The researchers found that the second most common cause was food allergies, which accounted for 24 percent of anaphylaxis cases.
This was followed by reactions to insect bites (accounting for 18 percent of cases), exercise (6 percent of cases), a condition called systemic mastocystosis (6 percent), and reactions to medicines and other causes (4 percent and 3 percent, respectively).
They also found that the number of unidentified cases of anaphylaxis fell from 59 percent to 35 percent over the same period, most likely due to improved diagnosis of alpha-gal allergy.