Tick Risk by Geography How to Read the Map You Actually Live On

Most tick-borne disease is regional. The tick on your ankle in Connecticut is not the tick on your ankle in Arkansas, and the pathogens each one carries are different. This article is about how to orient yourself on the map you actually live on, and where to look when the national picture is too coarse to answer your question.

Why geography is the first question to ask

The CDC's 2016 clinical guidance on tickborne rickettsial diseases states the underlying principle plainly:

"The epidemiology of each tickborne rickettsial disease reflects the geographic distribution and seasonal activities of the tick vectors and vertebrate hosts involved in the transmission of these pathogens, as well as the human behaviors that place persons at risk for tick exposure, tick attachment, and subsequent infection (Box 1)." — CDC, 2016, pp. 5–6. Diagnosis and Management...

In practical terms: which diseases are plausible for you depends on where you are, where you've been, and what ticks live in those places. But geography alone does not determine risk — what you do in those places compounds the baseline regional exposure. CDC's 2016 guidance also notes that a careful clinical history should include questions about "recreational or occupational exposure to tick-infested habitats" (CDC 2016) and "travel to areas where tickborne rickettsial diseases are endemic" (CDC 2016) — the geography question runs through diagnosis as much as prevention.

The HHS 2018 Tick-Borne Disease Working Group's report to Congress put the surveillance-gap version of this concern in direct language:

"Lack of surveillance data in certain regions, or even localities within regions, gives a potentially false perception of tick-borne disease risk and hinders patients’ access to prevention education and timely, accurate diagnosis and care." — HHS, 2018, pp. 19–20. Tick-Borne Disease Workin...

Knowing where the risk lives — and doesn't — is a baseline for everything downstream.

The U.S. map, by region

The clearest starting point is the CDC's 2022 Tickborne Diseases Reference Manual (6th Ed.), which lists where each major human-biting tick is found and what it transmits.

The Northeast, Upper Midwest, and Mid-Atlantic. The blacklegged tick (Ixodes scapularis), also called the deer tick, is "Widely distributed across the eastern United States" (CDC 2022), and "The greatest risk of being bitten exists in the spring, summer, and fall in the Northeast, Upper Midwest, and mid-Atlantic" (CDC 2022). When exactly those risk peaks occur is a separate dimension of the seasonal calendar. Lyme disease follows the same map: the CDC manual states that "Lyme disease is most frequently reported from the upper midwestern, northeastern, and mid-Atlantic states where it is spread by Ixodes scapularis ticks" (CDC 2022), and lists high-incidence states explicitly:

"High-incidence states include Connecticut, Delaware, Maine, Maryland, Massachusetts, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, Virginia, Washington D.C., West Virginia, and Wisconsin. While these states account for the majority of cases, the geographic area of risk is expanding to include neighboring states." — CDC, 2022, pp. 8–9. Tickborne Diseases of the...

Anaplasmosis and babesiosis cluster in the same area for the same reason. The CDC manual reports that anaplasmosis is "most frequently reported from the Upper Midwest and northeastern United States in areas that correspond with the known geographic distribution of Lyme disease and other Ixodes scapularis-transmitted diseases" (CDC 2022), and babesiosis is "most frequently reported from the Northeastern and Upper Midwestern United States in areas where B. microti is endemic" (CDC 2022). Powassan virus disease shares the footprint: "Most cases have occurred primarily in northeastern states and the Great Lakes region" (CDC 2022).

The Southeast and South-Central U.S. The lone star tick (Amblyomma americanum) dominates here. The CDC manual describes it as "Widely distributed in the eastern United States, but more common in the South" (CDC 2022), with a range that "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). Ehrlichiosis tracks that range: the same CDC manual reports that "Ehrlichiosis is most frequently reported from the southeastern and south-central United States, from the East Coast extending westward to Texas" (CDC 2022). A 2019 American Society for Microbiology review adds that "E. chaffeensis and E. ewingii are found in the southeastern, southern, central, and mid-Atlantic portions of the United States" (ASM 2019).

A 2020 CDC paper in Emerging Infectious Diseases sketches the regional contrast in one sentence:

"In contrast to the situation in the Northeast and upper Midwest, I. scapularis ticks are only a minor public health threat compared with Amblyomma ticks in the Southeast." — CDC, 2020. Stemming the Rising Tide...

