The risk of contracting Lyme disease from tick bites in Ohio is now comparable to that in regions of the Northeast United States where the disease has been prevalent for decades, according to new research by scientists at The Ohio State University.
A decade ago, a study found that only 2.4% of blacklegged ticks collected in Coshocton County carried the bacteria responsible for Lyme disease, and about 20% of white-footed mice showed evidence of prior exposure. The latest findings indicate a significant increase: up to 47.6% of ticks and as many as 60.4% of small mammals are now infected.
"And now Ohio has the same risk as those endemic regions in the Northeast. I think that is surprising to a lot of people because we think, sure, we have the tick and we have some of the hosts, but we're not Connecticut. But for some parts of Ohio, we are Connecticut at this point," said Risa Pesapane, a faculty member at Ohio State's School of Environment and Natural Resources.
Pesapane noted that while infection risk varies across Ohio, it is highest in forested areas in the eastern and southern parts of the state. However, blacklegged ticks have been reported in all 88 counties.
"I think it's really important to convey, when it comes to both personal protection and to the medical community's awareness, that you have the same chance of getting Lyme disease in Coshocton, Ohio, and other Ohio areas with the right habitat, that you do in Lyme, Connecticut," Pesapane said.
The research was published recently in the Journal of Medical Entomology.
Blacklegged ticks—also called deer ticks—are common throughout eastern U.S. states and transmit Borrelia burgdorferi bacteria causing most cases of Lyme disease among humans and dogs. They also carry Anaplasma phagocytophilum, which causes anaplasmosis.
Ningzhu Bai led this study as part of her master's thesis work at Ohio State’s Environment and Natural Resources Graduate Program. Researchers collected over 650 questing ticks and trapped more than 100 small mammals during their fieldwork. Ticks become infected after feeding on small mammal hosts carrying these pathogens early in their life cycle.
Deer play a role primarily as hosts for adult ticks seeking blood meals but are not involved directly with infecting young ticks with bacteria.
Genomic DNA was extracted from hundreds of tick samples as well as mammal tissue and blood samples to test for Borrelia burgdorferi and Anaplasma phagocytophilum infections.
"It was shocking to find that infection prevalence increased from 2.4% for Borrelia burgdorferi sensu lato to almost 50% in 10 years," Bai said. "And it was also really high for Borrelia burgdorferi sensu stricto – over 40% carried that pathogen."
Ticks tested positive for anaplasmosis-causing bacteria at a rate just over 15%. Among eight mammal species tested, white-footed mice and eastern chipmunks were most frequently infected; overall prevalence rates reached up to 60%.
"When I talk to people, I like to stress this means one out of every two ticks that you might encounter in Ohio could possibly be infected," Pesapane said.
The researchers suggest their ecological data can help target interventions such as testing acaricides (tick-killing agents) on small mammal reservoirs—a focus for future studies on Coshocton properties included in this research.
"Ecological interventions are challenging. That's why we keep promoting personal protective actions, which work extremely well," Pesapane said. She recommended using tick repellent; wearing long sleeves and pants; tucking pants into socks outdoors; performing thorough tick checks after being outside; showering; and using preventive treatments on pets.
Pesapane emphasized these precautions are increasingly necessary: "If we look from 2010 all the way to 2025, there's been a 48-fold increase in the number of Lyme disease cases in Ohio, and we are going to be considered a high-incidence state moving forward."
In addition to ongoing field studies across Ohio focused on medically important ticks, Pesapane invites public participation by mailing collected ticks for analysis through her lab or via Buckeye Tick Test—a paid service offered by Ohio State University testing submitted specimens for various pathogens including those causing Lyme disease.
She also cautioned against viewing tick exposure solely as a summer problem: "Even on days that have snow, as long as the ambient temperature is above freezing, blacklegged ticks will be seeking hosts and biting rather indiscriminately whomever they encounter," she said. "So year-round, there's a tick exposure risk."
Andreas Eleftheriou contributed as co-author on this study supported by funding from the U.S. Department of Agriculture National Institute of Food and Agriculture.
