A Half-Million Americans May Have Tick-Linked Meat Allergy, C.D.C. Says

As many as 450,000 Americans may be living with alpha-gal syndrome, a meat allergy that has been linked to tick bites, with many of those people going undiagnosed, according to two new studies from the Centers for Disease Control and Prevention.

In one of the new studies, both of which were published on Thursday, scientists reviewed the laboratory results of people who had been tested for the telltale antibodies, identifying 110,000 suspected cases since 2010.

But that figure is probably a significant underestimate. In the second study, researchers found that 78 percent of health care providers who were surveyed had little or no knowledge of the condition, and many clinicians who had heard of the syndrome were not sure how to diagnose it.

“Our 110,000 suspected cases of alpha-gal syndrome represent those that found the health care provider that did properly send off for the antibody test,” said Dr. Johanna Salzer, a disease ecologist and veterinarian at the C.D.C. and an author of both studies.

When the researchers factored in this knowledge gap, they estimated that the true toll of the syndrome might be closer to a half-million, although Dr. Salzer acknowledged that the figure was “a crude estimate.”

Still, it is clear that the condition is significantly underdiagnosed, said Dr. Maya Jerath, an allergist and immunologist at Washington University in St. Louis, who has treated hundreds of patients with alpha-gal syndrome. “This is a story that every patient of mine tells me, that ‘I had to go to five physicians before they could tell me what it was,’” said Dr. Jerath, who was not involved in the new studies. “It’s nice to have numbers behind it, and it’s definitely a call to action.”

Alpha-gal syndrome, which was not formally identified until the 2000s, takes its name from galactose-alpha-1,3-galactose, a sugar present in beef, pork, lamb and the meat of most other mammals. (It is not present in humans or other apes.) Lone star ticks, which scientists believe are the primary culprits of the disease in the United States, can transmit the sugar to people through a bite. Some people’s immune systems may then label this foreign sugar a threat and overreact to its presence the next time they eat meat.

The symptoms, which often take hours to appear, are wide-ranging, and may include hives, nausea, diarrhea or anaphylactic shock. Even patients who have the syndrome may not feel sick every time they eat meat. “It’s consistently inconsistent,” Dr. Salzer said. “So this makes it a real challenge for health care providers.”

To diagnose the syndrome, clinicians can order a blood test to determine whether a patient has antibodies to alpha-gal. Until August 2021, a single commercial lab did nearly all of this antibody testing in the United States. In one of the new studies, researchers reviewed the results of the antibody tests performed at this lab from 2017 to 2022.

In total, more than 90,000 people received positive tests over that time period, and the number of people with positive tests increased annually, from about 13,000 in 2017 to nearly 19,000 in 2021. Roughly 20,000 cases had been identified in an earlier study, yielding a total of 110,000 suspected cases from 2010 to 2022.

The rising number of cases identified annually could stem from increasing awareness, an increase in the true prevalence of the syndrome or a combination of both. Lone star ticks are expanding their range, likely as a result of climate change, and other diseases they carry, such as ehrlichiosis, have also become more common in recent years.

Alpha-gal syndrome was most common across a large swath of Southern, Mid-Atlantic and Midwestern states, where the lone star tick is known to live, the researchers found.

But there were also clusters in northern Minnesota and Wisconsin, which are not known to be homes for the ticks. Although some of the people who tested positive may have acquired the disease elsewhere, the results also highlight how much remains unknown about alpha-gal syndrome. “I don’t think that the lone star tick is the full story,” Dr. Jerath said.

In a second study, researchers surveyed 1,500 clinicians, including doctors, nurse practitioners and physician assistants, using an online survey. They found that 42 percent of participants had not heard of alpha-gal syndrome. An additional 35 percent said they were “not too confident” that they could diagnose the illness or manage patients who had it. Of the clinicians who did know about the syndrome, 48 percent said they did not know what test they should order to diagnose it.

Dr. Salzer stressed the importance of tick bite prevention, noting that unlike some other tick-borne diseases, alpha-gal syndrome has no treatment or cure. “Alpha-gal syndrome can be a lifelong condition,” Dr. Salzer said. “It definitely needs to be a part of the conversation of why tick prevention is so important for public health.”