When Susan Paskewitz searched the UW Arboretum two years ago for immature deer ticks, the kind most likely to infect people with Lyme disease, she found 32.
Last year, during the same amount of sampling at the same 17 sites in the Arboretum, she found 592.
“We’re really seeing them move into areas in Madison, in Milwaukee and in other parts of southeast Wisconsin,” said Paskewitz, a UW-Madison professor of entomology.
Lyme disease, a bacterial infection that in Wisconsin was mostly confined to the northwest part of the state years ago, has become a statewide problem. More than 3,200 cases were reported in people last year, a tenth of what health officials believe actually occurred.
Other diseases carried by deer ticks, such as anaplasmosis and ehrlichiosis, also appear to be on the rise. Like Lyme, they can cause fever, chills, fatigue, muscle pain and severe headache. All of the conditions can be treated with antibiotics, but they sometimes cause serious complications.
“Anyone can get a tick-borne disease,” said Diep Hoang Johnson, vector-borne disease epidemiologist with the state Department of Health Services. “It’s all over Wisconsin ... It can be in your backyard, even in the cities.”
Zika virus, spread by mosquitoes, has been getting a lot of attention this year because an outbreak in Latin America and the Caribbean was accompanied by serious birth defects. But it’s unlikely anyone will be exposed to Zika in Wisconsin this summer, health officials say.
Mosquitoes in the state can carry West Nile virus and other potentially serious diseases, but reports of human cases are relatively rare.
People concerned about bug bites making them sick should especially watch out for deer ticks, also known as blacklegged ticks, officials say. The ticks started circulating in April, typically peak in June and surge again in October.
Wood ticks, or American dog ticks, are also common in Wisconsin but aren’t known to spread disease here.
To prevent tick-borne diseases, people should avoid wooded, bushy areas or wear long pants and long sleeves and use repellent, health officials say. After being outdoors, they should check for ticks and remove any with tweezers.
Paskewitz and others from her lab visit more than 30 areas in the state to look for deer ticks. In the Madison area in recent years, they have discovered the ticks in Sandburg Woods on Madison’s Far East Side, UW-Madison’s Lakeshore Nature Preserve and the Pheasant Branch Conservancy in Middleton.
At Sandburg, 19 percent of immature ticks were infected with Lyme. Sampling at Owen Park on Madison’s West Side hasn’t turned up deer ticks, Paskewitz said.
In the Milwaukee area, the researchers have found deer ticks at Doctors Park, Cedarburg Bog, Muskego Lake and Richard Bong State Recreational Area. The ticks weren’t tested for Lyme.
In the Arboretum, where Paskewitz first discovered deer ticks in 2010, she and others from her lab are studying two ways to reduce the population of deer ticks and the percentage of them infected with Lyme.
Working in 17 half-acre plots in the Arb’s Lost City Forest, the researchers are removing buckthorn from some of the areas to create dry environments inhospitable to ticks.
In other areas, they’re targeting white-footed mice, a major source of blood for deer ticks. They soak cotton balls with insecticide, place the balls in PVC pipes and leave the pipes in the forest. Mice use the cotton balls to make nests, and when ticks get on the mice the insecticide kills them.
“It’s a bit like treating your dog with Frontline,” Paskewitz said.
In some plots, the researchers do both activities. In others, they do neither, so they can compare the effect.
Monthly, from May to August, they trap mice and chipmunks, and drag white sheets across parts of each area, to count ticks and test them for Lyme.
Last year, in the sites where buckthorn was removed and/or cotton balls were used, about 4 percent of immature ticks tested were infected with Lyme. In the untouched areas, it was 12 percent.
Overall, the figure was 8 percent. Statewide, it ranged from 5 percent in the northeast to 32 percent in the northwest.
The Arboretum plots where both activities were done also had about half the number of immature ticks last year as the areas that were left alone, Paskewitz said.
“It looks like we have reduced the risk of encountering an infected tick significantly,” she said.
The percentage of adult ticks infected with Lyme typically is about double that of immature ticks. But the scientists pay less attention to the adults because people generally can spot them and remove them from their bodies quickly enough to prevent infection.
It’s the immature ticks, called nymphs, that are the real troublemakers. “They’re so tiny, they look like a little freckle,” Paskewitz said. “You don’t feel them.”