The Lone Star Tick (Amblyomma americanum) Aggressive Human Biter, Alpha-Gal Vector, and Expanding Its Range

The lone star tick is a southern animal on the move. The CDC's 2022 tickborne diseases reference manual describes it in plainer terms than most sources bother with — "A very aggressive tick that bites humans" (CDC 2022) — and the 2020 HHS Tick-Borne Disease Working Group's biology subcommittee opens its species entry by flagging why this tick has become a priority:

"The lone star tick (A. americanum) is a tick of increasing importance due to significantly expanding geographic range, increased population density, and roles as vector of established and emerging infectious agents that include E. chaffeensis, E. ewingii, and the recently described Heartland and Bourbon viruses. A. americanum is increasingly important medically due to its involvement in galactose-alpha-1, 3-galactose, or alpha-gal allergy, a significant cause of human allergies resulting from exposure to a number of allergens. Distribution of this important pest tick was historically described as the southeastern United States to west central Texas and north to Iowa; however, the geographic range now extends into the Mid-Atlantic States and New England, and is regularly detected as far north as Maine." — HHS, 2020. Tick Biology, Ecology, an...

That combination — expanding geographic range, rising population density, and a growing pathogen list — is why a tick that until recently was "a southern problem" now sits near the center of U.S. tick-borne disease ecology. Stafford's 2017 integrated pest management review captures the scale of the tick's dominance in its core territory: "The vast majority of ticks (>95%) removed from humans in southeastern states are A. americanum" (OUP 2017).

What does a lone star tick look like and what diseases does it carry?

The species name gives the field-identification marker. The 2007 Connecticut Agricultural Experiment Station tick management handbook — the canonical homeowner reference — opens its entry with the naming:

"The Lone Star Tick, Amblyomma americanum (L.) The lone star tick, Amblyomma americanum, is named from the conspicuous spot on the end of the scutum of the female tick. This tick is the vector for Ehrlichia chaffeensis, the agent of human monocyctic ehrlichiosis (HME). The tick does not transmit the Lyme disease bacterium, B. burgdorferi, but has been linked with a Lyme-like illness with a rash and other symptoms resembling Lyme disease called southern tick-associated rash illness or STARI." — CAES, 2007, pp. 19–20. Tick Management Handbook:...

The CDC reference manual adds the rest of the identification card: the adult female is "distinguished by a white dot or “lone star” on her back" (CDC 2022), and "The nymph and adult females most frequently bite humans" (CDC 2022). Behaviorally, the tick is a generalist — "The lone star tick has a wide host range, feeding on virtually any mammal. All stages will feed on people" (CAES 2007) — and the bite is not subtle: "The bite of this tick can be painful because of the long mouthparts and attached ticks can caused great irritation" (CAES 2007).

A 2025 CCDCW paper summarizes the species at the same level: it is "an aggressive three-host tick predominantly found in eastern North America, with particular prevalence in the south of the United States" (CCDC 2025).

The pathogen list

The roster of illnesses transmitted or associated with A. americanum is long and has been growing. The CDC reference manual's tick-ID card lists the confirmed agents:

"TRANSMITS Ehrlichia chaffeensis and E. ewingii (which cause human ehrlichiosis), Francisella tularensis (tularemia), Heartland virus (Heartland virus disease), Bourbon virus (Bourbon virus disease), and Southern tick-associated rash illness (STARI)." — CDC, 2022, pp. 3–4. Tickborne Diseases of the...

The 2020 HHS biology subcommittee gives the longer working list, including associations where vector competence is still being established:

"Lone star tick (A. americanum). This species is the primary vector of multiple pathogens causing ehrlichiosis (E. chaffeensis, Ehrlichia ewingii, and Panola Mountain Ehrlichia) and has also been implicated as the vector for Heartland virus; and Bourbon virus. The lone star tick also was implicated as the vector of Borrelia lonestari, the putative agent of southern tick associated rash illness (STARI); and was linked to a delayed allergic reaction to a number of different allergens, also known as the alpha gal allergy, which is becoming increasingly recognized as a health problem throughout this tick's range. Lone star ticks have also been associated with the agents of Rocky Mountain spotted fever (RMSF), tularemia, and Q fever, and their bite may induce tick paralysis. Except for the RMSF agent, the vector competence of lone star ticks for these disease agents remains unproven. With increasing abundance in its “native” range in the southeastern United States and geographic expansion northward, control of this aggressive tick has become increasingly important." — HHS, 2020. Tick Biology, Ecology, an...

