Grace Hummell, a University of Maryland graduate school student, plans to wade into tall grasses and scour the edges of Howard County’s woodlands this fall for the common white-footed mouse.
From woodlands to neighborhood backyards, mice are everywhere, even if usually unseen. But Hummell aims to capture dozens of them as part of a five-year effort by U-Md. and other researchers to figure out how best to reduce tick populations and, they hope, Lyme disease. Contrary to the popular belief that deer are the primary source of the disease spread by ticks, researchers say, it is mice that usually first infect young ticks with the bacteria that causes Lyme.
Once the young ticks feed off the mice, they will drop off, grow into adults and then attach to a larger mammal such as a human or a deer on which they will continue to grow and reproduce.
“The science is fuzzy,” said Jennifer Murrow, a wildlife ecologist and an assistant professor in U-Md.’s Department of Environmental Science and Technology. “What we think is the primary role of the deer is to maintain populations.”
The Howard County work Murrow and Hummell are participating in is part of a much larger Lyme-disease prevention study being done in areas across the country, led by the Agriculture Department’s Agricultural Research Service. The Centers for Disease Control and Prevention is participating along with U-Md. and the University of Massachusetts.
More than 300,000 people contract Lyme disease through tick bites each year. The disease is concentrated on the East Coast from Maryland to Maine, and there were 1,866 confirmed and probable cases of Lyme in Maryland in 2016, according to the CDC.
Lyme disease gives people fever, headaches, fatigue and a skin rash, according to the CDC. If it is not treated, it can lead to an infection in the joints, the heart and the nervous system.
With the cases of Lyme disease increasing over the past 25 years, researchers have been turning their attention to prevention, including efforts to find a vaccine and attempts to reduce the population of ticks carrying the bacteria.
The effort in Howard County is decidedly low-tech.
Murrow, working with Hummell, puts out traps for mice and deer. The trap for mice is a mere bait box, developed by the CDC and sold by a private company, that is filled with cotton or something to eat. When a mouse enters to get the bait, it rubs its back against the box.
It is “like walking through a little mouse carwash,” Murrow said. “They get treated with a pesticide, an oily substance that gets on their fur.”
The hope is that the pesticide kills the ticks, much the way dogs and cats are treated for ticks by pet owners. Murrow said they are testing how effective the bait boxes are at reducing the tick population in a large area.
Andrew Li, an entomologist and principal investigator with the Agricultural Research Service’s Invasive Insect Biocontrol and Behavior Laboratory in Beltsville, said they are also using a device for deer, called a “four poster,” that attracts deer with bait. The deer then has to rub its neck and ears against a roller that looks much like a paint roller, except that it carries a pesticide to kill ticks.
“If we put them out, could we reduce the likelihoods that mice have ticks?” Murrow said.
After Hummell captures the mice, she removes ticks from them with tweezers and then places a tiny VHF radio tracking collar around their necks. The mice are released and tracked over 10 weeks to determine whether tick numbers are reduced.
The ticks plucked off the mice are counted and tested. The results of the first capture this spring were surprising.
“About 60 percent of mice they captured carried this bacteria,” Li said.
The mice were captured near four Howard County parks — Cedar Lane Park, the Middle Patuxent Environmental Area, Centennial Park and Rockburn Park.
The numbers of ticks on each mouse can be astounding, according to Hummell, who has picked a dozen to as many as 60 off the ears of a small mouse.
Besides the bait boxes and the four posters, the study is testing a fungal spray that does not harm the environment but kills ticks.
Li said that, with work at several sites over five years, the study’s conclusions could help communities fight Lyme disease by determining the best ways to reduce the number of ticks, particularly in areas that might be hot spots.
Working with government agencies, he said, neighborhoods and communities could come together to put out bait boxes, fungal treatments and four posters to try to limit the number of ticks infected with the bacteria that causes Lyme. Many of the tools are already available commercially, so Li sees the study as a way to refine the most effective practices.
“By the end of the five-year project, we will have a very good idea of what control measures work,” Li said.
In the meantime, Li and Murrow said, residents can protect themselves by wearing long pants, spraying their clothing with DEET and checking themselves for ticks soon after they get inside.