tick insect warning sign in forest
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New data from the CDC suggests that alpha-gal syndrome—a tick-borne allergy to red meat—may be more widespread than previously thought.
Scientists long believed that only the lone star tick was responsible for the condition, but two new studies suggest that blacklegged (deer) ticks may also cause it.
Experts recommend taking precautions to avoid tick bites and considering the condition if you have an unexplained allergic reaction.
Alpha-gal syndrome (AGS)—an allergic condition to red meat caused by tick bites—is becoming increasingly prevalent in the U.S.1 Now, new data suggests more varieties of ticks can trigger AGS than originally suspected.
Scientists have long believed that the lone star tick (Amblyomma americanum), which lives in the Eastern, Southeastern, and South-Central United States, is solely responsible for AGS.2
However, two new studies from the Centers for Disease Control and Prevention (CDC) identified multiple people who developed AGS after being bitten by blacklegged ticks (also called deer ticks).34
Estimates suggest up to 450,000 Americans have been affected by AGS between 2010 and 2022.1
“These findings broaden our understanding of where alpha-gal syndrome may occur and who’s at risk, which could improve diagnosis and increase awareness among healthcare providers in regions previously thought to be low-risk, such as Maine,” Bobbi Pritt, MD, pathologist and clinical microbiologist at the Mayo Clinic and spokesperson for the College of American Pathologists, told Health.
What Is Alpha-Gal Syndrome?
AGS develops when a tick bites someone and passes alpha-gal—a carbohydrate found in all non-primate mammals—into the bloodstream, explained Ryan Steele, DO, allergist-immunologist at Yale Medicine and assistant professor of clinical medicine at the Yale School of Medicine.
Once alpha-gal is in the blood, the immune system produces an antibody called immunoglobulin E (IgE) in response.5
So the next time a person consumes or is exposed to the alpha-gal carbohydrate, those IgE antibodies can trigger symptoms of an allergic reaction, including hives, stomach pain, a drop in blood pressure, and in severe cases, anaphylaxis.5 According to Britt, the reaction is often delayed, showing up two to six hours after eating.
“When that person eats red meat—like beef, pork, venison, or lamb—or is exposed to other mammal-derived products like gelatin or dairy, [or] some medications, their immune system recognizes the alpha-gal in those products and overreacts,” explained Pritt.
These allergic symptoms—combined with a history of tick bites and a positive blood test for IgE—lead to a diagnosis. Over time, some patients’ IgE levels go down and they’re able to eat meat and dairy products again, Pritt added. But subsequent tick bites can reactivate the reaction.
Women in Oregon and Maine Developed AGS From Blacklegged Ticks
The first CDC case study evaluated the emergence of AGS in a 61-year-old woman in Oregon. In the spring of 2017, the woman sought care after experiencing severe symptoms of an allergic reaction, including skin rash, itchiness, tongue swelling, throat tightness, and wheezing.4
A month before the episode, the woman had noticed a tick latched onto her shoulder after walking in the woods with her dog.4
So what caused her allergic reaction? Beef tacos, pork sausage, and a ham sandwich were to blame, doctors discovered. She tested positive for IgE antibodies and was diagnosed with AGS.4
In April 2020 and again in March 2022, the woman was bitten by Ixodes pacificus ticks—or western blacklegged (deer) ticks. Testing revealed the bites caused her IgE antibody levels to soar, suggesting that this species of tick can also cause AGS, particularly after repeated bites.4
The second CDC case study looked at a 45-year-old woman in Maine who found a tick attached to her leg after walking on a trail in May 2022. It was an Ixodes scapularis tick, another species of blacklegged or deer tick.3
In the weeks following her bite, the woman experienced stomach pain, diarrhea, and vomiting after eating various kinds of red meat.3
Testing revealed the woman had abnormally high levels of IgE. She was advised to avoid beef, pork, and lamb, and had to stop eating some dairy products. Over the course of a year, the woman's IgE levels gradually dropped, and eventually she could eat meat again.3
Some people with AGS develop allergy symptoms, such as the Oregon woman, but the syndrome manifests with gastrointestinal symptoms for other people.3
“These case reports highlight that patients in areas outside the established range of the lone star tick may also be at risk, although the evidence continues to support that in the U.S., most alpha-gal syndrome patients develop the allergy after experiencing a bite from a lone star tick,” one of the study’s co-authors, Johanna Salzer, DVM, PhD, veterinary medical officer and epidemiologist with the CDC’s Division of Vector-Borne Diseases, told Health.
The Maine CDC boosted its surveillance of AGS back in 2023. They identified 57 Maine residents who tested positive for IgE between November 2014 and October 2023.3
AGS May Be More Widespread Than Previously Suspected
The two reports suggest that various types of blacklegged tick species across the U.S. could cause AGS—meaning that more Americans should be on the lookout for symptoms of the syndrome.
“AGS is primarily caused by the bites of lone star ticks,” Salzer emphasized. “But it is possible that other ticks in the U.S. play a role in causing AGS in some people.”
Traditionally, most cases of AGS have been reported in states such as Missouri, Arkansas, Tennessee, Kentucky, Virginia, and North Carolina, among other states in the Mid-Atlantic, Southeast, South-Central, and Midwest regions.1
But I. pacificus ticks, which appear to have caused AGS in the woman from Oregon, live along the Pacific Coast in California, Oregon, and Washington. These ticks have been linked to AGS cases in Australia and Europe, but hadn’t been previously associated with AGS in the U.S.4
And I. scapularis ticks, which raised the Maine woman’s IgE levels, are commonly found in the Upper Midwest, the East Coast, and the South.6
This means regions once considered to be low-risk for AGS—including Maine and Oregon—may actually contain plenty of ticks that can cause AGS.61
“These findings help to support the idea that the geographic distribution and species of ticks that carry alpha-gal are more widespread than we have found in the past,” said Steele.
Protecting Yourself Against AGS and Tick Bites
Though scientists are making strides, there’s still a lot we don’t know about AGS—that includes why lone star ticks appear to cause the majority of cases as compared to blacklegged ticks, said Salzer. Ongoing studies are also looking into other potential causes of AGS, from parasites to infections to vaccines, Pritt said.
But as of now, “tick bites are the main and best-supported cause,” she said.
So, what’s the most effective way to avoid getting AGS? Don’t get bitten by a tick.7
You can minimize your chances of being bitten by a tick by doing the following, Salzer advised:
Using bug repellents recommended by the Environmental Protection Agency
Wearing specially treated permethrin clothing
Checking yourself for ticks (and promptly removing them) after you spend time in wooded or grassy areas
It’s crucial to check your pets, too. “They can acquire tick-borne diseases such as Lyme disease, and can also bring ticks into the house,” Pritt said.
According to Steele, the findings should encourage physicians and patients alike to always consider AGS if they have an unexplained allergic reaction to meat or dairy products, even if they live in an area where AGS is thought to be rare.
“Healthcare providers and public health professionals in regions with lone star ticks, blacklegged ticks, and western blacklegged ticks should be aware of AGS and be able to recognize symptoms,” said Salzer.