Where Alpha-Gal Syndrome Shows Up Mapping a Tick-Driven Allergy Across the U.S. and Beyond

The geographic story of alpha-gal syndrome began with a clinical puzzle in the American South. Doctors noticed that "a subset of patients in US southern states had allergic reactions to the anti-cancer monoclonal antibody cetuximab at rates 20-fold higher than observed during clinical trials using cetuximab in other US regions, like the northeast or the west coast" (PMC 2025). In plain terms: a single cancer drug, cetuximab, was triggering severe allergic reactions in southern patients about 20 times more often than in patients on either coast. That regional disparity — a severe drug reaction concentrated in a specific part of the country — became the first thread in unraveling a condition now reported on nearly every continent.

Alpha-gal syndrome (AGS) is "an emerging, tick bite–associated allergic condition characterized by potentially life-threatening hypersensitivity to an oligosaccharide found in most mammalian meat and products derived from it" (CDC 2023). The oligosaccharide in question is a sugar called alpha-gal, found in beef, pork, lamb, and other mammalian products. For a fuller introduction to what AGS is and how the alpha-gal sugar triggers the immune response, see Alpha-Gal Syndrome: What It Is and Why It Matters. This article focuses on a different question: where.

"Allergic reactions to alpha-gal were first described by Chung et al. Their report grew from observations that cancer patients living in the Southeastern US experienced significantly more anaphylactic reactions than patients in New England, California, or Europe following initial intravenous doses of cetuximab, a monoclonal antibody and cancer chemotherapeutic agent. Chung and colleagues found that IgE antibodies specific for galactose-alpha-1,3-galactose glycosylating the monoclonal antibody were critical for the development of these immediate hypersensitivity responses." — PMC, 2020. "Doc, Will I Ever Eat St...

Early case series soon followed from the southeastern United States and Australia, establishing a pattern: "Both groups also reported that history of tick bite was common to all these patients." (PMC 2020)

Where in the U.S. Is Alpha-Gal Syndrome Most Common?

The most comprehensive look at AGS geography in the United States comes from a CDC analysis of laboratory data — testing records from hundreds of thousands of people whose blood was checked for alpha-gal allergy. "Among 233,521 persons for whom geographic data were available, suspected cases predominantly occurred in counties within the southern, midwestern, and mid-Atlantic U.S. Census Bureau regions." (CDC 2023) The CDC identified a near-contiguous corridor of high prevalence: "The highest prevalences of suspected cases (per 1M PPY) were found throughout a nearly contiguous region of the southern, midwestern, and mid-Atlantic United States, particularly parts of Oklahoma, Kansas, Arkansas, Missouri, Mississippi, Tennessee, Kentucky, Illinois, Indiana, North Carolina, Virginia, Maryland, and Delaware." (CDC 2023) The unit "per 1M PPY" — per one million person-years — is a way of comparing rates across places with different population sizes, and it shows AGS forming a thick band of cases stretching from Oklahoma to the Atlantic.

At the county level, the data reveal striking hotspots. "The highest numbers of suspected AGS cases were identified in counties within New York (Suffolk ) and Virginia (Bedford ); 4% of all suspected cases nationwide resided in Suffolk County, New York." (CDC 2023) In other words, one suburban Long Island county alone accounted for roughly 1 in every 25 suspected cases in the country. The highest rates per capita, meanwhile, fell in rural counties in Virginia and Kentucky: "The highest number of suspected AGS cases per 1M PPY were in counties in Virginia (Charlotte ) and Kentucky (Muhlenberg )." (CDC 2023)

"Persons with suspected AGS were predominantly located in areas where the lone star tick is known to be established or reported, particularly throughout Arkansas, Kentucky, Missouri, and Suffolk County, New York." — CDC, 2023. Geographic Distribution o...

That geographic pattern closely tracks the range of the lone star tick (Amblyomma americanum) — a small, aggressive tick named for the white spot on the female's back. "Suspected AGS cases were predominantly located in areas where the lone star tick (Amblyomma americanum) is known to be established or reported." (CDC 2023) The CDC reference manual describes that range as spanning "from central Texas and Oklahoma eastward across the southern states and along the Atlantic Coast as far north as Maine" (CDC 2022). The map of where lone star ticks live and the map of where AGS cases cluster are, in practice, the same map. For a detailed profile of the lone star tick itself, see Lone Star Tick (Amblyomma americanum).

One of the more striking geographic overlaps involves another lone-star-transmitted disease. "The geographic distribution of AGS is very similar to that of ehrlichiosis, caused by Ehrlichia chaffeensis and E. ewingii, disease agents also known to be transmitted by the lone star tick. These data therefore support the association previously observed between lone star ticks and alpha-gal sensitization among patients in the United States." (CDC 2023) Ehrlichiosis is a bacterial infection spread by the same tick that's linked to AGS, so seeing the two conditions clustered in the same counties is strong circumstantial evidence that lone star ticks are doing the work.

