Reported cases of Lyme disease, babesiosis, and anaplasmosis have climbed steadily across the United States for nearly two decades, and the latest federal surveillance data show no plateau. More than 89,000 Lyme disease cases were reported to the CDC in 2023, while anaplasmosis case files now extend through that same year with continued growth. Blacklegged ticks, the primary vector for all three pathogens, have established populations in counties far beyond their historical range, and the diseases they carry are hitting northern states especially hard.
Three tick-borne diseases accelerating at once across the Northeast
The scale of the increase is striking when measured over time. A CDC Vital Signs analysis found that tick-borne disease reports more than doubled between 2004 and 2016, with Lyme disease accounting for the largest share of that burden. Babesiosis and anaplasmosis, though less common in absolute numbers, posted sharp percentage gains during the same window, particularly in states where blacklegged ticks were newly established.
That trajectory has not reversed. CDC anaplasmosis data files document reported cases from 2000 through 2023, and the trend line points upward across nearly every reporting year. Babesiosis tells a similar story: a CDC surveillance analysis covering 2011 through 2019 found that incidence increased significantly in Vermont, Maine, and New Hampshire, three states where the disease was relatively rare a generation ago. The CDC’s babesiosis portal lists case data extending through 2023, reinforcing the pattern of expansion rather than stabilization.
One hypothesis worth testing against these data is whether counties that gained the most forest cover between 2000 and 2020 experienced the steepest per-capita increases in all three diseases, even after accounting for rising temperatures. Reforestation creates habitat for white-tailed deer and white-footed mice, the key hosts that sustain blacklegged tick populations. If forest regrowth is a stronger predictor than warming alone, prevention strategies would need to account for land-use change, not just climate. No published study has yet paired county-level forest-cover change with disease incidence and temperature data at the same spatial resolution, leaving this question open.
CDC surveillance records and tick-range mapping tell a consistent story
The evidence base for these trends rests on several interlocking federal datasets. The National Notifiable Diseases Surveillance System, accessible through the CDC’s NNDSS portal, provides finalized annual U.S. counts for 2016 through 2023, offering the most reliable year-by-year comparison once provisional weekly totals are reconciled. NNDSS distinguishes clearly between provisional weekly counts and finalized annual totals, a distinction that matters because early-season numbers can shift substantially before states complete their case reviews.
The geographic story is equally clear. A foundational study in the Journal of Medical Entomology compiled distribution records for blacklegged ticks from 1907 through 1995, drawing on expert questionnaires, MEDLINE searches, and the National Tick Collection. That historical baseline has since been updated by peer-reviewed mapping work showing that blacklegged tick populations have spread into counties well beyond the mid-1990s footprint, driven by reforestation, host animal availability, and warming winters. The overlap between these expanding tick ranges and rising case counts for Lyme disease, babesiosis, and anaplasmosis strengthens the argument that vector expansion is a central driver of risk.
Lyme disease dominates the national tick-borne disease burden by volume. The CDC reports that over 89,000 Lyme cases reached federal surveillance in 2023, though the agency has long noted that actual infections likely exceed reported totals by a wide margin because many cases go undiagnosed or unreported. Babesiosis, caused by a parasite rather than a bacterium, can be life-threatening for older adults and immunocompromised patients, making its geographic spread a direct clinical concern. Anaplasmosis, a bacterial infection that can cause fever, headache, and dangerously low white blood cell counts, rounds out the trio of diseases riding the same vector into new territory.
Gaps in data and prevention that residents should watch
Several important questions remain unanswered. Finalized 2024 case counts from NNDSS are not yet available, so the most recent complete picture of all three diseases covers 2023. Provisional weekly tables offer partial glimpses of more recent activity, but those numbers can change as states finalize their reports. Anyone tracking local risk should be aware that provisional data and finalized annual totals can diverge, a limitation the CDC documents on its NNDSS data pages.
No primary CDC dataset directly pairs county-level changes in deer or rodent host density with tick distribution records. That gap makes it difficult to isolate how much of the disease surge stems from ecological factors like reforestation versus climate-driven range expansion. Peer-reviewed studies discuss both drivers, but the data needed to weigh them against each other at fine geographic scales do not yet exist in a single, publicly accessible format. State health departments, meanwhile, do not consistently release case reports with symptom onset dates, which would help clarify whether increases reflect earlier seasonal activity, better testing, or true growth in infections.
These blind spots have practical consequences. Without detailed host and land-use data, local officials may underestimate future hot spots where forest regrowth and expanding deer herds could support explosive tick population growth. Inconsistent reporting of onset dates and travel histories can also blur the line between locally acquired infections and cases contracted elsewhere, complicating efforts to map where residents face the highest day-to-day risk.
For people living in or traveling to the Northeast and Upper Midwest, the implications are straightforward even if some scientific questions remain unresolved. The same blacklegged ticks can transmit Lyme disease, babesiosis, and anaplasmosis, sometimes in a single bite, and the surveillance record shows all three infections becoming more common. Personal protection measures-using EPA-registered repellents, performing daily tick checks after time outdoors, treating clothing with permethrin, and showering soon after coming inside-remain the first line of defense. Pet owners should talk with veterinarians about tick prevention for dogs, which can bring ticks into homes even if people spend little time in wooded areas.
Clinicians in expanding risk zones face their own challenges. Because early symptoms of these infections overlap-fever, fatigue, muscle aches-providers must decide quickly whether to test for one pathogen, several, or treat empirically while results are pending. Awareness that babesiosis and anaplasmosis are rising alongside Lyme disease can prompt broader testing panels, especially for older or immunocompromised patients who may deteriorate rapidly without targeted therapy.
Looking ahead, the combination of rising case counts, expanding tick ranges, and persistent data gaps suggests that tick-borne diseases will remain a growing public health issue rather than a short-term spike. Filling those gaps-by integrating land-use change, host populations, and high-resolution surveillance-could sharpen forecasts and guide prevention campaigns. Until then, residents in affected regions will have to navigate a landscape where the risks are clearly increasing, even if the precise mix of ecological and climatic drivers has yet to be fully untangled.
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*This article was researched with the help of AI, with human editors creating the final content.