The Rocky Mountains and the West. The Rocky Mountain wood tick (Dermacentor andersoni) is found in the "Rocky Mountain states" (CDC 2022). The western black-legged tick (Ixodes pacificus) lives "In the Pacific Coast states" (CDC 2022). Colorado tick fever is geographically narrow — the CDC manual notes that the "geographic range of Colorado tick fever virus includes the Western United States, primarily Colorado, Utah, Montana, and Wyoming" (CDC 2022). Tick-borne relapsing fever is rarer still and exposure-specific: in the U.S., the CDC manual reports that it "usually occurs in mountainous areas of Western states, where it is associated with exposure to soft ticks in rustic cabins (B. hermsii), and in Texas, where it is most often associated with exposure to soft ticks in caves (B. turicatae)" (CDC 2022).

The Southwest and U.S.–Mexico border. The brown dog tick (Rhipicephalus sanguineus) has become the RMSF story in this region. CDC's 2022 manual notes that "RMSF is most often transmitted by the American dog tick in the Eastern, Central, and Western United States; by the Rocky Mountain wood tick in the Rocky Mountain states; and by the brown dog tick in the Southwestern United States, along the U.S.-Mexico border" (CDC 2022). CDC's 2016 guidance traces the arc of emergence: "The brown dog tick, Rh. sanguineus, has been a recognized vector of R. rickettsii in Mexico since the 1940s; however, Rhipicephalus-transmitted R. rickettsii in the United States was not identified until 2003, when it was confirmed in a child on tribal lands in Arizona" (CDC 2016). The burden in the affected tribal communities is severe:

"A notable regional increase in the reported incidence of SFG rickettsiosis occurred in Arizona during 2003–2013. Over this period, approximately 300 cases of RMSF and 20 deaths were reported from American Indian reservations in Arizona compared with three RMSF cases reported in the state during the previous decade. Since identification of the first case of locally transmitted RMSF in 2003, RMSF has been found to be endemic in several American Indian communities in Arizona." — CDC, 2016, pp. 5–6. Diagnosis and Management...

The Gulf Coast and mid-Atlantic focal populations. The Gulf Coast tick (Amblyomma maculatum) is, per the CDC manual, "Distributed primarily in the southeastern United States, with focal populations in the northeastern, midwestern, and southwestern United States" (CDC 2022). A 2024 HHS scoping review documents one recent focal-population detection:

"A survey found the Gulf Coast tick (A. maculatum) in Staten Island and Brooklyn, New York, as well as in Atlantic and Cumberland Counties, New Jersey, indicating increased spread of this species along the northern Atlantic coast. Five out of 10 collected adult Gulf Coast ticks tested positive for R. parkeri, the pathogen responsible for R. parkeri rickettsiosis." — HHS, 2024, pp. 13–14. Tick-Borne Diseases and A...

The ranges are moving

Current maps are snapshots of a moving picture. The 2018 HHS Tick-Borne Disease Working Group report to Congress puts the Lyme expansion in blunt terms:

"The number of U.S. counties now considered to be of high incidence for Lyme disease has increased by more than 300% in the Northeastern states and by approximately 250% in the North-Central states." — HHS, 2018, pp. 3–4. Tick-Borne Disease Workin...

The same 2018 report describes the trajectory of the Lyme map: "The geographic range of Lyme disease cases has expanded since its first appearance in Lyme, Connecticut, in 1975 and has consistently spread northward, southward, and westward. The high-risk regions of the Northeast and Upper Midwest appear to be converging over time in the Ohio River Valley to form one contiguous range" (HHS 2018). A 2022 HHS Tick Ecology subcommittee report adds that "From 1996 to 2016, the number of U.S. counties fulfilling the criteria for having an established population of I. scapularis increased by 45%" (HHS 2022), and that "Geographic range of the Gulf Coast tick, A. maculatum, is expanding in multiple directions" (HHS 2022).

New species are showing up where they weren't. The same 2022 HHS report notes that "established populations of the exotic Asian longhorned tick detected in New Jersey in 2017, followed by the subsequent detection of this tick species across the eastern United States (detected in 17 states at the time of this writing)" (HHS 2022). A 2024 HHS scoping-review update quantifies one dimension of babesiosis's northward creep: "From 2011 to 2019, reported babesiosis cases (mostly caused by Babesia microti in the United States) increased significantly in Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Rhode Island, and Vermont" (HHS 2024), with "Maine, New Hampshire, and Vermont now have endemic transmission" (HHS 2024). A 2025 review in ScienceDirect links part of the pattern to climate:

"For instance, the United States, Mexico, and Canada have experienced significantly warmer winter temperatures due to climate change in recent decades. This observed increase in temperature is likely to have caused the expansion and shifting of the potential distribution of several tick species to higher latitudes and altitudes. Consequently, changes in tick development and phenology are expected to contribute to an escalation in Lyme disease incidence within the northeastern region as well as its northward spread into Canada." — Elsevier, 2025. A Comprehensive Review of...

