AGA: Consider alpha-gal syndrome for unexplained GI symptoms in Lone star tick territory
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Key takeaways:
- Clinicians should consider alpha-gal syndrome in patients with unexplained GI symptoms and test for alpha-gal IgE antibodies.
- Patients should avoid tick bites and eliminate mammalian meat from their diet.
The AGA has published a new clinical practice update on the diagnosis and management of patients with alpha-gal syndrome, an emerging food allergy that manifests with common gastrointestinal symptoms and is caused by Lone Star tick bites.
“We wrote the update to heighten gastroenterologists’ awareness of alpha-gal syndrome,” Sarah K. McGill, MD, MSc, associate professor of gastroenterology and hepatology at the University of North Carolina at Chapel Hill and co-author of the update, told Healio. “Patients with alpha-gal syndrome can present with chronic or recurrent GI symptoms without rash or anaphylaxis, so they can end up in GI clinicians’ offices seeking relief.”
According to McGill and colleagues, who first described GI alpha-gal syndrome in the literature a few years ago, the condition is caused by an immunoglobulin E-mediated reaction hours after eating beef, pork, other mammalian meat or mammalian-derived products.
“The allergy in alpha-gal syndrome is to galactose alpha-1,3-galactose, an oligosaccharide on the cells of all non-primate mammals,” they wrote in Clinical Gastroenterology and Hepatology. “Surprisingly, sensitization to alpha-gal, ie, the process by which humans develop IgE antibodies to the sugar, is understood to occur after the bite of a tick or parasitic infection. In the United States, the Lone Star tick, an ectoparasite whose principal host is deer, is strongly implicated.”
Though most individuals with alpha-gal antibodies are asymptomatic, some patients present with delayed allergic reactions, including hives or a drop in blood pressure consistent with anaphylaxis, 3 to 5 hours after meat consumption. They may also have abdominal symptoms, particularly pain.
Without specific blood testing for IgE to alpha-gal, researchers noted patients may be diagnosed with irritable bowel syndrome or other functional GI disorders.
When to consider an alpha-gal syndrome diagnosis
Clinicians should consider alpha-gal syndrome in patients with unexplained GI symptoms and, particularly, in individuals who live or have lived in alpha-gal prevalent areas, which geographically mirror the range of Amblyomma americanum, known as the Lone Star tick.
In addition, a history of waking at night with GI distress and a history of tick bites or participating in outdoor activities may suggest alpha-gal.
“Alpha-gal syndrome is prevalent in the Southeast, Midwest and Mid-Atlantic states. Symptoms can include abdominal pain, diarrhea and vomiting, and occur a few hours after alpha-gal ingestion, which makes the diagnosis of a food allergy very challenging,” McGill told Healio. “The syndrome is transmitted with a tick bite. GI clinicians can screen for the syndrome with a blood test (IgE alpha-gal) but to make the diagnosis, patients should have significant relief of their symptoms with an alpha-gal avoidant diet.”
Patient management and follow-up
Following an alpha-gal diagnosis, management involves elimination. Patients should be counseled to not ingest pork, beef, venison and other mammalian meat as well as related products such as lard, butter and milk. Foods containing gelatin, processed foods and cross-contaminated items also may be problematic among those with high levels of sensitivity. McGill and colleagues noted that fish, seafood, turkey, chicken and other fowl are acceptable for consumption.
Patients with alpha-gal also should avoid additional tick bites, as they may worsen their allergy. Referral to an allergist is recommended when a patient reports skin or systemic changes such as swelling of the face or throat, voice changes, difficulty breathing, hives or fainting with reactions.
“Alpha-gal syndrome was first described less than 20 years ago and we described the GI phenotype just 2 years ago, so there is a lot we do not know,” McGill said. “We do not understand why some people get GI symptoms alone. We have not confirmed the GI patients’ allergy with a double-blind food challenge, which is the gold standard for allergy diagnosis. We also do not understand why patients do not consistently react to alpha-gal ingestions, which seems to be unique among food allergies.”
She continued: “I am hopeful that including alpha-gal screening into the diagnostic algorithm for unexplained GI symptoms in alpha-gal prevalent regions will lead to faster diagnosis and more effective care for these patients.”
Perspective
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Christine Lee, MD
Raising awareness for alpha-gal syndrome is important to all medical care providers, particularly those who provide care in tick endemic areas of the U.S. It is estimated that over 32 million Americans suffer from food allergies. Some allergic reactions have been known to cause significant morbidity and even mortality.
The number of confirmed cases of alpha-gal syndrome in the U.S. has jumped from a mere 12 reported cases in 2009 to 34,000 cases in 2019. Alpha-gal syndrome is now one of the leading causes of onset of allergy and anaphylaxis in adults in the U.S. and raising awareness can lead to earlier diagnosis and treatment.
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