Tick-linked meat allergy marker appears common in parts of the US
A CDC-published study found alpha-gal antibodies in up to about 31% of blood donors in some states, far above diagnosed allergy estimates.
By Hana Yoshida · Markets Reporter
3 min read
A blood marker tied to a tick-associated red meat allergy appears far more common in some U.S. states than the allergy itself, according to a study published in the CDC’s Morbidity and Mortality Weekly Report. The finding could complicate diagnosis of alpha-gal syndrome, a condition that can cause delayed allergic reactions after people eat red meat or other mammal-derived products.
The CDC has previously estimated that up to 450,000 people, or about 0.14% of the U.S. population, have alpha-gal syndrome. The new study found much higher rates of alpha-gal IgE antibodies in blood donations from several states where the lone star tick is established, suggesting many people may carry the antibody without clear symptoms.
What the antibody means
Alpha-gal syndrome is linked to an immune response against galactose-α-1,3-galactose, often called alpha-gal. The molecule is found in nonprimate mammals such as cows and pigs and can also be present in tick saliva, especially from the lone star tick, according to the CDC-published report.
After a tick bite, some people develop IgE antibodies against alpha-gal. In some cases, those antibodies are associated with allergic reactions after eating red meat or consuming other animal-derived products, including dairy and gelatin.
The condition is difficult to recognize because symptoms often begin two to six hours after a meal, according to CDC information cited in the report. Reactions can include hives, nausea, vomiting, abdominal cramps and diarrhea. Severe cases can involve anaphylaxis, with breathing problems, throat tightness, swelling of the tongue or lips, dizziness, a weak pulse or low blood pressure.
Researchers have known for years that alpha-gal antibodies do not always mean a person has meat allergy symptoms. The CDC-published report notes earlier findings involving cancer patients who reacted severely to cetuximab, a monoclonal antibody drug containing alpha-gal, in states where lone star ticks are present. Those patients had alpha-gal IgE antibodies but did not necessarily report reactions to eating meat.
Highest rates in lone star tick states
The new study was led by infectious disease researchers at the University of North Carolina at Chapel Hill, according to the report. The team tested 3,000 blood donation samples from 10 states, with 300 samples from each state, then used the results to estimate antibody prevalence.
Six states in the study are within established lone star tick range: Arkansas, Kentucky, Missouri, South Carolina, Tennessee and Virginia. Maine and Minnesota have some regions that may include the tick, while New Mexico and Washington are outside its range, according to the researchers.
Antibody prevalence was highest in states where the lone star tick is established. South Carolina had the lowest estimate among those six states, at 5.5%. The other five ranged from 21.5% in Tennessee to 31.2% in Arkansas, with a combined estimate of 24% across those five states.
Maine and Minnesota had estimated prevalence rates of 10.6% and 5.4%, respectively. New Mexico and Washington had the lowest estimates, at 1.9% and 1.1%.
Diagnosis still depends on symptoms
The researchers did not have information on whether the blood donors had been diagnosed with alpha-gal syndrome. They concluded that symptom-free sensitization to alpha-gal may be common, while the syndrome itself appears less common.
That gap matters for patients and clinicians. The researchers warned that relying only on a positive antibody test could lead to overdiagnosis and unnecessary dietary restrictions. CDC case definitions and clinical guidance say diagnosis should be tied to symptoms after eating red meat, and guidelines recommend a trial period avoiding meat to see whether symptoms improve.
Researchers said major questions remain, including what share of people with alpha-gal antibodies have the syndrome, whether some may develop symptoms later after additional tick bites, and whether the antibodies carry other health risks. The report said antibody surveillance could help identify high-prevalence areas for further study.
This story draws on original reporting from Ars Technica.