Alpha-gal syndrome (AGS) is an acquired allergic reaction to galactose-α-1,3-galactose (alpha-gal), a carbohydrate found in mammalian meat (e.g., pork, beef, rabbit, lamb, etc) and products made from mammals (e.g., gelatin, cow’s milk, milk products). And it’s caused by tick bites. And can it happen to pretty much anybody. Seriously.
Many ticks (especially lone star ticks—the most common culprit) express alpha-gal in their salivary glands, so a tick bite can potentially transfer alpha-gal into a person’s bloodstream. In affected patients, this transfer triggers production of specific IgE which in turn can cause a delayed allergic reaction after these patients eat food products containing alpha-gal; for unclear reasons, this reaction occurs much more often after eating meat as opposed to dairy products.
In a recent study, around 120 patients who tested positive for AGS (out of 1260 who were tested) most often exhibited urticaria (56%), angioedema (38%), anaphylaxis (36%), diarrhea (32%), nausea (31%), vomiting (23%), abdominal pain (22%), and cramps (18%); 11% of patients reported only GI symptoms. Symptoms started within 1 hour of ingestion in 11% and were delayed by >4 hours in 29%. Most patients had symptoms only with red meat consumption, but 11% had symptoms after milk consumption. Among patients with 2-year follow-up data, about one in six successfully reintroduced red meat into their diets.
Because of the variability in clinical presentation, age of onset, and delayed reaction time, it should come as no surprise that the diagnosis of AGS is likely easily missed or misclassified (e.g., idiopathic anaphylaxis, IBS, etc). Diagnosis requires the combination of clinical symptoms with positive alpha-gal IgE serology (sensitivity 100%, specificity 92%). Management of AGS is avoidance of products containing alpha-gal and provision of an epipen and allergy action plan.