Low incidence is not no risk

"Low incidence" is not the same as "no risk." CDC's 2016 guidance notes that "SFG rickettsiosis cases have been reported from each of the contiguous 48 states and the District of Columbia" (CDC 2016). The 2022 CDC manual reports that tularemia "has been reported in all states except Hawaii, but it is most common in the south-central United States, the Great Plains region, and parts of Massachusetts" (CDC 2022). The 2018 TBDWG report notes that "I. scapularis and I. pacificus ticks have been found in approximately 50% of counties in the U.S., including many counties on the West Coast" (HHS 2018), and that Lyme disease on the West Coast remains "an important concern" (HHS 2018).

The 2018 TBDWG report also identifies a downstream consequence of the low-incidence-equals-no-risk assumption:

"Complicating the issue, health care providers in low incidence regions, such as the South and the West Coast, are often under the impression that Lyme disease does not occur in their state and therefore do not conduct the two-tiered test on patients with symptoms consistent with Lyme disease. As a result, those patients and their family members may need to travel long distances, often paying out-of-pocket, to seek diagnosis and treatment from practitioners in high incidence states (see chapter 7 on Access to Care and Patient Outcomes)." — HHS, 2018, pp. 23–24. Tick-Borne Disease Workin...

Travel matters for the same reason. CDC's 2016 guidance notes that "Travel history within and outside of the United States can provide an important clue in considering the diagnosis of a tickborne rickettsial disease. Travel from an area where tickborne rickettsial diseases are endemic within 2 weeks of the onset of a clinically compatible illness could support a presumptive diagnosis of tickborne illness" (CDC 2016). If you were bitten in Arkansas and developed symptoms in Oregon, your clinician needs to know about Arkansas.

Outside the U.S.

Tick-borne disease is not a U.S. story. A 2023 MDPI Pathogens worldwide review sketches the global frame:

"However, the information available on ticks and TBD varies between countries and regions as disclosed using a raw bibliometric analysis. Most of the studies (44.1%) came from Europe and the USA while Asia, North America, and Africa contributed to 36.2% of the publications. The rest of the countries/regions each contributed less than 5.5% of the publications. Reasons behind these differences may be the economic problems regarding publication in pay-to-publish journals or an obvious lack of awareness of ticks on either livestock or humans. As a rule, resource-poor countries produced fewer papers on the topic, and the contributions in this review reflect this lack of awareness." — MDPI, 2023. Perception of Ticks and T...

Europe. The 2022 CDC manual notes that, "Outside North America, Borrelia spp. that cause Lyme disease are transmitted through the bite of infected Ixodes ricinus and I. persulcatus ticks" (CDC 2022), and that for Lyme in Europe, "Incidence is highest in Central and Eastern European countries" (CDC 2022). For tick-borne encephalitis (TBE), the CDC manual reports the virus is "Endemic in focal areas of Europe and Asia, extending from western and northern Europe through to northern and eastern Asia. The highest disease incidence has been reported from the Baltic states, Slovenia, and Czech Republic" (CDC 2022).

Mexico and the Americas. A 2023 MDPI worldwide review reports that in Mexico, "Rickettsiosis by R. rickettsii is the most important TBD in humans in northwestern Mexico, with mortality rates of 30–40%" (MDPI 2023). In Brazil, per the same review, "Rickettsia rickettsii infection is the major human tick-borne disease in Brazil, the “febre maculosa Brasileira” (Brazilian spotted fever)" (MDPI 2023).

Asia and Australia. A 2025 review in ScienceDirect reports that for Lyme disease in China, "seropositivity ranged from 1.8% to 14.5% from 2005 to 2020, with the highest seropositivity rate in northeast and northwest China" (Elsevier 2025). The 2023 MDPI review reports that in Turkey, "Crimean-Congo hemorrhagic fever cases were mostly documented in rural areas in the central and northern regions of the country where agricultural and animal husbandry activities are common" (MDPI 2023). In Australia, the same MDPI review records the unresolved position: "Despite the lack of scientific evidence for the presence of the causative agent, Borrelia burgdorferi s.l, and vector ticks of the I. ricinus group, thousands of Australians have reported suffering from non-specific arthritic, cardiological, neurological, and dermatological symptoms following a tick bite" (MDPI 2023).

How to find local-to-you data

The national picture is the starting point, not the endpoint. CDC's own post-tick-bite clinical guidance makes the handoff explicit:

"Post-exposure prophylaxis for Lyme disease Antimicrobial prophylaxis for the prevention of Lyme disease following tick bite may be beneficial in certain circumstances. A single dose of doxycycline can lower the risk of Lyme disease when: • The tick bite occurred in a state where Lyme disease incidence is high or in an area where >20% of ticks are infected with Borrelia burgdorferi. Contact your local health department for information about tick infection rates in your area. • The attached tick can be identified as an adult or nymphal blacklegged tick. • The estimated time of attachment is ≥36 hours based on the degree of tick engorgement with blood or likely time of exposure to the tick. • Prophylaxis can be started within 72 hours of tick removal. • The patient has no contraindication to doxycycline." — CDC, 2021, pp. 1–2. Guidance for Clinicians:...