Sensitization rates in high-exposure populations

Within the areas most affected, sensitization to alpha-gal is far more common than clinical AGS. "In certain geographic areas and in populations with high tick exposure, the level of sensitization can be 15-35% but this does not represent clinical AGS, which appears to occur in 1-8% of sensitized individuals." (T&F 2020) "Sensitization" here means the immune system has produced alpha-gal allergy antibodies — a blood-test signal — without necessarily causing reactions when the person eats meat. Specific studies put numbers to this gap: in North Carolina, "the sensitization rate (positive to alpha-gal sIgE) was found to be 22% among a cohort of patients undergoing endoscopy without a history of AGS in North Carolina, while an asymptomatic cohort in Tennessee showed a sensitization rate of 20.8%." (CDC 2022) sIgE — specific IgE — is the allergy antibody aimed at one target, in this case alpha-gal. Roughly one in five people tested in those studies carried the antibody, even though most had no symptoms.

A larger laboratory-based picture confirmed broad sensitization. "Recently, a study incorporating 122,068 serum samples from >100,000 unique patients in the United States demonstrated an alpha-gal IgE sensitization rate of 32.4%. The states with the highest numbers included Arkansas, Virginia, Kentucky, Oklahoma, and Missouri." (PMC 2022) About a third of more than 100,000 blood samples — drawn from patients whose doctors thought there was a reason to test them — came back positive for alpha-gal antibodies.

Rural populations bear a disproportionate burden. "Rural dwelling individuals have higher rates of sensitization than urban with a strong association between development of alpha-gal sIgE and clinical AGS with tick bite history." (PMC 2025) A study of military recruits illustrated how geography and occupation intersect: "In a cohort of 3,000 military recruits reporting for intake to 1 of 10 military bases in the central and eastern United States, the incidence of AGS was 6%. Military recruits from Arkansas, Oklahoma, and Missouri had the highest incidence. Rural residence, male sex, and White race were also associated with sensitization, meaning that individuals from these groups were more likely to develop an immune response to the molecule, which can lead to allergic reactions upon subsequent exposures." (HHS 2024) Six percent of 3,000 incoming recruits — roughly 180 young adults — already showed signs of AGS by the time they reached basic training.

Outdoor workers face particularly high exposure. "A German study identified a 2.5-fold higher rate of α-Gal sensitization in forest service employees compared with a residential population." (AHA 2022) Forest workers spend their days in tick habitat; ordinary residents do not. The 2.5-fold gap suggests time outdoors in tick country is a major driver of who becomes sensitized. For a broader look at who is at highest risk based on activity and region, see Tick Risk by Geography.

The scale of the problem

The numbers are large and growing. The HHS Tick-Borne Disease Working Group reported that "In 2009, there were 24 reported cases of AGS; however, more recent data documented more than34,000 cases from 2010 to 2018 in the United States alone, and AGS was identified as the leading cause of anaphylaxis in a southeastern registry of patients. Thus, AGS likely represents the second most common cause of tick-borne illness behind only Lyme disease." (HHS 2022) The jump from 24 reported cases in 2009 to more than 34,000 in the following decade is roughly a thousandfold increase. Anaphylaxis, the severe whole-body allergic reaction the quote refers to, can drop blood pressure and close the airway within minutes.

Between 2017 and 2022, the CDC's laboratory surveillance showed continued escalation. "Overall, 90,018 (30.5%) persons received a positive test result in the study period, and the number of persons with positive test results increased from 13,371 in 2017 to 18,885 in 2021." (CDC 2023) But these numbers almost certainly represent a fraction of actual cases:

"Assuming 70%–90% of these suspected cases (77,161–99,207) are clinically compatible AGS cases, and assuming that 22%–80% of all persons with AGS have access to knowledgeable HCPs 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." — CDC, 2023. Geographic Distribution o...

That estimate — potentially hundreds of thousands of affected individuals — underscores a condition the HHS described as largely invisible to the public health system: "The magnitude of the problem and the true number of cases of alpha-gal allergy is unknown. There is very little awareness of alpha-gal allergy, and it is not a reportable disease." (HHS 2018) A "reportable disease" is one doctors are required by law to notify health authorities about; AGS is not on that list, so cases go uncounted.

