If you love spending time outdoors in New York, you likely know the drill: tuck your pants into your socks, wear light-colored clothing, and perform a thorough tick check when you get home. It is a necessary routine, because New York consistently ranks at the top of the nation for Lyme disease cases. According to CDC surveillance data tracked on our Tick Bite Tracker map, New York reported a staggering 22,173 confirmed cases in the most recent reporting year, far outpacing every other state in the country.

But why New York? Why does the Empire State, and the broader Northeast, bear such a heavy burden of this tick-borne illness compared to the rest of the country? The answer lies in a complex interplay of ecology, climate change, suburban development, and the unique lifecycle of the blacklegged tick. Understanding these factors is the first step toward protecting yourself and your family every time you head outdoors.

1. The Mighty White-Footed Mouse: The Primary Reservoir

To understand Lyme disease, you have to understand its primary reservoir: the white-footed mouse (Peromyscus leucopus). Lyme disease is caused by the bacterium Borrelia burgdorferi. Ticks are not born with this bacterium; they acquire it when they feed on an infected host.

White-footed mice are incredibly “competent” hosts. This means they are highly efficient at harboring the bacteria without becoming ill themselves, and they easily pass it on to the ticks that feed on them. Other small mammals, such as chipmunks and shrews, also play a role, but the white-footed mouse is the primary driver of Lyme disease transmission in the Northeast. In New York and surrounding states, dense populations of these mice provide an ample, persistent reservoir of the bacteria, ensuring that a high percentage of ticks become infected. A 2025 Dartmouth study found that a striking 50% of adult blacklegged ticks in the Northeast carry the bacteria that causes Lyme disease, with up to 25% of younger nymph-stage ticks also infected.

2. The White-Tailed Deer: Fueling Tick Reproduction

While mice are the primary reservoir for the bacteria, white-tailed deer are crucial for the tick’s reproductive cycle. Deer are considered “incompetent” hosts for Borrelia burgdorferi, meaning they do not transmit the bacteria to ticks. However, adult female ticks rely on deer for their final, critical blood meal before they drop off to lay thousands of eggs.

The historical trajectory of deer populations directly correlates with the rise of Lyme disease. In the 1800s and early 1900s, intense hunting and widespread deforestation nearly wiped out white-tailed deer across the Northeast. As farms were abandoned in the 19th century for the more fertile Midwest, forests slowly reclaimed the land, and deer populations rebounded dramatically. This provided an abundant food source for adult ticks, allowing their populations to skyrocket and spread across the region. Research published in the Proceedings of the National Academy of Sciences has shown that reducing deer density by just 76% can result in a corresponding 76% reduction in tick abundance, illustrating just how tightly the two populations are linked.

3. Suburban Sprawl and the “Edge Effect”

It is not simply that New York has more forests; it is the kind of forests it has. Decades of suburban development and urban sprawl have severely fragmented the landscape of New York and the surrounding region. Large, continuous forests have been broken up into smaller patches interspersed with housing developments, roads, and parks.

This creates what ecologists call “edge habitat,” the transitional zone where a forest meets a lawn or a field. Blacklegged ticks thrive in these shady, moist edge environments, clinging to low vegetation and tall grass at the forest margin, waiting to latch onto a passing host. A landmark study published in the journal Emerging Infectious Diseases found that forest parks in New York City with vegetated buffers and increased landscape connectivity had significantly higher tick densities and higher rates of Borrelia burgdorferi infection in those ticks.

Furthermore, forest fragmentation reduces biodiversity in a way that amplifies disease risk. Larger predators that naturally control mouse populations, including foxes, hawks, and owls, require large tracts of continuous forest to survive and hunt effectively. When forests are fragmented, these predators disappear, allowing white-footed mouse populations to boom unchecked. The result is a perfect storm: surging mouse populations carrying the bacteria, thriving tick populations living in the edge habitats, and millions of people building their homes and spending their leisure time right in the middle of it all.

4. Climate Change: Warmer Winters and Longer Seasons

Climate change is significantly exacerbating the problem by expanding the geographic range of ticks and lengthening their active season. Ticks are highly sensitive to temperature and humidity because they spend the majority of their lives on the forest floor, away from the warmth of a host’s body.

