Deer ticks in Wisconsin and the diseases they carry
One enduring myth about ticks is that these little bloodsucking creatures hang around on tree branches and leaves, waiting to drop down on an unsuspecting feast. Ticks don't dive-bomb their intended meals, but they do engage in behavior called "questing" where they sit on vegetation with limbs extended, ready to climb on a host that brushes past them.
Wisconsin is home to a handful of tick species, but one stands out: the deer tick, which is responsible for infecting people with the bacteria that cause Lyme disease. First spotted in north-central Wisconsin in 1965, deer ticks became increasingly common around the state in the 1980s, '90s and 2000s. Over the same period, Lyme disease spread as well, turning Wisconsin into one of the nation's hot spots for a growing epidemic.
Susan Paskewitz is a professor in the University of Wisconsin-Madison Department of Entomology who studies diseases transmitted by arthropods like mosquitoes and ticks. Her work in the UW Medical Entomology Laboratory includes research on Wisconsin ticks and tick-borne diseases, particularly factors that help spread Lyme disease among deer ticks and their other wildlife hosts. She discussed ticks and the diseases they carry in a Wednesday Nite @ the Lab lecture on the UW-Madison campus on Aug. 5, 2015, that was recorded for Wisconsin Public Television's University Place.
With Lyme disease continuing to spread around the state, Paskewitz's research has focused on the relationship between wood ticks, the animal hosts that carry pathogens, and the landscapes they inhabit. "The tick distribution is very associated with the greener, the more forested parts of Wisconsin. And that's also where we also see a lot of the Lyme disease," she said.
The first defense against Lyme disease, though, is limiting exposure to deer ticks in the first place. Paskewitz recommends standard precautions for minimizing the chance of being bitten by ticks while spending time outdoors, including using insect repellent, wearing long pants and boots, and even treating clothing with permethrin.
For people who do get bitten by deer ticks, it's important to remove them as soon as possible to reduce the risk of transmission.
"The ideal way to get them off is to just take a nice sharp pair of tweezers, put tweezers down as close to where the tick's mouth parts are into your skin as possible," Paskewitz said. "Slowly exert some backward pressure on it. You don't want to yank it out because you'll leave the mouth parts in your skin. So what you are really trying to do is get the tick to decide it wants to leave, fold up its tent, and pull itself out."
Of course, many thousands of people in Wisconsin acquire Lyme disease every year, and those cases are widely underreported by health care providers. For people who may be infected, Paskewitz urges vigilance. Along with a telltale bull's-eye rash, several other symptoms can indicate Lyme disease, including fever, fatigue and muscle aches.
"It just feels like you got the flu," she said. "You should go to your doctor right away and arrange to get some antibiotic."
- Ticks are a type of arthropod that have eight legs, and are therefore arachnids, more closely related to spiders than six-legged insects. The species commonly called the wood tick is more specifically named the "American dog tick" and its scientific name is Dermacentor variabilis. The species commonly called the deer tick is more specifically named the "Black-legged tick" and its scientific name is Ixodes scapularis.
- Wood ticks are abundant in open meadows and other grassy areas. On the other hand, deer ticks are more common in wooded areas and along their fringes.
- Deer ticks go through multiple stages of life after hatching, developing from larvae to nymphs to adults, with meals of blood required at each step. Females tend to consume far more blood than males. In fact, female ticks can take in 200-600 times their own body weight in blood from their hosts. This sustenance is necessary for egg production, and each female can produce between 1,000 and 3,000 eggs depending on the size of the meal.
- Deer ticks have been found to feed on a wide variety of birds and mammals, including white-tailed deer, white-footed mice and deer mice, chipmunks, red-backed voles, opossums, skunks, raccoons, foxes, wolves, dogs, cats and, of course, humans.
- Lyme disease is caused by multiple bacteria in the Borrelia genus. The primary species found in the U.S. is Borrelia burgdorferi; it's of a type called a spirochete, so named for its coiled shape.
- On average, about 22 percent of deer tick nymphs in Wisconsin have been found to be infected with Borrelia burgdorferi. The infection rate for adults is about twice as high, around 40-45 percent. In some locations, though, researchers have found infection rates as high as 75 percent of the tick population.
- The number of deer ticks in specific areas of Wisconsin can vary widely by area, by landscape, and by forest type. Researchers have not found any relationship with the numbers of white-footed mice or white-tailed deer in any given areas.
- In 2013, researchers from the Mayo Clinic discovered a new bacteria species in the Spooner area that is carried and transmitted by deer ticks. Called Borrelia mayonii, the bacteria causes an infection that is detected by the same diagnostics used to identify Lyme disease and responds to the same antibiotic treatments.
