Report from AAAAI/WAO 2018: Reactions to Red Meat Are Rewriting the Rules for Food Allergies
Red meat allergy – also called mammalian meat allergy or alpha-gal allergy – disrupts many of our food allergy assumptions.
This weekend, representatives from FARE are attending a joint congress of the American Academy of Allergy, Asthma & Immunology (AAAAI) and the World Allergy Organization (WAO) in Orlando, FL. We’re reporting on selected abstracts from the meeting that address diverse topics in food allergy. Read on to learn more about featured findings about allergy to a sugar found in red meat. This emerging disease, which differs in many ways from typical food allergies, is becoming increasingly prevalent
Red meat allergy – also called mammalian meat allergy or alpha-gal allergy – disrupts many of our food allergy assumptions.
- Other food allergies are triggered by food proteins, but in the case of red meat allergy, the allergen is a sugar. The alpha-gal sugar is found on the meat proteins of most mammals, but is absent from human proteins.
- For most food allergies, anaphylaxis is rapid or even immediate, but anaphylactic reactions to the alpha-gal in mammalian meat are often delayed, with symptoms developing hours after the meat is eaten.
- Like other food allergies, the risk of developing allergy to red meat is influenced by genetic and environmental factors. However, unlike other food allergies, the primary environmental factor for red meat allergy is being bitten by certain species of tick, and an important genetic factor is ABO blood type.
The bite of lone star tick (named for a central white mark on its back) can trigger red meat allergy in the U.S. Found primarily in the Southern and Central U.S. but currently expanding its range, the tick sucks blood from mammals whose meats contain the alpha-gal sugar. When the tick feeds on a human, it injects residues from previous mammalian meals into the person’s bloodstream, which can sensitize the person to alpha-gal.
Reports of alpha-gal allergy are on the rise. In part, this is because delayed anaphylaxis was more likely in the past to be described as idiopathic (without known cause). However, there is also evidence that incidence of alpha-gal allergy is increasing. One study examined 222 cases of anaphylaxis at a university allergy clinic, going back to 1993. Two-fifths of the cases were determined to have a known cause, one-quarter had a probable cause, and one-third were idiopathic. Among cases with a known cause, the most common trigger was alpha-gal (32 percent), followed by other foods (28 percent).
Other studies investigated risk factors for alpha-gal allergy. Like alpha-gal, the A and B antigens on the surfaces of red blood cells are sugars. These antigens define our blood type as A, B, AB or O. After testing the blood type of 280 people, 92 of whom had a red meat allergy, researchers expected to find the number of individuals with red meat allergy and type B or AB blood to total roughly 20 percent, consistent with blood type frequencies overall. However, less than 5 percent of the individuals with alpha gal allergy had blood that contained B antigen. In other words, people with B or AB blood were five times less likely to develop allergy to red meat. The B antigen and alpha gal sugars have similar structures, so the study authors hypothesize that the immune systems of people with B or AB blood are more likely to ignore alpha-gal as harmless and part of the self.
One risk factor that appears to make alpha-gal allergy more likely is allergy to insect venoms.