Lyme disease is the most commonly reported vector-borne illness in the United States, and its prevalence in New York State (NYS) makes understanding the risk a high priority for residents and visitors. The question of what percentage of ticks carry the bacteria responsible, Borrelia burgdorferi, is highly relevant to public health awareness and prevention efforts. Surveillance data confirms that a significant portion of the tick population in NYS is infected. Knowing the specific rates and the factors that influence them provides a clearer picture of the hazard when enjoying the outdoors.
The Primary Vector and Infection Rates
The only tick species proven to transmit the bacteria causing Lyme disease in New York State is the blacklegged tick, commonly known as the deer tick, or Ixodes scapularis. This tiny arachnid acquires the bacteria from small mammals like mice and then passes it to humans during a subsequent blood meal. The overall percentage of infected blacklegged ticks varies widely by region and life stage, but statewide data provides a clear indication of the minimum risk.
Surveillance conducted by the New York State Department of Health indicates that, on average, approximately 51% of adult blacklegged ticks and about 27% of tick nymphs statewide carry the Lyme bacteria. The difference in these percentages is partially due to the longer feeding time that adult ticks have over their lifespan, providing more opportunities to become infected. Adult ticks are active mainly during the cooler months of spring and fall, and are roughly the size of a sesame seed.
The risk to humans is often disproportionately linked to the smaller, less visible nymph life stage. Nymphs are young ticks active primarily from mid-May through August and are about the size of a poppy seed. Despite their lower infection rate, nymphs are the most common source of human infection because their minuscule size allows them to feed undetected. Nymphal infection rates in some NY areas range from 15% to over 23%, underscoring the consistent presence of the pathogen.
Geographic Variance Across New York State
The risk of encountering an infected tick is not uniform across the state, as the geographic distribution of Lyme disease is highly unequal and continually expanding. Historically, the disease focused on the southeastern portion of New York State, particularly the lower Hudson Valley region, including Westchester County. This area continues to report high case numbers, and the core of the infection cluster has been observed migrating northward along the Hudson River corridor into counties like Putnam, Dutchess, and Columbia.
The highest incidence rates of human cases are frequently found in the Capital District region, while the Metropolitan region reports the largest total number of cases due to its dense population. The prevalence of infected ticks in the Hudson Valley reflects this, with surveillance data showing infection rates of over 21% for nymphs and 50% for adults. Areas like Western New York and portions of the Adirondacks have historically experienced lower incidence rates.
Variation in infection rates is influenced by local ecological factors, including climate and habitat that favor the tick life cycle. The density of host animals directly impacts the level of risk. White-footed mice are the primary reservoir for the bacteria, while white-tailed deer are the main reproductive hosts for adult ticks. Therefore, areas with high deer and mouse populations, along with abundant forest fragmentation, tend to have the highest concentration of infected ticks.
Minimizing Personal Risk
Given the high percentage of infected ticks, especially in the state’s eastern half, practical preventative measures are necessary to reduce exposure. One effective strategy involves using Environmental Protection Agency (EPA)-registered insect repellents on exposed skin, such as those containing DEET (at concentrations up to 30-35%), picaridin, or IR3535. For added protection, clothing and gear can be treated separately with permethrin, a product that kills ticks on contact, but this chemical must never be applied directly to the skin.
When spending time outdoors, wearing light-colored clothing makes it easier to spot ticks before they attach. Tucking pants into socks and shirts into pants creates a physical barrier, preventing ticks from reaching the skin. Clearing leaf litter, keeping lawns mowed, and creating a barrier of wood chips or gravel can also make the home environment less hospitable to ticks.
The most important step in prevention is the prompt and proper removal of any attached tick. It is recommended to shower or bathe within two hours of coming indoors to wash off unattached ticks and perform a full-body check. If a tick is found attached, use fine-tipped tweezers to grasp it as close to the skin’s surface as possible and pull upward with steady, even pressure. While transmission risk is generally low if the tick is removed within the first 36 to 48 hours, prompt removal is always advised because the bacteria can sometimes be transmitted in less than 24 hours.