Diagnostic dilemma: Hunter's rare allergy meant he could no longer eat red meat

The patient: A 47-year-old man in Michigan

The symptoms: The patient went to a hospital emergency room with swollen eyelids and an itchy rash. He told his doctors that these symptoms arose a day earlier, and since their appearance, he intermittently felt like he was going to faint. For five days before visiting the hospital, he had cramps, nausea, abdominal pain and vomiting. Three weeks prior to that, he had developed watery stools after eating.

When the hospital doctors examined the patient, they found that his blood pressure was unusually low and his heart was beating faster than normal. His lips were swollen and he had hives on his scalp, neck, torso and groin. In some places, small hives had merged together to form large welts. These were all symptoms of anaphylaxis, a severe allergic reaction that can affect swallowing and breathing, the doctors wrote in a report of the case.

What happened next: During the examination, the patient's symptoms worsened and he began developing signs of shock, a life-threatening condition in which the body's organs and tissues do not receive enough blood. He received intravenous fluids, antibiotics, the antacid famotidine for excess stomach acid, and a steroid to reduce inflammation. Doctors also gave him an injection of epinephrine, also known as adrenaline, to treat his allergic symptoms. (Epinephrine is the substance found in EpiPens.)

Once the man's heart rate and blood pressure stabilized within a normal range, he was admitted to the hospital's intensive care unit.

The patient said that he had no known allergies other than a mild sensitivity to the antibiotic penicillin. There was no history of allergies in his family, and he had not recently eaten any foods that he had never had before. However, because the patient had experienced weeks of diarrhea and days of abdominal pain prior to his hospital visit, the physicians suspected that his allergic symptoms were caused by a newly acquired food allergy. The fact that his symptoms intensified over time also suggested he'd had repeated exposures to the allergen.

Having abated, the patient's symptoms then returned on his fourth day at the hospital, and included tightness in his chest, wheezing and shortness of breath. He received another dose of epinephrine, and his symptoms went away almost immediately. When doctors questioned the patient, he said that he had eaten beef spare ribs about four hours earlier. He also recalled that he had eaten venison two days before being admitted to the emergency room.

The diagnosis: Since the mid-2000s, scientists have become aware of a condition called alpha-gal syndrome, a type of food allergy triggered by a sugar found in red meat and other products from mammals, such as gelatin or milk. It is most often caused by the bite of the lone star tick (Amblyomma americanum), though some other tick species can cause it, too.

The patient reported being a habitual meat-eater and a deer hunter, and white-tailed deer (Odocoileus virginianus) are known hosts for the lone star tick. While the man did not remember being bitten by a tick, based on his symptoms and the timing of their appearance, the physicians concluded that the man had developed alpha-gal syndrome after a tick bite, "perhaps from small larval ('seed') ticks, in the weeks before the symptoms of alpha-gal syndrome manifested," the doctors wrote in the report.

Initially, his allergic reactions manifested as abdominal distress, and they then intensified over time as he continued to eat more red meat.

The treatment: The doctors instructed the patient to avoid eating red meat. He was discharged from the hospital and given steroids to reduce inflammation. He also received an antihistamine called diphenhydramine, to be used as needed, and an intramuscular epinephrine autoinjector. In a follow-up visit 15 months later, the patient reported that he had abstained from eating meat and there had been no more anaphylaxis incidents.

What makes the case unique: Meat is an uncommon food allergen, and many healthcare providers are unfamiliar with alpha-gal syndrome, the Centers for Disease Control and Prevention reported in 2023. Among the medical providers who do know about the syndrome, few are familiar with diagnosing and managing it.

Additionally, the lone star tick was previously rare in Michigan but its range has greatly expanded in recent years. This is primarily due to climate change — ticks can now live in places that were previously too cold for them — and human activities that fragment habitats and reduce biodiversity. Deer are the preferred host for lone star ticks, and as such, less diverse ecosystems that are dominated by deer are more hospitable to this tick species.

It's not fully understood how ticks trigger the meat allergy, but some research finds that the pests likely produce alpha-gal antigens and secrete them in their saliva. The syndrome is increasingly being recognized as a threat to public health around the world, according to the report.