One sentence inside that block names the step: contact your local health department for information about tick infection rates in your area. That local contact will tell you what percentage of ticks in your region actually carry disease — a number that shapes whether post-exposure prophylaxis is warranted. That is a concrete thing national maps can't do for you.

CDC tick surveillance maps. The 2020 CDC Surveillance for Ixodes scapularis and Documentation of Pathogens guide states the intent directly:

"CDC aims to collate tick surveillance data to make county-level data available to the public on national-scale maps that will be displayed on the CDC website, and regularly updated." — CDC, 2020, pp. 10–11. Guide to the Surveillance...

The same guide defines what "established" versus "reported" actually mean on those county-level maps:

"• Established: > 6 ticks of a single life stage or > 1 life stage collected per county within a 12-month period • Reported: < 6 ticks of a single life stage collected per county within a 12-month period • No records (note: should not be interpreted as absence of occurrence): o For this objective and all others, ticks should be identified to species and life stage using published taxonomic keys o For counties reporting new records, voucher specimens supporting the status change should be archived in curated collections" — CDC, 2020, pp. 10–11. Guide to the Surveillance...

A related feature of these classifications is asymmetry: a county without records is not confirmed tick-free — it may be unsampled. The guide itself cautions against reading "no records" as absence.

State and local health departments. State health departments carry the granular data that CDC aggregates. The 2022 CDC manual illustrates the expected handoff — for Heartland virus disease, a clinician should "Please contact your state health department if you have a patient with an acute illness that may be compatible with Heartland virus disease" (CDC 2022). That handoff is not only for clinicians. State epidemiology programs typically publish tick-borne disease case counts, species surveillance reports, and regional risk alerts — with wide variation in detail.

The gaps are worth naming. A 2019 NACCHO survey of local environmental-health programs captured the variability directly: "One respondent reported concern that their state program only conducts two tick drags per county. In counties with large land area and population, the two tick drags do not accurately capture the different habitats in the county" (NACCHO 2019). The resolution of public surveillance varies enormously from state to state — and sometimes within a state.

Tick-ID and community science. A 2025 NACCHO guide for health departments points to one community-contributed data source:

"TickApp is a community-based science smartphone app developed jointly by Vector-Borne Disease Center of Excellence researchers in the Midwest and Northeast that can help inform people about tick safety and help contribute to human-tick encounter surveillance data. Data collected from TickApp allows researchers to create a map of where the encounters occurred and beta-test simple tick identification methods for further educational use." — NACCHO, 2025. Rise in Tick Bites Observ...

European data sources. ECDC's communication guidance for member-state agencies makes a parallel point on the European side: "the importance of receiving more locally adapted information as regards which disease(s) is prevalent in the area where people live and which are the risk areas (e.g. a map showing in which parts of a country/region a disease is most prevalent, statistics on the development of the disease(s), or graphs)" (ECDC). National tick surveillance programs vary across member states.

Where "your backyard" fits on the map

For many readers in the eastern U.S., the relevant geography is smaller than a state. A 2020 CDC paper in Emerging Infectious Diseases characterizes the scale:

"Today, the threat posed by human-biting ticks is more widespread across the eastern United States, increasingly complex (multiple tick species and >10 notable tickborne pathogens), and, across tick species, more spatially diffuse (including backyards, neighborhood green spaces, and public recreation areas)." — CDC, 2020. Stemming the Rising Tide...

The 2016 CDC guidance makes the point more concretely: "In areas endemic for ticks, activities as commonplace as playing in a backyard, visiting a neighborhood park, gardening, or walking dogs are potential sources of tick exposure" (CDC 2016). In Connecticut and the Northeast, the 2022 HHS Tick Ecology report notes that "up to three quarters of tick bites in Connecticut and the Northeast are estimated to be acquired in residential settings where forested tick and host habitat is present" (HHS 2022). If you have a dog in one of these regions, tick-borne disease in your dog can serve as a local risk indicator for your family — a different kind of geographic signal.

Local risk — at the county, yard, or park level — is the resolution at which decisions about repellent, clothing, tick checks, and landscaping actually happen. CDC and state health department maps are the starting points. For most readers, the missing piece is knowing which questions to ask of their own local public-health authorities — and that begins with knowing the name of the region they live in, and what lives there with them.

Sources

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