In most of the Northeast, being bitten by a blacklegged tick, also called a deer tick, is a risk during the spring, summer, and fall. A new Dartmouth study, published in Parasites and vectorsfinds that 50% of adult blacklegged ticks carry the bacteria that causes Lyme disease, while 20% to 25% of younger (nymphal) blacklegged ticks carry the bacteria .
A team of researchers from universities, health departments and agricultural agencies across the Northeast conducted a meta-analysis of data on how many blacklegged ticks there are and how many of them have the potential to transmit pathogens responsible for Lyme disease and three other ticks. virus-borne diseases in the Northeast from 1989 to 2021, including Connecticut, New York, New Hampshire, Vermont, and Maine.
Data was collected in Maine beginning in 1989, while most other states began collecting data in the mid-2000s. Massachusetts and Rhode Island were not represented in the study due to data not being available or They were insufficient.
Lyme disease was first discovered in Lyme, Conn., in 1975. Its symptoms can vary depending on the stage and severity of the disease, but can include rash, fever, chills, fatigue, muscle or joint pain, and swelling of the joints. lymph nodes. If left untreated, prolonged and more serious symptoms may develop.
Lyme disease is caused by a bacteria called Borrelia burgdorferi. Some, but not all, white-footed mice, chipmunks, birds, squirrels, and other small animals carry the bacteria in their blood, making them “competent” hosts. Blacklegged ticks are not born infected with the Lyme disease bacteria. But when a blacklegged tick feeds on an infected host, it can contract the bacteria that causes Lyme disease and then potentially transmit it to humans through its bite. Other animals, such as white-tailed deer, are “incompetent hosts,” so while they are a food source for blacklegged ticks, they do not transmit Lyme disease bacteria.
Blacklegged ticks typically consume three blood meals over the course of a two-year life cycle: after they hatch into larvae in mid-summer of their first year; as nymphs during late following spring, often in May or June; and in adulthood that drop, most likely between September and November.
In general, ticks must remain attached to a person for at least 24 hours to transmit the Lyme disease bacteria. So, although adult blacklegged ticks are more likely to carry the bacteria than younger ticks, because they are larger, about the size of a sesame seed, there is particular concern for younger ticks or nymphs, which They are only the size of a poppy. seeds, making them difficult to detect.
“While the bacteria responsible for Lyme disease has a complicated chain of transmission, our results show the relative abundance of blacklegged ticks and how many of them carry disease-causing pathogens across the Northeast,” says lead author Lucas Price. , who was a postdoctoral fellow in geography at Dartmouth at the time of the study and is now a wildlife biologist at the Department of the Interior’s Bureau of Land Management.
The researchers analyzed the abundance of blacklegged ticks and the presence of Lyme disease bacteria and other pathogens in order to determine how blacklegged ticks and the pathogens they carry are changing over time and space.
“Unlike the well-documented spread of blacklegged ticks and Lyme disease over the past 30 years, we found very small changes in the abundance of blacklegged ticks, but we think this is probably because they normally do not We start sampling a location for blacklegged ticks until they are established,” says senior author Jonathan Winter, associate professor of geography and director of the Applied Hydroclimatology Group at Dartmouth. “However, we found an increase in the percentage of blacklegged ticks carrying the Lyme disease bacteria.”
These findings underscore advice from the Centers for Disease Control and Prevention and health professionals, who recommend a variety of tick bite prevention measures, including performing whole-body tick checks after spend time outdoors in regions where there are pathogen-carrying ticks. While much of the data was already publicly available before the study, the team made the surveys consistent across states, creating one of the most comprehensive pathogen prevalence and tick abundance data sets in the United States and establishing a baseline that can be used in the future.
Researchers have another study underway examining the relationship between climate change and the prevalence of blacklegged ticks and Lyme disease in the Northeast.
Joseph Savage, a graduate student in Dartmouth’s Ecology, Evolution, Environment and Society program, also contributed to the study.