Ehrlichiosis. The lone star tick is the primary U.S. vector of human ehrlichiosis. A 2019 ASM review on emerging tick-borne diseases: "E. chaffeensis is a zoonotic tick-borne pathogen transmitted by infected Amblyomma americanum ticks" (ASM 2019), and "E. chaffeensis is the most common species of Ehrlichia to infect humans" (ASM 2019). A second species, E. ewingii, has the same vector — "E. ewingii is an emerging Ehrlichia species that infects humans and is transmitted by infected larval and nymphal A. americanum ticks" (ASM 2019). The 2022 HHS ecology subcommittee underscores how central the tick is to the ehrlichiosis picture — it is "the primary vector for the largely under-recognized and under-reported ehrlichioses (E. chaffeensis and E. ewingii)" (HHS 2022). For a full clinical and geographic account of ehrlichiosis, see Ehrlichiosis and the Lone Star Tick's Geography.

Heartland and Bourbon viruses. Two more recently recognized viruses share the same vector. The 2019 ASM review on HRTV: "The predominant vector of HRTV appears to be Amblyomma americanum, the Lone Star tick. Transmission can occur transstadially from one stage to the next, vertically from adult to offspring, and by cofeeding infection" (ASM 2019). For Bourbon virus: "The vector of BRBV is thought to be Amblyomma americanum (L.) ticks on the basis of virus isolation from three pools of adults and nymphs in northwestern Missouri at a location near Bourbon County, KS" (ASM 2019).

Southern Tick-Associated Rash Illness (STARI). A bite from A. americanum can produce a Lyme-like rash with no identified bacterial cause. The 2007 Stafford handbook: "Southern Tick-Associated Rash Illness (STARI) A Lyme-like rash has been noted following the bite of the lone star tick, A. americanum, in south central and southeastern states and given the name Southern tick-associated rash illness (STARI). The rash is indistinguishable from the rash caused by B. burgdorferi. Associated symptoms include fever, headache, fatigue, muscle and joint pain. Little is known about this illness" (CAES 2007). The 2020 IDSA/AAN/ACR Lyme guidelines are candid about the clinical consequence of that uncertainty — "In patients who develop an erythema migrans-like skin lesion following the bite of the lone star tick (Amblyomma americanum), an illness referred to as STARI, we make no recommendation for or against the use of antibiotics *(no recommendation; knowledge gap)" (IDSA 2020). For a full treatment of STARI as a research gap and clinical entity, see STARI and Its Unknown Pathogen.

A crucial negative. A. americanum does not transmit Lyme disease — something the 2007 handbook states explicitly and something public-health communication has repeatedly had to clarify. The 2018 HHS Tick-Borne Disease Working Group public comments put the caveat on record: "the lone star tick is not a competent vector of Borrelia burgdorferi" (HHS 2018).

Alpha-Gal Syndrome (AGS). The best-known — and most distinctive — condition associated with the lone star tick is not an infection at all. The 2018 HHS report to Congress:

"In addition to infections and diseases, tick bites can also cause other life-threatening allergic reactions such as alpha-gal allergy. In the United States, alpha-gal allergy occurs in individuals who have experienced prior bites from the lone star tick (A. americanum). Unlike other tick-borne diseases, this illness is not thought to be caused by an infection, but by the development of the antibody immunoglobulin (Ig) E against the carbohydrate oligosaccharide galactose-alpha1,3-galactose (alpha-gal), which has been found in the gastrointestinal tract of at least one species of tick." — HHS, 2018, pp. 56–57. Tick-Borne Disease Workin...

The 2020 expert review in Expert Review of Clinical Immunology adds the scientific qualification: "Owing to the geographical range and analysis of tick salivary factors, the lone star tick (Amblyomma americanum) appears to be the primary cause of AGS in the U.S.; however, no case-control study has confirmed this link" (T&F 2020). The 2023 CDC MMWR geographic-distribution report gives the epidemiological backup: "Suspected AGS cases were predominantly located in areas where the lone star tick (Amblyomma americanum) is known to be established or reported" (CDC 2023), and "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" (CDC 2023).

The scale of the AGS problem is now substantial. The 2022 HHS disease-prevention subcommittee:

"Accumulating data suggest that the incidence of AGS is on the rise, with the highest number of incidences reported in the southeast region of the United States, which correlates with the expanding geographic distribution of lone star ticks. 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. Disease Prevention and Tr...

