I’ll Have the Veggie Burger, Please
Alpha-gal syndrome is a more recently discovered allergy to meat that is most often caused by a tick bite. In 2006, cetuximab was approved as a cancer treatment for head and neck cancer and colon cancer. There were multiple cases of allergic reactions to this medication. Around the same time, there had been cases of adults having allergic reactions several hours after eating but with no known obvious cause. Through diligent research, doctors found that the reaction was to a carbohydrate known as galactose-alpha-1,3-galactose, called alpha-gal for short. Further investigation led them to find that all the cases seemed to be in the same geographic area where Rocky Mountain Spotty Fever, a tick-borne illness, was seen. They discovered that this allergy was induced by tick bites from the lone start tick, Amblyomma americanum.
It is thought that these ticks carry the alpha-gal molecules from the blood of the animals they bite. Then when they bite a human, they inject the alpha-gal into the person’s body. It is not known exactly why, but being bitten by the lone star tick in some people will cause them to develop the allergic antibody (IgE) to alpha-gal.
Alpha-gal syndrome typically presents in adulthood but can occur in late childhood. People could previously tolerate meat without any problems. Then they start to develop symptoms ranging from hives, swelling, abdominal pain, diarrhea, difficulty breathing, lightheadedness, and passing out after eating. Symptoms can by mild to anaphylactic shock. Symptoms typically occur about 2-6 hours after ingesting non-primate mammalian meat such as beef, pork, lamb, and deer. Alpha-gal is usually diagnosed by an allergist using a thorough history and a blood test. The primary treatment is avoidance of mammalian meat and carrying an epinephrine autoinjector in case of accidental exposure. In some cases, people can also react to organs (such as kidneys or liver), gelatin that may be used in candies/marshmallows, and dairy products such as milk and cheese. There are also non-food products that may contain mammalian products such as colloid plasma substitute, some vaccines, pancreatic enzymes, and bovine and porcine heart valves. Not everyone will have to avoid all of these, and this should be discussed on a case-by-case basis with the patient’s allergist. In general, avoidance of mammalian meat is sufficient in 80% of patients. Another 5-20% will also need to avoid gelatin and dairy. Less than 1% usually have to avoid all products that may be derived from mammals. It is important to avoid further tick bites as this can maintain or lead to increases in the allergic antibody to alpha-gal. Avoidance of tick bites can lead to decreases in the level of this allergic antibody. In some cases, it can become negative, and some people are able to add mammalian meat back in their diet.
Alpha-gal is different than the typical food allergies you think of such as to peanuts or shellfish in a few ways. First, alpha-gal is an allergy to a carbohydrate, and most food allergies are to proteins. Second, most food allergy symptoms present immediately after ingestion; whereas, symptoms are usually a few hours after eating the offending food in alpha-gal. Lastly, alpha-gal usually presents in adults whereas most other food allergies usually present in childhood. The best way to prevent the development of alpha-gal syndrome is to avoid tick bites. The lone star tick is in Texas, and I have seen several cases of alpha-gal. If you are having allergic reactions and are not sure of the cause or think you might have alpha-gal, see a board-certified allergist.