- Along with Borrelia bacteria, deer ticks in Wisconsin can harbor and transmit several other pathogens, including Anaplasma bacteria, Ehrlichia muris bacteria, the Powassan virus, and Babesia microti, which is a type of protozoan parasite. Of the diseases caused by these organisms, anaplasmosis is the most common in Wisconsin, with hundreds of cases diagnosed and reported each year.
- One species emerging in Wisconsin is the Lone Star tick, which is named for a distinctive marking on its body. Its scientific name is Amblyomma americanum, and its historical range is across much of the eastern U.S. The Lone Star tick transmits multiple species of bacteria that cause disease in humans, and its bite can also trigger a meat allergy among victims.
- Paskewitz on the difficulties of removing feeding ticks: "If you look at these mouth parts, they're a little bit like fishing hooks, right? They're barbed, and so that barb makes it much harder for you to just smoothly pull that ... out with a forceps once it's actually embedded. The other amazing thing that these ticks do is they secrete a little bit of a compound that turns into a hard cement right inside your skin. And that hard cement can also kind of makes it really hard for you to dislodge them and pull them back out."
- Paskewitz on one way not to remove ticks: "Some people say you should light a match and then take the hot match and touch it to the back of the tick. … Specialists don't recommend this. The reason why we think this is a bad idea is because when you touch it with the hot match, it may regurgitate into you. You've shocked it, right? So the contents of its gut, actually, where the bacteria are that can make you sick, might actually be directed into your system."
- Paskewitz on the role of wildlife in the transmission of pathogens that cause Lyme disease and other maladies: "The animal part of this equation, the wildlife part, is really important because that's where the ticks are picking up the disease organisms, right? This is where they're getting infected with something that they can then subsequently transmit to you."
- Paskewitz on the bull's-eye rash associated with some cases of Lyme disease: "If you're lucky, you'll get the bull's-eye rash, which is very diagnostic and occurs at the site of the tick bite. There are different estimates, though, in terms of how many people actually get the bull's-eye rash. CDC says maybe 25 percent of people don't, and other studies suggesting that maybe 40 percent of people don't get the rash. And the problem, which I can attest to, is these ticks are very small and their favorite place on my body, actually, turns out to be my head. … Suppose I miss it? And I get the bull's-eye rash on my head, I'm not going to see it, right? Or if you get one in the middle of your back? You can imagine that would be a very easy thing to miss. So not everybody gets the bull's-eye rash, and it's not always in a place where you can easily see it."
- Paskewitz on treatment for tick bites: "There are some professional guidelines that inform physicians in terms of what you should do if a patient comes to you with a tick bite but not sick yet, they have no symptoms of disease. So should you wait for symptoms? Or should you give them a big dose of antibiotic prophylactically to try to head off any infection? And the rules that have been determined are: You got to make sure it's a deer tick. The tick needs to have been attached for 36 hours because before 36 hours the chances that they've actually managed to transfer the pathogen to you are much less. And importantly, more than 20 percent of the nymphs in an area need to be infected."
- Paskewitz on the growing incidence of Lyme disease: "Some of it I'm sure has to do with stronger surveillance at the county level because this data actually comes from county public health, who are reporting to the state what the local doctors are telling them about the number of cases that they're identifying. So part of it is that, but part of it also is due to the spread of the ticks into new regions and also increases in the population and the infection rates in those regions."
- Paskewitz on the growing incidence of anaplasmosis: "[W]e are actually a hot spot in the whole country. So, you know, for Lyme it's us and the Northeast, and there are a lot more Lyme cases in the Northeast. For this one, actually, Wisconsin and Minnesota are the hot spots. We have 50 percent of the cases in the whole United States. And again where do you find this? Well, it's in the same kinds of places where you'd expect. The same places where Lyme is very abundant."
- Paskewitz on the increasing frequency of Lone Star tick sightings in Wisconsin: "I thought there was probably a lot more going on than we realized. ... [W]e're getting lots of reports now and actual sampling, especially in the southern part of the state. Dane [County] is probably a hot spot because there are a lot of people here who know to contact the university when they see something unusual, and because we also do a lot of work here and we picked them up a number of times at our site.
This report was produced in a partnership between Wisconsin Public Radio, Wisconsin Public Television and the University of Wisconsin Cooperative Extension. © Copyright 2017, Board of Regents of the University of Wisconsin System and Wisconsin Educational Communications Board.