Two Additional Tick Species Tied to Skyrocketing Incidence of Alpha-Gal Syndrome

Alpha-gal syndrome (AGS) is an acquired allergy to alpha-gal, a sugar molecule found in the tissues of most mammals except for humans and other primates. It occurs when a person is bitten by a tick — notably the lone star tick — that carries alpha-gal from previous bites. The tick injects the alpha-gal into the person’s body, which triggers the immune system to produce antibodies against it.

The incidence of Alpha-gal syndrome (AGS) has been on the rise along with the expanding territory of the lone star tick. The US Centers for Disease Control and Prevention (CDC) estimates that AGS already affects up to 450,000 Americans.

Now, two new studies appearing in the journal Emerging Infectious Diseases link bites from black-legged (deer) and western black-legged ticks to the development of AGS.

In the first study, a team led by CDC researchers investigated a patient in Maine who showed AGS symptoms nine days after a black-legged tick (Ixodes scapularis) bite in May 2022.

The 45-year-old woman removed a black-legged tick from her left bicep after a walk on a wooded path in York County. Three days later, the bite area became inflamed and itchy and featured an enlarged red circumference. Nine days after the bite, she developed GI symptoms after eating roasted rabbit and having an alcoholic drink. She continued to suffer abdominal pain and malaise for two weeks after eating red meat and sought care 20 days post-bite after experiencing a severe bout of vomiting and diarrhea after eating beef. 

Blood tests revealed a serum alpha-gal–specific IgE level above the upper limit of detection, and the woman’s clinician recommended avoiding beef, lamb, and pork.

In Washington state, a Kaiser Permanente Seattle–led team detailed a case of alpha-gal syndrome in a state resident bitten by a western black-legged (Ixodes pacificus) tick.

The 61-year-old woman who worked as a wildlife biologist reported diffuse urticaria (hives) and lip swelling to a nurse, who advised her to take the antihistamines. Her symptoms resolved within 24 hours. 

A month later, the woman called emergency services after experiencing itching in her groin, urticaria on her back, rapid-onset tongue swelling, and dA month later, the woman called emergency services after experiencing itching in her groin, hives on her back, rapid swelling of her tongue, and difficulty speaking. The paramedics noted wheezing, low blood pressure, and a fast heart rate, so they administered epinephrine to treat her anaphylaxis. While her condition improved slightly at first, within several minutes, the paramedics documented a worsening of her symptoms, including increased tongue swelling, tightness in her throat, and tunnel vision, and difficulty speaking. After noting wheezing, low blood pressure, and a high heart rate, paramedics administered epinephrine for anaphylaxis. Her condition improved slightly, but within several minutes, paramedics documented worsening tongue swelling, throat tightness, and tunnel vision.

The woman received a second dose of epinephrine, and after her symptoms worsened in the ambulance, she also received the corticosteroid methylprednisolone and an epinephrine nebulizer. Her symptoms improved in the emergency department (ED), and she was released home with prescriptions for prednisone, the antihistamines famotidine and diphenhydramine, and an epinephrine auto-injector.

The woman visited an allergist, who detected elevated alpha-gal IgE levels, diagnosed AGS, told her to avoid eating mammalian meat, and cautioned her about consuming milk and gelatin. She then avoided meat and gelatin and had no further allergic episodes, and within 6 months, her alpha-gal IgE level had fallen markedly.

The patient reported two more bites with I pacificus ticks in April 2020 and March 2022, after which she experienced similar itchy reactions at the bite site, as well as elevated alpha-gal IgE levels.

The researchers wrote:

Had the patient not switched to a vegetarian diet, clinical experience suggests that the rise in IgE titer might have increased her chances of having an allergic reaction after red meat consumption.

Additional work will be needed to determine a possible link between I. pacificus or other Ixodes spp. ticks and AGS in the United States. Public health practitioners across the United States should continue efforts focused on tick bite prevention, healthcare provider education, and improved tick and tickborne disease surveillance.