50% of Northeastern Adult Ticks Carry Lyme Disease

As the snow melts away in the Northeast, hikers will return to the hills in the spring of 2025, and so will an unwanted tick that carries a severe disease.
Researchers from Dartmouth College recently reported that many states in the Northeast—including Connecticut, New York, New Hampshire, Vermont, and Maine — are at risk for contracting Lyme disease during the spring, summer, and fall.
A new meta-analysis of data collected from 1989 to 2021, led by the Dartmouth study and published in the journal Parasites & Vectors, reveals that 50% of adult blacklegged (Ixodes scapularis) ticks carry the bacteria that causes Lyme disease.
In comparison, up to 25% of younger (nymph) blacklegged ticks also carry the bacteria.
For 2017–2021, the statewide average prevalence of B. burgdorferi ranged from 19% to 25% in I. scapularis nymphs and from 49% to 54% in I. scapularis adults. The statewide average prevalence of all other pathogens in I. scapularis for 2017–2021, including A. phagocytophilum (4–6% for nymphs, 4–9% for adults), B. microti (4–8% for nymphs, 2–13% for adults) and B. miyamotoi (1–2% for nymphs, 1–2% for adults), was considerably less.
“While the bacteria responsible for Lyme disease has a complicated chain of transmission, our results show the relative abundance of blacklegged ticks, and just how many of them are carrying disease-causing pathogens throughout the Northeast,” stated lead author Lucas Price in a press release on January 16, 2025, who was a postdoctoral fellow in geography at Dartmouth at the time of the study.
In 2025, Lyme disease ticks have progressed westward into many midwestern states, which have reported significant increases. However, tick abundance has not changed along the more southern latitudes in the United States.
Various data sources reported about 63,000 Lyme disease cases in 2022, 1.7 times the annual average of 37,000 cases. However, health experts say this data does not account for the actual incidence of Lyme disease.
In the United Kingdom, the Health Security Agency says that approximately 4% of ticks in England and Wales are infected with Lyme disease.
These findings underscore advice from the U.S. CDC that recommends a range of tick bite prevention measures, including conducting full-body tick checks after spending time outdoors.
From a protection perspective, a Lyme disease vaccine candidate is conducting late-stage research with hopeful expectations of positive news in 2026.
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