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A recent study conducted by researchers from Dartmouth and various health and agricultural agencies has revealed concerning findings regarding the spread of Lyme disease in the Northeastern United States. Published in Parasites and Vectors, the study indicates that half of the adult blacklegged ticks—commonly known as deer ticks—are carrying the bacteria responsible for Lyme disease. Additionally, up to 25% of younger nymph ticks also carry the bacteria.
The study, which analyzed data spanning from 1989 to 2021, focused on states including Connecticut, New York, New Hampshire, Vermont, and Maine. Researchers conducted a meta-analysis to evaluate the abundance of blacklegged ticks and the presence of pathogens, including Borrelia burgdorferi, the bacterium that causes Lyme disease. The data collected highlighted alarming trends in tick-borne diseases across the region.
Lyme disease, first identified in Lyme, Connecticut in 1975, is transmitted by infected ticks and can cause symptoms such as rashes, fever, chills, muscle aches, and, in severe cases, neurological problems. If untreated, the disease can lead to more serious complications, including joint pain and heart problems. Infected ticks acquire the bacteria by feeding on small animals, such as white-footed mice and chipmunks, which are “competent hosts” for the bacteria.
Blacklegged ticks are not born with the bacteria but can acquire it after feeding on an infected animal. Once infected, ticks can transmit the bacteria to humans during subsequent feedings. While white-tailed deer serve as a food source for ticks, they are “incompetent hosts” and do not transmit the Lyme bacteria.
The study found that blacklegged ticks undergo three feeding stages in their two-year life cycle: as larvae in summer, as nymphs the following spring, and as adults in the fall. While adult ticks are larger and easier to spot, nymphs are about the size of a poppy seed and pose a greater risk due to their difficulty in being detected. Ticks need to be attached to a person for at least 24 hours to transmit Lyme disease bacteria.
The research also suggests a significant increase in the percentage of ticks carrying Lyme disease over the past few decades. Despite the general stability in the overall number of ticks, the prevalence of ticks carrying Lyme disease bacteria has risen.
The findings underscore recommendations from the Centers for Disease Control and Prevention (CDC) and health professionals for individuals in affected areas to take preventive measures against tick bites. These measures include conducting thorough tick checks after spending time outdoors, particularly in areas where ticks are known to carry pathogens.
The Dartmouth team has created one of the most comprehensive tick abundance and pathogen prevalence datasets in the United States, establishing a baseline for future studies. The researchers are also investigating the potential links between climate change and the increasing prevalence of blacklegged ticks and Lyme disease in the region.
As the spread of Lyme disease continues to be a pressing public health concern, the study serves as a reminder of the importance of vigilant prevention efforts and continued research into the ecological and environmental factors that contribute to the rise in tick-borne diseases.
For further information, the full study is available in Parasites and Vectors (2024).
