Alpha-gal syndrome linked to lone star tick could be more common than known

Lone star ticks are named for the white dot on the females’ backs. Their bites can trigger an allergy to red meat. (Kevin Ambrose for The Washington Post)

5 min

Up to 450,000 people in the United States may have developed a rare and potentially life-threatening tick-associated allergic condition that is triggered when eating red meat, according to federal health data released Thursday.

Alpha-gal syndrome, sometimes known as red-meat allergy, is caused when a tick bites a person and injects a sugar molecule found in its saliva. In some people, that sugar causes an allergic reaction, which can be further triggered by eating red meat, including beef, pork and lamb, because the meat also contains the sugar, known as alpha-gal. Other food products from mammals, such as cow’s milk, other dairy products and gelatin, can also cause allergic reactions. The reactions range from mild, such as hives and itchy rash, to more severe, including difficulty breathing and drops in blood pressure. (Alpha-gal is not found in fish, reptiles, birds or people).

Aside from avoiding those foods and products, there is no treatment or cure.

In the United States, growing evidence links the allergic condition to the lone star tick, an aggressive tick found across the eastern United States but more common in the South, according to the Centers for Disease Control and Prevention. The lone star tick — the adult female has a white dot or “lone star” on her back — also transmits several other illnesses, including the recently identified Heartland virus disease, which can result in fever, fatigue, and in more serious cases, hospitalization and death, according to the CDC.

Longer summers, rising temperatures and the expanding ranges of tick species such as the lone star tick are leading to an increased chance of human exposure to pathogens over a larger geographic area, experts have said.

Diseases spread by ticks, mosquitoes and fleas more than tripled in the U.S. since 2004

In two reports released Thursday, CDC researchers provided the first national estimate of the geographic distribution and magnitude of the emerging condition. Between 2010 and 2022, there were more than 110,000 suspected cases of alpha-gal syndrome, according to one report. That includes test data from a laboratory that was the primary commercial lab responsible for nearly all such testing in the United States before 2022.

But researchers say the number of people who may have been affected is far higher. Because diagnosis requires a positive test and a clinical exam, many people who might have the condition may not get tested because they don’t have access to health care. The CDC estimates that as many as 450,000 people might have been affected by the condition since 2010, officials said.

Symptoms appear hours later

Unlike many allergic conditions that often show up quickly, symptoms for the red-meat allergy do not typically appear until two to six hours after eating, researchers and physicians said.

The typical case involves someone who has a big dinner that includes some version of red meat. “Often the fattier the meat, the more likely they’ll have a reaction,” said Scott Commins, an allergist and immunologist at the University of North Carolina at Chapel Hill.

“So hamburger or marbled steak are the kind of textbook thing, and they finish dinner, no symptoms, go on to bed and then are woken in the middle of the night with itching and hives and often gastrointestinal stress as well,” said Commins.

Exercise and alcohol worsen food allergies, he said. It’s not uncommon for people with severe reactions to report that they also had a glass or two of wine, and a bowl of ice cream, he said.

Advice: Ask a doctor: A tick bit me. What do I do now?

Since 2009, when scientists understood that the red-meat allergy was most likely caused by the bite of the lone star tick, health officials have become increasingly concerned about the growing number of suspected cases. But there’s limited knowledge of where and how many cases occur in the United States each year; alpha-gal syndrome condition is not required to be reported to health departments or the CDC.

It often takes multiple trips to doctors, including specialists, for people to get a proper diagnosis. That means additional hurdles for people to get diagnosed, said Johanna Salzer, a CDC epidemiologist who specializes in tick-borne diseases, highlighting a likely equity gap in treatment. Patients who sought testing were more likely to be White, with higher incomes and higher levels of education, according to research.

Low awareness among doctors

Awareness of the syndrome is low among health-care providers, according to the second CDC report. In a survey last year of 1,500 clinicians, 42 percent said they had not heard of the allergic condition; among those who had, fewer than a third knew how to diagnose it.

Commins, a co-author on both reports, said he has seen a significant increase in cases in recent years. “I’m now seeing eight to 10 newly diagnosed patients a week,” he said. He attributed the rise in cases to growing awareness among patients and the expanding range of the lone star tick.

The latest estimate of 450,000 people with red-meat allergy is likely an undercount, Commins said. Even if 450,000 is accurate, “that’s going to place alpha-gal syndrome in the top 10 of food allergies in the United States,” he added.

Based on the laboratory testing data, researchers found suspected cases predominantly in areas where the lone star tick is known to be established or has been reported — in the South, Midwest and Mid-Atlantic region, particularly Arkansas, Kentucky and Missouri.

The highest numbers of suspected cases were identified in New York and Virginia; Suffolk County, N.Y., alone accounted for 4 percent of all suspected cases nationwide, the CDC said.

“Apparently the lone star tick population there just exploded,” Commins said.