This article names the lone-star-AGS association; the clinical syndrome itself is covered in Alpha-Gal Syndrome Explainer, and the biochemistry of how the bite triggers sensitization is covered in How the Lone Star Tick Bite Triggers Alpha-Gal Sensitization.

Other associations. The lone star tick is implicated in additional conditions where vector competence is less clearly established — the 2018 HHS public comments note that "Lone star ticks harbor or vector several other pathogenic or potentially pathogenic bacteria including the spirochete “Borrelia lonestari”, Francisella tularensis, various spotted fever group rickettsiae, and E. ewingii" (HHS 2018). The same authors are also careful about what is unknown: "there are clinical presentations after A. americanum tick bites that have yet to be associated with specific aetiological agents, and there are A. americanum-borne organisms whose pathogenicities are yet unknown" (HHS 2018).

Is the lone star tick spreading into new states?

Yes — and the expansion is well documented across two decades of surveillance. The 2020 CDC surveillance guide for metastriate ticks states the headline directly: "Amblyomma americanum, the lone star tick, has been shown to expand its range northward, with subsequent recognition of lone star tick-associated pathogens" (CDC 2020). The same guide gives the direction of motion: "Amblyomma americanum is generally distributed across the southeastern and south-central United States. The range of this tick is expanding and moving northward and westerly" (CDC 2020).

The CDC reference manual describes the current footprint: "Lone star ticks can be found from central Texas and Oklahoma eastward across the southern states and along the Atlantic Coast as far north as Maine" (CDC 2022). The 2022 HHS ecology subcommittee gives the most precise recent range statement:

"The lone star tick, A. americanum, is expanding northward from its traditionally recognized southeastern United States range into the Mid-Atlantic states, New England, and the provinces of Ontario and Quebec in southern Canada. Westward expansion of A. americanum includes the midwestern states of Michigan, Nebraska, and South Dakota while climate-change-induced range contraction could occur along the Gulf Coast and Lower Mississippi River region. Significantly, the lone star tick is increasing in abundance while populations of the American dog tick, D. variabilis, decline in regions where both species occur. Changes in population balance have significant implications for tick control measures because specific management strategies differ depending upon the tick species to be controlled." — HHS, 2022. Changing Dynamics of Tick...

Alongside the northward push, the tick is also displacing another species in places. Stafford's 2017 review: "Interestingly, the abundance of D. variabilis appears to be decreasing in some areas where A. americanum populations have notably increased, potentially changing the dynamics for risk for certain tick-borne diseases" (OUP 2017). A passive surveillance record from New Jersey documents the shift in what's landing on people. The 2020 CDC Eisen synthesis:

"Jordan and Egizi reported that during 2006–2016, the vector tick species most commonly collected from humans and submitted to a passive tick surveillance system in New Jersey shifted from I. scapularis to A. americanum." — CDC, 2020. Stemming the Rising Tide...

The public-health consequences follow the range. The same 2020 CDC synthesis: "the potential involvement of A. americanum ticks in red meat allergy is concerning because this notorious human-biter is not only abundant in the Southeast but also expanding its range north and thus affecting new human populations" (CDC 2020). The 2018 HHS Working Group public comments anticipated the same trajectory for STARI: "In recent decades, the range of A. americanum has expanded northwards along the eastern seaboard and population abundances are climbing in several north-eastern states. Northern cases of STARI can therefore be expected to increase in Lyme disease endemic areas" (HHS 2018).

The Maine public-health system is watching the northern edge directly. Maine CDC's 2023 annual Lyme report: "This tick does not currently live in Maine, so ehrlichiosis is uncommon. However, as lone star tick populations continue to creep northward, this disease may become more common in Maine in the future" (MaineCDC 2023). On AGS specifically: "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).

Climate is in the background. A 2024 Psychiatric Times review: "The northward expansion of lone star ticks and AGS is amplified by the acceleration of the tick life cycle from climate impacts. One study identified that milder northeastern winters facilitated increased survival of the lone star tick, where patients with AGS may appear in the clinic of unsuspecting clinicians" (PsychT 2024).

Looking forward, the trend appears set. The 2023 CDC MMWR geographic-distribution report:

"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...

That is the shape of the problem the lone star tick now represents: a once-southern species, aggressive and painful to the human host, carrying a pathogen list that includes both long-known bacterial diseases and a protein-based meat allergy that can last a lifetime — and spreading into territory where doctors, patients, and public-health infrastructure are still learning to look for it.

Sources

    Not medical advice. See a healthcare provider for medical decisions. Medical Disclaimer