Cases appearing outside the lone star tick's established range

The geographic picture is not confined to the lone star tick's traditional territory. The CDC analysis found "Counties with moderate and high numbers of suspected cases per 1M PPY were detected in Minnesota and Wisconsin, corresponding to 238 total suspected cases (238 of 2,456 persons tested; 9.7%) during the 6-year study period, and were distinct from this contiguous region." (CDC 2023) A study from the upper Midwest added detail: "A small retrospective review in Iowa, Minnesota, and Wisconsin found that of 47 AGS patients who received positive alpha-gal sIgE test results, 11 (23%) lived in areas where the lone star tick was not previously known to be present, and some persons reported bites from blacklegged ticks (four; 9%) or lone star ticks (three; 6%), although when these bites occurred relative to symptom onset or how the ticks were identified is not described (7)." (CDC 2023) The blacklegged tick (Ixodes scapularis), best known as the carrier of Lyme disease in the Northeast and Midwest, is a different species from the lone star tick — and its appearance in this data hints that AGS may not be a one-tick story.

A 2025 study from Maine sharpened this finding with a specific case. Researchers "investigated a patient with confirmed AGS in Maine, USA, showing symptoms 9 days after a blacklegged tick (I. scapularis) bite" (CDC-EID 2025). Maine's surveillance data revealed a modest but growing footprint: "Maine CDC received positive α-gal–specific IgE laboratory reports spanning November 2014–October 2023 for 57 Maine residents" (CDC-EID 2025). In Maine, the lone star tick is not established — "The lone star tick is not believed to be established in Maine, currently, though populations are moving up the east coast and are established in southern Massachusetts." (MaineCDC 2023)

The CDC weighed in carefully on what the out-of-range cases mean: "In this investigation, the geography suggests that lone star ticks remain the primary species associated with AGS in the United States, and cases outside the established range of this tick species need to be further investigated to better understand exposure history and contributing factors associated with the onset of this allergic condition." (CDC 2023) Other tick species cannot be ruled out. As a 2025 CDC report noted, "Other global tick species cause AGS in humans; other human-biting ticks in the United States may play a role in α-gal sensitization." (CDC-EID 2025) For the biological mechanisms behind how different tick species may trigger sensitization, see How Tick Bites Trigger Alpha-Gal Sensitization.

The CDC also flagged a practical concern about case geography: "localities associated with patient test results do not necessarily reflect the geographic area where the tick bites or first onset of AGS symptoms occurred, and travel-associated cases certainly are possible." (CDC 2023) A patient tested in Maine may have been bitten in Virginia six months earlier; the test record reflects where care happened, not where the tick was.

The lone star tick's expanding range and what it means for AGS

The lone star tick's range is not static. "The geographic range of the Lone Star tick covers primarily the southeastern and midwestern area of the U.S. but is expanding northward and even into Canada." (PMC 2025) This expansion has direct consequences for AGS: "The incidence of AGS is increasing in the southwest and eastern coastal regions of the United States, which correlates with the expansion and distribution of the Lone Star tick." (FrontCellInfectMicrobiol 2021) As the tick moves into new territory, AGS tends to follow.

"Climate change has been implicated in the expansion of the Lone Star tick, allowing a larger endemic range, increased tick populations, and longer active periods." — PMC, 2025. Alpha-gal syndrome and th...

A 2025 review found evidence that the ticks may be adapting to colder environments: "In addition, lone star ticks can lay thousands of eggs at a time, which facilitates their spread. A study of lone star ticks in New York identified genetic differences that may suggest adaptation conferring resistance to the northern climate." (PMC 2025) High reproductive output plus signs of cold-tolerance evolution helps explain how a southern tick is establishing further north each decade. For a deeper look at how climate change is driving tick range shifts across species, see Climate Change and Tick Range Expansion.

The CDC concluded its geographic analysis with a forward-looking warning:

"If testing trends continue, and the geographic range of the lone star tick continues to expand, the number of AGS cases in the United States is predicted to increase during the coming years, presenting a critical need for synergistic public health activities including 1) community education targeting tick bite prevention to reduce the risk for acquiring AGS, 2) HCP education to improve timely diagnosis and management, and 3) improved surveillance to aid public health decision-making." — CDC, 2023. Geographic Distribution o...

AGS beyond the United States

The global picture reinforces that AGS is not an American phenomenon. "Alpha-gal syndrome cases arising after hard-bodied tick bites have been reported on every continent except Antarctica." (PMC 2022) Hard-bodied ticks are the family of ticks with a stiff plate on the back — the kind most people picture when they think "tick" — as opposed to the softer, less common soft-bodied ticks. Different species are implicated across regions: "Tick species such as Ixodes ricinus in Europe, Amblyomma americanum in North America, Haemaphysalis longicornis in Asia and Ixodes holocyclus in Australia are linked to AGS, currently considered an emergent life-threatening allergy in tick endemic areas worldwide." (PMC 2022) In plain English: each continent has its own tick — Ixodes ricinus (the castor bean tick) in Europe, the lone star in North America, Haemaphysalis longicornis (the Asian longhorned tick) across Asia, and Ixodes holocyclus (the Australian paralysis tick) Down Under — and AGS shows up wherever those ticks live in numbers.

