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ORLANDO -- The food allergy alpha-gal, which causes symptoms from runny nose to life-threatening anaphylaxis in reaction to eating red meat, remains a bit of a mystery, said researchers here.

But what is known challenges the paradigm of food allergy as it is currently understood, according to one presenter at the American Academy of Allergy, Asthma & Immunology and World Allergy Organization meeting.

First described close to a decade ago, alpha-gal allergy is a reaction to the sugar molecule galactose-α-1,3-galactose, found in beef, pork, lamb, and other red meats. It appears to be triggered by the bite of some, but not all, tick species.

Maya R. Jerath, MD, PhD, of Washington University School of Medicine in St. Louis reported that people with alpha-gal allergy were five times as likely as people without the allergy to be sensitized to venom allergens from stinging insects such as wasps, honey bees, hornets, and fire ants. The finding suggests that "development of IgE following ecto-parasitic tick bites and stinging insect envenomation may have a shared immunologic determinant or predisposition other than just atopy," her group noted.

Jonathan Brestoff, MD, PhD, also from Washington University, and colleagues reported that people with blood types B or AB were five times less likely than those with other blood types to be diagnosed with a red meat allergy (OR 0.20, 95% CI, 0.07-0.62, P=0.004).

Finally, findings from a single-center longitudinal analysis by Philip L. Lieberman, MD, of the University of Tennessee Health College of Medicine in Memphis, and colleagues, suggested that a large percentage of previously unexplained anaphylaxis cases among adults may be attributable to alpha-gal allergy.

In the study by Lieberman's group, an analysis of 222 anaphylaxis cases seen at the university-affiliated allergy clinic, dating back to 1993, found alpha-gal allergen to be a common cause of sensitization in cases cases with an identified trigger.

Lieberman noted that the percentage of cases with an unknown trigger declined significantly from 59% in 2006, when the red-meat allergy was largely unknown, to 34% in the latest analysis conducted in 2016.

"Alpha-gal was not described in 2006, so we didn't know," he said. "I heard this story over and over about these people who had terrible reactions -- some life threatening -- often waking them up in the middle of the night. But we didn't have any idea what it was until the first (alpha-gal allergy) reports came out around 2008."

In the U.S, red-meat allergy has been largely confined to the southeastern part of the country, spread by the bite of the lone star tick, which is common in the region.

A few cases have been reported in New England, where two other species -- dog ticks and deer ticks -- predominate.

"We are seeing this allergy more worldwide, and different ticks in different regions have been associated with it. There is clearly a strong association with ticks, but I don't think they are the whole story," Jerath told 木瓜直播.

She said her group's finding of an increased sensitivity to stinging insect venom among alpha-gal sensitive people suggest the possibility of other transcutaneous routes.

"Alpha gal is incredibly interesting to us because it challenges just about everything we think we know about food allergies," Jerath said. "We are taught that food allergies have certain characteristics -- that reactions are to a protein; that reactions happen instantaneously or very soon after food ingestion; and that they are 100% reproducible, which is why food challenges are the gold standard for diagnosis."

"But alpha gal is a carbohydrate, not a protein," Jerath noted. "Reactions typically occur 4 to 6 hours after red meat is eaten, and the reaction is not easily reproducible in the clinical setting. Someone with an alpha gal-allergy may eat steak 4 days in a row with no reaction, and on the 5th day, they experience anaphylaxis."