A Plague of Ticks: Scientists Search for Solutions

A Plague of Ticks: Scientists Search for Solutions

Illustration by Adelaide Tyrol

On a hike this spring, we walked through a clear-cut area with tall grass and brambles. Afterwards, our pant legs were crawling with black-legged ticks (Ixodes scapularis), also known as deer ticks, the kind that carry Lyme disease. Scientists with the Vermont Department of Health recently examined over 2,000 ticks and found that 53% of black-legged ticks tested positive for Lyme disease. A small percentage of the ticks carried pathogens that cause anaplasmosis or babesiosis, two other tick-borne diseases that can make people gravely ill.

Understanding the two-year life cycle of the black-legged tick can help prevent Lyme disease. In the spring of the first year, tick larvae hatch from honey-colored eggs in the leaf litter. The six-legged larvae, about the size of a poppy seed, soon seek their first blood meal. The larvae may become infected with the bacterium that causes Lyme disease through this blood meal; it all depends on what kind of animal they find as a host. If it’s a white-footed mouse, they’re very likely to contract the Lyme spirochete. If it’s a chipmunk or shrew, they’re somewhat likely. If it’s a squirrel or a larger mammal, they probably won’t.

After feeding, the larvae drop off into the leaf litter and remain dormant until the next spring. In the spring of year two, these larvae molt into eight-legged nymphs, the size of a pinhead, and seek another blood meal. While most feed on mice and chipmunks (and have another opportunity to contract Lyme disease), pets and humans may become unsuspecting hosts.

In late summer and fall, the adult ticks, now the size of an apple seed, attach to large mammals, usually deer, where they feed and mate. People and pets are susceptible to picking up ticks at this time, although at this stage they are easier to see and feel. After this last blood meal, the females lay up to 3,000 eggs and the two-year life cycle begins again.

Lyme disease was first recognized in the US in 1975, after an unusual outbreak of arthritis in Lyme, Connecticut. Today, the Center for Disease Control and Prevention (CDC) estimates there are over 300,000 cases in the US every year. A CDC map of Lyme cases shows that most are in the Northeast, mid-Atlantic, upper Midwest, and West Coast. Vermont, Maine, New Hampshire, and New York are all considered high-incidence states and the number of cases of Lyme has risen in recent years.

The reasons for the increase in Lyme disease are many. Climate change is probably part of it. Milder winters have allowed ticks to expand their range and emerge earlier in the spring, as well as leading to a surge in the deer and mouse populations that feed them. Forest fragmentation has contributed to an increase in mice, which thrive in small patches of woodland, while their predators need larger forests to survive. In his groundbreaking 2011 book, Lyme Disease – The Ecology of a Complex System, disease ecologist Richard Ostfeld of New York’s Cary Institute advocated for biodiversity — managing our landscapes for ecological health to promote human health. A diverse woodland is home to many other animals besides mice and deer that attract ticks but don’t infect them. Some, like opossums, even eat ticks.

Ostfeld and Bard College ecologist Felicia Keesing predicted that 2017 would be a bad year for Lyme disease because of high mouse populations last year, due to an abundant mast crop in 2015. In some areas, said Ostfeld, 90 percent of mice harbor Lyme disease, which translates into correspondingly high infection rates for ticks.

Ostfeld and Keesing are searching for methods to control ticks and Lyme disease. Their Tick Project, in partnership with the CDC, New York Department of Health, and others, is in the second year of a five-year study in Dutchess County, New York, which has one of the nation’s highest incidence of Lyme disease. The study will determine whether two tick control methods, used separately or together, can reduce the number of cases of Lyme disease in twenty-four neighborhoods. This spring, small bait boxes that attract rodents were placed in the study area. When an animal enters the box, it receives a dose of fipronil, the active ingredient in many tick treatments used on dogs and cats. The other tick control method in the study is a spray containing a fungus that occurs naturally in northeastern forest soils and has been shown to kill ticks. This fungal spray was applied to vegetation in the study area. If these methods are found to be effective, they are already commercially available and others could begin using them immediately, offering hope in the battle against ticks and Lyme.

Susan Shea is a naturalist, conservationist, and freelance writer who lives in Brookfield, Vermont.

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Discussion
  1. Robert Roggeveen → in West Hartford
    Sep 18, 2017

    A timely reminder to take extra precautions when in the woods. Thank you for this article.