Regional patterns vary. In Sweden, the condition follows the range of Ixodes ricinus: "α-Gal syndrome is relatively common in Southern Sweden where Ixodes ricinus is endemic, however, there are no reports of α-Gal sensitization in Northern Sweden where Ixodes ricinus is not found." (AHA 2022) Same country, two different tick situations, two different rates of AGS. In Australia, AGS cases cluster along the coast where Ixodes holocyclus lives: "In Australia, including the south coast of New South Wales and Sydney coast, AGS cases coinciding with the endemic area inhabited by the Ixodes holocyclus tick have been reported." (FrontCellInfectMicrobiol 2021) Researchers have noted that "Australia is among the countries with the highest AGS and anaphylaxis rates in the world." (FrontCellInfectMicrobiol 2021)

Further afield, "AGS cases in Korea are also believed to be associated with H. longicornis tick bites" (FrontCellInfectMicrobiol 2021) — the Asian longhorned tick — while in Central America, "the tick species belonging to A. cajennese complex, prevalent in Costa Rica and neighboring countries, are thought to be involved in causing AGS." (FrontCellInfectMicrobiol 2021)

Some regions present a puzzle. African populations show widespread sensitization but little clinical disease. "Interestingly, numerous African countries that conducted seroprevalence studies found that individuals have IgE antibodies specific to α-gal. However, there was no indication of any allergic reactions after red meat consumption." (FrontCellInfectMicrobiol 2021) Seroprevalence studies measure how many people in a population carry a particular antibody in their blood; in African studies, alpha-gal antibodies were common, yet meat-allergy reactions were not — a disconnect researchers are still trying to explain. In South Africa, a small number of clinical cases have appeared, but "the patients with AGS recalled having a tick bite before the onset of AGS symptoms, although the tick species has yet to be determined." (FrontCellInfectMicrobiol 2021) One explanation may lie beyond ticks entirely: "The most compelling non–tick bite factor that may contribute to AGS development is exposure to the helminth Ascaris lumbricoides. Murangi et al found that high Ascaris IgE levels correlated more strongly with AGS than did tick bites in Africa." (PMC 2025) A helminth is a parasitic worm; Ascaris lumbricoides is the giant intestinal roundworm, common in places with limited sanitation, and the paper above suggests it — not a tick — may be doing the sensitizing in parts of Africa.

The surveillance gap

Across all of these geographies, a fundamental problem persists: AGS remains invisible to most public health systems. It is "not nationally reportable" (HHS 2024) in the United States, and "Whether the increasing numbers of suspected AGS cases seen in this study are an indication of increased awareness, increasing emergence, or both remains unclear." (CDC 2023) Translation: case counts are climbing, but no one can yet say how much of the rise is more people getting AGS versus more doctors learning to test for it.

Healthcare provider knowledge gaps compound the problem. A CDC survey found that "Limited HCP knowledge about AGS is concerning, especially because the number of suspected cases is increasing, and the range of the tick primarily associated with this condition is expected to expand." (CDC 2023) HCP stands for healthcare provider — doctors, nurse practitioners, and physician assistants who would be the ones recognizing AGS in clinic. Even in the regions most affected, clinician awareness was low: "Knowledge scores were similar across U.S. Census Bureau regions (p = 0.44), and number of years in practice was not significantly associated with provider knowledge scores." (CDC 2023) Working in a high-AGS state did not, on its own, make doctors more familiar with the condition.

Clinicians in tick-endemic areas have been urged to keep AGS in mind for unexplained symptoms. As one review recommended, "We suggest testing for alpha-gal IgE in tick-endemic areas as part of the evaluation for cases of idiopathic anaphylaxis, recurrent urticaria and/or angioedema, as well as recurrent, episodic gastrointestinal cramping of unestablished cause." (T&F 2020) Idiopathic means "of unknown cause"; urticaria is hives; angioedema is swelling under the skin. The recommendation is that when those reactions show up without an obvious trigger in tick country, alpha-gal belongs on the test list. A study of previously unexplained anaphylaxis cases drove the point home: "A study from the National Institutes of Health, found 9% of subjects diagnosed with idiopathic anaphylaxis had circulating, detectable alpha-gal-specific IgE (≥0.35 kU/L), reported a tick bite history, and resided within the Southeastern and Mid-Atlantic US where lone star ticks also live." (PMC 2020) Almost one in ten patients whose severe allergic reactions had no known cause turned out to have alpha-gal antibodies and a tick bite in their history.

"In summary, this report demonstrates that AGS is both a severe allergy, with nearly 75% of patients meeting criteria for anaphylaxis, and also distinct from other food allergies in its symptom profile. With tick bites common across most of the United States and other regions of the world, a substantial number of people are at risk for developing this potentially fatal disease. Yet, many providers are not aware of the condition, and patients may suffer for years before an accurate diagnosis." — CDC, 2022. Clinical and laboratory f...

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