Historically, cold Northeast winters would kill off many ticks or force them into a long period of dormancy. However, milder winters and warmer spring temperatures mean ticks are emerging earlier in the year and remaining active later into the fall. According to researchers at the Cary Institute of Ecosystem Studies, which has monitored ticks in Dutchess County, New York for over 25 years, ticks are now active on any day when temperatures rise above freezing, including in February. This extended active season dramatically increases the window of opportunity for ticks to find a host and for humans to be bitten. The CDC has tracked Lyme disease “hot spots” in the Northeast and upper Midwest and found they increased by more than 320% between 1993 and 2012, a trend that has continued since.

Warmer temperatures also allow ticks to survive in areas further north and at higher elevations that were previously too cold for established populations. New York’s varied geography, from the Hudson Valley to the Adirondacks, means that as the climate warms, suitable tick habitat is expanding into regions that were once relatively safe.

5. A Large, Exposed Population

New York’s sheer population size also plays a role in its case count. With nearly 20 million residents, millions of people live in suburban and semi-rural areas that border tick-infested woodlands. The state is also home to an enormous outdoor recreation culture, with millions of visitors hiking, camping, and exploring its state parks, forests, and trails every year. More people in tick habitat simply means more opportunities for bites and more reported cases. Additionally, New York has a robust public health surveillance system, which means cases are more likely to be reported and counted compared to states with less comprehensive tracking.

What You Can Do to Stay Safe

The combination of abundant reservoir hosts, thriving reproductive hosts, fragmented landscapes that favor tick survival, and a warming climate has made New York the epicenter of Lyme disease in the United States. While we cannot easily change the ecology of the Northeast, we can change our behavior. When enjoying the beautiful trails and parks of New York, always keep these precautions in mind:

• Dress defensively: Wear light-colored clothing, long pants tucked into your socks, and long sleeves to make ticks easier to spot and harder to reach skin.
• Use repellent: Apply EPA-registered insect repellents containing DEET, picaridin, or IR3535 to exposed skin and clothing.
• Stay on the trail: Avoid walking through tall grass, brush, and leaf litter where ticks wait for a passing host.
• Check thoroughly: Perform a full-body tick check on yourself, your children, and your pets immediately after spending time outdoors. Pay special attention to the scalp, behind the ears, armpits, groin, and behind the knees.
• Shower promptly: Showering within two hours of coming indoors can help wash off unattached ticks before they have a chance to bite.
• Know the symptoms: If you develop a bull’s-eye rash, fever, fatigue, or joint pain within days to weeks of a tick bite, contact your healthcare provider immediately. Early treatment with antibiotics is highly effective.

By understanding the ecological and environmental factors driving Lyme disease in New York, we can better appreciate the importance of these preventative measures and make informed decisions every time we head outdoors. Stay trail ready, stay tick aware, and stay safe.

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Sources

[1]  CDC NNDSS 2023 Surveillance Data, as displayed on the TrailReadySolutions.com Tick Bite Tracker.

[2]  Rogovskyy, A.S. et al. (2024). “Do white-footed mice, the main reservoir of the Lyme disease spirochete, develop immunity?” Infection and Immunity. American Society for Microbiology.

[3]  Price, L. et al. (2025). “Northeast: 50% of Adult Ticks Carry Lyme Disease.” Parasites & Vectors. Dartmouth College.

[4]  Levi, T. et al. (2012). “Deer, predators, and the emergence of Lyme disease.” Proceedings of the National Academy of Sciences.

[5]  VanAcker, M.C. et al. (2019). “Enhancement of Risk for Lyme Disease by Landscape Connectivity, New York, New York, USA.” Emerging Infectious Diseases, CDC.

[6]  Ostfeld, R. (Cary Institute of Ecosystem Studies). “Climate change and tick-borne disease risk.” caryinstitute.org.

[7]  Ginsberg, H.S. et al. (2021). “Why Lyme disease is common in the northern US, but rare in the south.” PLOS Biology.

[8]  New York State Department of Health. “Lyme Disease and Other Diseases Carried by Ticks.” health.ny.gov.

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