Ticks find hosts by detecting odors while in a "questing position" with outstretched legs.
Wisconsin is considered high-risk for Lyme disease almost statewide. Follow some easy steps to keep your family safe this summer season.
Kathryn A. Kahler
Tami Ryan, DNR's wildlife health section chief, remembers that when she was hired in the early 90s, if someone from southeast Wisconsin was diagnosed with Lyme disease, it was likely they contracted it while traveling. At that time deer ticks – which carry the bacteria that cause the disease – were only found in areas along the Mississippi River in the northwest corner of the state.
"Now they are statewide," Ryan reports. "Wisconsin is now one of the highest risk areas in the country and the common conclusion that ‘you got Lyme disease while vacationing' is no longer being made."
A recent study and map puts Wisconsin, parts of eastern Minnesota and northern Illinois in the same high-risk category as eastern states like New Hampshire, Massachusetts and Connecticut, where the disease was first recognized in 1975. Reported cases of Lyme disease in Wisconsin have increased more than tenfold, from 329 in 1990 to 3,498 in 2010. Because the disease is underreported, these numbers may only represent 10 to 20 percent of actual cases.
It's all about the tick
Knowing something about the disease and how it spreads can help you take steps to prevent it. The disease is caused by a spiral bacterium, or spirochete, called Borrelia burgdorferi, and is transmitted to humans by the bite of an infected deer tick, Ixodes scapularis. Deer ticks, also called black-legged ticks, are about half the size of dog ticks. In the four stages of the tick's life cycle, they feed on various blood sources, including mice, birds, deer and humans. Humans are the only ones to contract the disease; wildlife hosts simply provide the blood source and suffer no harm.
In order for the immature nymphs and adults to get the blood they need, they climb blades of grass or other vegetation and wait for a host to walk by. When one comes near, the ticks can detect odors from the host – like carbon dioxide, ammonia and lactic acid – and assume a "questing position," clinging to the grass with two pairs of legs while holding their front pair outstretched. When the host brushes against the grass, the tick grabs hold and either attaches to the skin or wanders the body in search of a thin-skinned area to attach and feed. That's when the bacteria in their stomachs can be transmitted to a human host.
The tick needs to be attached for 24 to 48 hours before the bacteria are actually transmitted. It is key to remove the tick within the first 24 hours to prevent infection.
Once infected, a person can have a range of symptoms, and if untreated can experience late stage problems months or years after the initial onset. Early symptoms include a skin rash – sometimes in the distinctive bull's-eye shape known for the disease – and flu-like symptoms like headache, fever, chills, fatigue or stiff neck. Later stage symptoms include arthritis, neurologic and cardiac problems.
The disease is highly seasonal, with over 80 percent of Wisconsin cases reported from May through August. That's when most nymphs (which are about the size of a pinhead) are feeding and when most people are enjoying the outdoors.
Follow these steps to protect you and your family
Whenever you plan outdoor activities this summer, these simple steps can help reduce your risk of getting Lyme disease:
Beyond that, there may be steps you can take to make your property less attractive to deer tick hosts (specifically, white-footed mice, birds and deer), or at least keep them away from your primary activity area, especially if your property is rural and you have woodlots.
"Essentially, you could remove the understory around the perimeter of your residence," suggested Ryan. "Put that woody edge further away from your primary activity areas. Also, consider planting vegetation that deer don't find palatable and would avoid. These are things you can do to keep small rodent and bird populations along your yard edges and away from primary activity areas."
You can also ask landscape specialists to incorporate tick management concepts into your design. But attempting to manage host species as a means of targeting the disease is tricky and something that needs further study.
"At the end of the day personal protection is the first and foremost preventative measure," says Ryan. "There is much still to be learned on landscape management and other practices."
Kathryn A. Kahler is a staff writer for Wisconsin Natural Resources magazine.