Research Links Bites From Two More Types of Ticks to Alpha-Gal Syndrome
WASHINGTON — Alpha-gal syndrome is a food allergy that causes a reaction to the consumption of red meat. It was thought to be caused by a bite from the lone star tick (Amblyomma americanum); however, two Emerging Infectious Diseases studies have linked it to the black-legged (deer) and western black-legged ticks.
In one study, Centers for Disease Control and Prevention researchers investigated a woman in Maine who experienced AGS symptoms nine days after being bitten by a black-legged tick (Ixodes scapularis). The woman found the tick on her arm after taking a walk in the woods. She removed it and correctly identified it.
Three days after being bitten, the woman found the bite had become inflamed and itchy. The patient’s first gastrointestinal symptoms occurred May 13, nine days after the tick bite and two-and-a-half hours after a meal of roasted rabbit and an alcoholic beverage.
Symptoms, including delayed-onset abdominal pain and malaise, continued to occur over the next two weeks after meals containing red meat. All meals were shared but no one else experienced symptoms. A severe episode of diarrhea and vomiting hours after beef consumption prompted the patient to visit a health care provider 20 days after the initial bite.
Blood tests revealed a serum alpha-gal–specific IgE level above the upper limit of detection, and the woman’s health care provider recommended avoiding beef, lamb and pork.
Ten months after the initial symptoms, the patient ate a steak dinner then a roast beef sandwich and did not experience any symptoms. She started eating red meat again.
The CDC went on to confirm AGS in 23 Maine residents identified through retrospective surveillance.
In a second study, in May 2017, researchers in Washington state investigated a woman who had symptom onset after tick bites and had no exposure to areas with known lone star ticks within the previous 30 years.
Over the next several weeks following the bite, the woman experienced severe symptoms including a swollen tongue, difficulty breathing and speaking, and elevated heart rate and blood pressure.
Later, the patient remembered that she had walked her dog in a wooded area the month before and experienced itching on her back. She found a non-engorged tick embedded in her left shoulder, which had likely been there for about 12 hours.
After she removed parts of the tick, the bite area became painful and red. The same day, she sought care, and the mouthparts were removed and doxycycline was prescribed.
The woman followed this up with a visit to an allergist, who detected elevated alpha-gal IgE levels, diagnosed AGS, told her to avoid eating red meat, and cautioned her about consuming milk and gelatin. She followed the advice and had no further allergic episodes, and within six months, her alpha-gal IgE level had fallen markedly.
The patient reported two more bites with Ixodes 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 concluded: “We provide evidence that bites from I. pacificus ticks might stimulate an IgE response leading to AGS, particularly after repeated tick bites. In addition, we highlight the value of passive tick surveillance programs, which led to public health reporting of this uncommon finding. Providers should consider AGS as a cause of anaphylaxis in the western United States. Public health practitioners across the United States should continue efforts focused on tick bite prevention, health care provider education, and improved tick and tick borne disease surveillance.”
The CDC has scaled up surveillance and advised clinicians and health care professionals to routinely screen tick bite patients for alpha-gal–specific IgEs.
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