  2. K Leach → in Boston MA
    Sep 20, 2017

    Lyme disease is another human health issue worsened by current human behavior, i.e. unbridled development. Deer hunts are a false solution since human hosts will fill the “large mammal” void due to a smaller deer population.

  3. Asheley Kapelewski → in Poultney, VT
    Sep 21, 2017

    I spent time hiking in the protected forests of the northern Adirondacks this summer, and in the old growth forests that have been saved from logging for over a hundred years, there is no tick problem. No signs warning you of ticks in on all the trailheads like we have in Northern New England where constant logging is the norm. I went thru wet Meadows and scrubby fields where I would have been covered with ticks if I were in NH or VT. Plenty cold where I live, doesn’t slow the ticks at all. The habitat fragmentation is what gives this plague the edge.

  4. Dave Mance → in Corinth, VT
    Sep 22, 2017

    I agree with you, K, that deer hunts are a false solution in most areas, simply because they’re (the deer populations are) so elastic. If the habitat is good, deer will recolonize an area. In an experiment along these lines conducted in a town in New Jersey in the early 2000s, the town removed roughly half of its deer herd, and it appeared to have no effect on the number of ticks. But it’s not accurate to say that humans would fill the void left by deer. It’s not so much the blood meal that makes deer crucial to the tick’s life cycle, it’s the fact that they serve as a kind of singles bar that facilitates tick mating. For humans to play that role we’d have to be alright with ticks crawling all over our bodies, mating, feeding on us, falling off. I can’t imagine anyone being alright with that.

  5. HRCJON → in Maine
    Oct 01, 2017

    Deer hunts are a critical and important issue. Research on island populations and other areas shows low deer density reduces infected tick density. Nothing false about it. The key is that you have to get to low densities. A one time or temporary reduction does nothing as deer are amazing at reproducing.

  6. Nod Nostrebor → in Limestone
    Oct 04, 2017

    I had a deer tick on me for 24 hours. I’m 67 and I sure didn’t want to get Lyme disease. So I went to see my doctor right away when I found it.

    An antibiotic prescription, just one pill took care of the problem.  Just one pill, because I acted quickly.

    My suggestion is, don’t take the chance of getting Lyme.  Go see your doctor and take that one antibiotic pill.

  7. Susan Shea → in Brookfield, VT
    Oct 06, 2017

    While doing the research for this article, I learned that high mouse populations seem to have more effect on tick numbers than deer populations, and that deer control hasn’t had much impact.

  8. Chas Goke → in Central Maine
    Oct 09, 2017

    Got a call from my son said he was week and blacking out. Rushed him to hospital. His heart ekg was all over the place, even completely stopping. Locals didn’t know what it was, rushed him to the big city hospital to the cardiac unit. Cardiac surgeon took one looks and diagnosed lyme immediately administered strong anti bionics. Blood tests confirmed later. This doc saved his life. We had no idea lyme could do this. Everyone needs to up there awareness all over the country, We are getting the word out everywhere we can.

  9. HRC → in Maine
    Oct 09, 2017

    I don’t think you have done enough research. I got here via George so here’s his link on the issue. Every island that has done deer elimination has seen a different and positive improvement in the situation. And numerous studies show deer population to infection rates. http://georgesoutdoornews.bangordailynews.com/2016/10/28/environmental-issues/monhegan-killed-all-its-deer-and-eliminated-lyme-disease/

  10. Dave Mance → in Corinth, VT
    Oct 11, 2017

    In response to your comment, HRC, yes, if you kill all the deer on an island and don’t let any more back on, Lyme rates drop. But this doesn’t really apply in any practical way to mainland areas, where there isn’t a natural barrier that prevents reestablishment and (thankfully) the idea of deer elimination is a non-starter.

  11. Michael Herrick → in Red Hook, NY
    Oct 11, 2017

    Here in Red Hook, Dutchess County, we’ve had an unusually tick free season - from spring through fall.  We have a dog and cat and we spend a lot of time walking our property - 35 acres of woodlands and meadows (with trails).  Few ticks on pets and no ticks on my wife or self.  I’m guessing it was the unusually warm winter with the heavy late snow in March.  We do have more chipmunks than I’ve ever seen before.

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