Think tick season can’t get worse? Think again. A new multi-decade study has found that while blacklegged tick populations in the Northeast haven’t exploded in number, they’re carrying more dangerous diseases than ever before—and that makes every tick bite riskier.
Researchers from Dartmouth College analyzed tick surveillance data from five Northeastern states—Connecticut, Maine, New Hampshire, New York, and Vermont—spanning the period from 1989 to 2022. Their findings, published in Parasites & Vectors, reveal a troubling trend: tick-borne diseases are rising not because of an increase in ticks, but because more ticks are infected.
In New York, for example, the percentage of adult ticks carrying Borrelia burgdorferi (the bacterium that causes Lyme disease) increased from 31% in 2007 to nearly 54% by 2021. In Maine and Vermont, both tick numbers and disease rates have increased, particularly in areas that previously had few ticks.
It’s not just Lyme disease making a comeback. Other illnesses—like anaplasmosis, which can cause high fever and muscle pain, and babesiosis, a parasite-triggered disease with malaria-like symptoms—are also becoming more common as their pathogens spread silently through tick populations.
Worse yet, nymph ticks, which are tiny and harder to spot, continue to be responsible for many infections. Between 2017 and 2021, researchers found that nearly one in five nymphs in certain states carried B. burgdorferi.
Even areas where tick numbers seem controlled aren’t off the hook. Connecticut saw little change in population but a notable rise in pathogen prevalence. Meanwhile, New York recorded the highest tick abundance overall.
It’s no longer just about avoiding ticks—it’s about understanding what they carry. Regular tick checks, protective clothing, and awareness are more critical than ever because today’s ticks may look the same, but they pack a far more dangerous punch.
