A recent study published in Emerging Infectious Diseases has shed new light on the role of black-legged ticks (Ixodes scapularis) in triggering alpha-gal syndrome (AGS), a condition that causes severe allergic reactions to mammalian meat. Researchers from the Centers for Disease Control and Prevention (CDC), the Maine Center for Disease Control and Prevention (Maine CDC), the University of North Carolina, and other institutions reviewed case studies spanning nearly a decade, revealing that black-legged ticks may be responsible for the condition, highlighting the need for broader awareness and enhanced surveillance.
Background: Understanding Alpha-Gal Syndrome
Alpha-gal syndrome, often called “mammalian meat allergy” or “tick bite meat allergy,” is a hypersensitivity reaction to a carbohydrate called galactose-α-1,3-galactose (α-gal), which is found in most mammalian meat products, such as beef, pork, and lamb. The allergic reaction can include symptoms like hives, rash, nausea, vomiting, difficulty breathing, dizziness, severe stomach pain, and, in extreme cases, anaphylaxis.
AGS is traditionally associated with bites from the lone star tick (Amblyomma americanum), which is particularly prevalent in the southeastern United States. However, this new study suggests that other ticks, including Ixodes scapularis, the black-legged tick, may also cause the syndrome, broadening the geographic range of AGS.
The Study: Case of a 45-Year-Old Woman in Maine
The study, conducted by Maine CDC, investigates the case of a 45-year-old woman who developed AGS-like symptoms after being bitten by a black-legged tick in York County, Maine, in May 2022. The patient reported the discovery of an adult female Ixodes scapularis tick on her left bicep, which was confirmed by the CDC through molecular and morphological analysis.
Nine days after the bite, the patient experienced severe gastrointestinal symptoms—abdominal pain and malaise—following the consumption of roasted rabbit. Over the next two weeks, she continued to have similar reactions after eating mammalian meat, with the symptoms worsening after consuming beef.
Despite no history of allergies or previous tick bites, the patient sought medical attention 20 days after the bite due to severe diarrhea and vomiting following beef consumption. Tests revealed an elevated α-gal–specific IgE level, confirming a diagnosis of AGS. However, unlike typical AGS cases, the patient did not show respiratory distress or anaphylaxis. Her symptoms were primarily gastrointestinal, indicating a different manifestation of AGS.
Further testing showed that the patient’s α-gal–specific IgE levels decreased over time, eventually reaching a low level after 25 months, suggesting a possible improvement in her condition. Despite this, her gastrointestinal symptoms were triggered several months after the initial tick bite, underscoring the long-term nature of the disease.
Progression of Symptoms: Bite Site Reaction and Follow-Up
The study also documented the progression of the bite site reaction, with the patient experiencing intense pruritus (itching) and erythema (redness) in the days following the tick bite. Over the next few months, the bite site healed, but the patient continued to experience intermittent flare-ups, which were gradually reduced by the 57th day after the bite. By December 2024, the bite site had resolved into an asymptomatic papule.
The study also tracked the patient’s progress after reintroducing red meat into her diet. Initially, consumption of bacon and steak triggered delayed heartburn sensations, but after several months, the patient was able to tolerate red meat without significant symptoms, showing a potential for remission of AGS in some cases.
Study Findings and Expanded Surveillance
This case study led the researchers to review the medical records of 57 Maine residents who reported symptoms similar to AGS between 2014 and 2023. Of these individuals, 23 tested positive for α-gal–specific IgE antibodies, confirming the presence of AGS. Interviews with the patients revealed exposure to various tick species, including the lone star, black-legged, and other ticks. However, not all exposures could be directly linked to the onset of AGS, suggesting that multiple tick bites or prior sensitization might contribute to the development of the syndrome.
The findings of the study indicate that black-legged ticks, which are found throughout much of the northeastern, midwestern, and northwestern United States, may be more involved in AGS than previously thought. This discovery expands the potential geographic range of AGS, which was once thought to be limited to areas inhabited by the lone star tick.
Conclusion: Implications for Healthcare and Surveillance
The study’s results suggest that non-lone star ticks, particularly the black-legged tick, can cause AGS, broadening the risk of the condition to more regions across the United States. In response, the CDC has increased surveillance and is encouraging healthcare professionals to be vigilant about tick bites and to screen patients for α-gal–specific IgE levels, particularly in areas where tick exposure is common.
As awareness of AGS grows, individuals who experience symptoms of the condition—particularly after tick bites—should seek medical advice and be tested for the presence of α-gal antibodies. Early diagnosis and management can help prevent the recurrence of allergic reactions and improve the quality of life for affected individuals.
The study also highlights the importance of considering all tick species, not just the lone star tick, in the monitoring and prevention of AGS. With increased surveillance and better awareness among clinicians and the public, it may be possible to reduce the incidence of AGS and ensure timely treatment for those affected.
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