Meat allergy from tick bites is on the rise—and US doctors are in the dark

A growing problem

The urgency to raise awareness of the condition was underscored in the second study, which looked at the prevalence and distribution of AGS cases in the US. Researchers collected alpha-gal–specific IgE (sIgE) antibody testing results between 2017 and 2022. They got the test results from the commercial lab testing company Eurofins Viracor, which, until 2022, conducted nearly all alpha-gal–specific IgE tests in the country. As such, they had testing results on over 295,000 people from all over the US.

Overall, 90,018 (30.5 percent) were positive for the antibody, meaning they likely had AGS. Throughout the studied time period, the percentage of people getting positive tests stayed around 30 percent. But each year, the number of people getting tested increased. This resulted in the number of new suspected cases increasing by about 15,000 each year between 2017 and 2022.

When the researchers combined the 90,018 suspected cases from 2017 to 2022 with suspected cases between 2010 and 2018, they came to a total of 110,229 suspected cases in the 2010 to 2022 period after AGS's discovery. Then they did some simple math to estimate the true number of cases that may be out there:

Assuming 70 percent–90 percent of these suspected cases (77,161–99,207) are clinically compatible AGS cases, and assuming that 22 percent–80 percent of all persons with AGS have access to knowledgeable [health care providers] who submit a specimen for alpha-gal sIgE testing, 96,000–450,000 persons in the United States might have been affected by AGS since 2010.

The researchers also used geographic data linked to test results to determine where the cases were occurring. Unsurprisingly, the cases clustered in areas where the lone star tick is known to be established—though other ticks and potentially chiggers have also been linked to AGS. For now, the high-prevalence regions included parts of Oklahoma, Kansas, Arkansas, Missouri, Mississippi, Tennessee, Kentucky, Illinois, Indiana, North Carolina, Virginia, Maryland, and Delaware.

"The burden of alpha-gal syndrome in the United States could be substantial given the large percentage of cases suspected to be going undiagnosed due to non-specific and inconsistent symptoms, challenges seeking healthcare, and lack of clinician awareness," Dr. Johanna Salzer, a CDC researcher and senior author on both papers released today, said in a statement. "It’s important that people who think they may suffer from AGS see their healthcare provider or an allergist, provide a detailed history of symptoms, get a physical examination, and a blood test that looks for specific antibodies (proteins made by your immune system) to alpha-gal."

The CDC notes that people who have AGS can have wide-ranging experiences, including hives or itchy rash; nausea or vomiting; heartburn or indigestion; diarrhea; cough; shortness of breath or difficulty breathing; drop in blood pressure; swelling of the lips, throat, tongue, or eyelids; dizziness or faintness; or severe stomach pain.

Symptoms often appear two to six hours after eating alpha-gal-containing food or having another type of exposure to the carbohydrate (e.g., gelatin-coated medications). The several-hour delay in an allergic reaction after exposure is unique to AGE among food allergies, which usually occur within minutes to two hours. This can make it harder for people with AGS to identify foods as the trigger of their symptoms. It's unclear what's behind the delay, but it's thought that alpha-gal may have slower digestion and absorption than other allergens.

There is no cure or treatment for AGS other than avoiding alpha-gal. For those with severe allergic reactions, common medications like epinephrine are used for treatment.