May 21, 2019

The Story of Alpha-gal: Allergy to Red Meat after a Tick Bite

By Christina Funari Ortiz, MD, MPH


Ticks are often implicated in infectious disease, but rarely, if ever, has the allergy community considered ticks important in the spread of food allergy – until recently. 

One such tick-associated food allergy is referred to as “alpha-gal,” which is an allergy to red meat. This was first reported in the 1990s; however, advances in research, augmented by epidemiologic insight, lead to a full description by University of Virginia researchers in 2009.

Alpha-gal is a delayed food allergy to mammalian meat. It is spread by the Lone Star tick, which is found largely in the southeastern United States and is very common in Hampton Roads. The Lone Star tick bites both humans and animals, and in the event of a mammalian bite, it ingests a complex sugar called galactose-alpha-1,3-galactose, or alpha-gal. This sugar is a component of the cell membrane in most mammals but is not found in humans, a distinction important to the nature of how the allergy is transmitted. When the tick bites a human, it subsequently transfers the sugar ingested from a previous mammalian bite and activates the immune system to make allergic antibodies to alpha-gal.  

People with these allergic antibodies mount a delayed reaction after ingestion. The time-frame for reaction is about three to six hours after ingesting mammalian meats, including beef, pork, lamb, and sometimes even milk or butter. Reactions vary in severity and may involve hives or progression to anaphylaxis. Symptoms can include swelling, difficulty breathing or swallowing, nausea/vomiting and, at times, a decrease in blood pressure. 

Alpha-gal can be difficult to diagnosis as, in many cases, patients do not associate the meat they have eaten with the reaction due to the time span between the two events. This is a serious and potentially life-threatening condition, and patients have reported waking in the middle of the night with severe hives or even anaphylaxis that requires administration of epinephrine.  

If you or your patient suspect an alpha-gal allergy, evaluation by an allergist is recommended. If indicated, this allergy is diagnosed after a thorough consultation and blood testing. The current treatment recommendation is a strict avoidance diet of all mammalian meats and, at times, mammalian products, which can include the gelatin found in various medications. Interestingly, certain vaccine products also contain gelatin, and alpha-gal has been implicated in anaphylactic reactions to both the Zoster and MMR vaccines. Although rare, a minority of alpha-gal patients may react to vaccines or medications, but it is not yet possible to test for this reactivity. 

In addition to the strict avoidance of red meat, patients diagnosed with an alpha-gal meat allergy are prescribed an EpiPen and monitored closely each year, as the allergy can dissipate over time. There is a possibility of re-introducing mammalian meats into the diet as the allergy changes; however, it is not yet clear how often or how likely this is the case. Re-introduction should only be performed in a supervised setting with emergency medical equipment and trained personnel close by.

Dr. Christina Funari Ortiz is a fellowship trained allergy specialist at TPMG Coastal Allergy in Chesapeake and Virginia Beach.