Detected within the last two decades, Alpha-gal Syndrome (AGS) is a series of allergic reactions to the Alpha-gal carbohydrate present in non-primate mammalian meat and derivative products, such as dairy, gelatin and collagen. AGS is transmitted to humans by ticks, with the Lone Star tick believed to be responsible for most cases in the United States. However, cases have been reported in every country except Antarctica, leaving other species of tick as potential transmitters.
One of the key presenting features of AGS is the delay in symptom onset. The severity of symptoms also can differ among individuals, and a reaction may not occur after each exposure to a food containing AGS. Complaints of abdominal pain, diarrhea, vomiting, rashes, itchy skin, angioedema and anaphylaxis may appear with an onset of one to six hours after ingestion of the problem food, or a more instantaneous reaction of two to 15 minutes after taking certain medications containing mammalian byproducts, such as the chemotherapy agent cetuximab. Heparin, pancreatic enzymes, vaccines grown in mammalian cells and mammalian heart valves also may produce reactions for those with severe AGS. According to the Centers for Disease Control and Prevention, reactions to medications and vaccinations are very rare; however, it is recommended that individuals discuss it with a health care provider prior to taking any new medications or receiving a new vaccine.
When it comes to identifying cases of AGS, health care providers may still overlook this emerging condition. The CDC released a recent report indicating 42% of health care providers were unaware of Alpha-gal syndrome and 35% were not confident in their ability to treat the condition. A clinical practice update by the American Gastroenterological Association suggests the potential that with delayed onset of symptoms and overlap of gastrointestinal complaints, patients with AGS may be misdiagnosed with other gastrointestinal conditions such as irritable bowel syndrome. They encourage gastroenterologists to raise awareness of AGS and to refer patients who are diagnosed to a registered dietitian nutritionist for a trial of an AGS-avoidance diet for at least one month.
When medical history indicates testing is appropriate, anti-alpha-gal IgE titers are the preferred diagnostic tool. Skin prick tests lack sensitivity for AGS and given the delayed nature of the syndrome, oral food challenges are often inappropriate due to the high-level of risk with the limited observation window.
Preventative measures against tick bites are the primary defense against contracting AGS, as there is currently no known cure, and studies indicate that additional tick bites may worsen AGS symptoms. Alternatively, individuals who have avoided further tick bites often find improved tolerance to meat and other animal products over time. However, diet is a cornerstone of AGS management once it has been contracted.
Meat from mammals such as beef, pork and venison are generally not tolerated by those with AGS. Gelatin and collagens also should be avoided. Dairy contains lower amounts of alpha-gal, and these products are more likely to be tolerated than meat by individuals with less severe reactions. Poultry, fish and seafood are often acceptable protein options. Fruits, vegetables and grains also are still encouraged and are not known to cause reactions.
Some additional factors have been reported to increase severity of reactions among those with AGS, such as consuming nonsteroidal anti-inflammatory drugs or alcohol and being physically active before eating problematic foods.
- Young I, Prematunge C, Pussegoda K, Corrin T, Waddell L. Tick exposures and alpha-gal syndrome: A systematic review of the evidence. Ticks Tick Borne Dis. 2021;12(3):101674.
- Vaz-Rodrigues R, Mazuecos L, de la Fuente J. Current and Future Strategies for the Diagnosis and Treatment of the Alpha-Gal Syndrome (AGS). J Asthma Allergy. 2022;15:957-970.
- McGill SK, Hashash JG, Platts-Mills TA. AGA Clinical Practice Update on Alpha-Gal Syndrome for the GI Clinician: Commentary. Clin Gastroenterol Hepatol. 2023;21(4):891-896.
- Centers for Disease Control and Prevention. Alpha-gal Syndrome. Accessed August 24, 2023.
- Carpenter A, Drexler NA, McCormick DW, et al. Health Care Provider Knowledge Regarding Alpha-gal Syndrome — United States, March–May 2022. MMWR Morb Mortal Wkly Rep. 2023;72:809–814.
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