Tuesday, September 19, 2017

Plague of Ticks: Scientists Search for Solutions

tick life cycleOn 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. The illustration for this column was drawn by Adelaide Tyrol. The Outside Story is assigned and edited by Northern Woodlands magazine, and sponsored by the Wellborn Ecology Fund of New Hampshire Charitable Foundation.


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The Adirondack Almanack publishes occasional guest essays from Adirondack residents, visitors, and those with a biding interest in the Adirondack Park.

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9 Responses

  1. M Leybra says:

    Author says, “The reasons for the increase in Lyme disease are many,” naming ‘milder winters,’ which are normally associated w/ ‘climate change’ attributed to human actions & forest fragmentation caused by expanding human habitat, all pretty much one & the same. “Disease ecologist Richard Ostfeld advocates for biodiversity — A diverse woodland…” & ecologist Felicia Keesing predicts “a bad year for Lyme disease” bc of (cyclical) high mouse populations. One lyme tick control by man is using bait boxes to dose mice w/ fipronil, an insecticide that disrupts insect’s central nervous system. Any studies on mammals, hawks, owls etc., the ‘biodiversity’ who consume the abundance of dosed mice? Or the dosed-in-turn ticks consumed by possums & songbirds? Or the effects on the biodiversity of animals who consume forest vegetation that’s been treated w/ a spray containing unnatural amounts of a fungus? Who knows, All this is not the purview of the CDC.

  2. Charlie S says:

    “we poison mice and rats daily..”

    Yes we do and I will never forget the time a screech owl was brought to me that was in a very disturbed state….it was incapacitated its body was jerking violently, etc. My conclusion was that it went after a mouse that was poisoned and bit into it. My friend Mercedes let it be know that they were putting poisons out in her neighborhood. How sad and what a horrible way for that screech owl to have gone. Once again because we humans are always looking for a quick fix we overlook the negative results that can come from them as has been proven over and again, ie… we are not futuristic in the decisions we make.

  3. Chris Maron Chris Maron says:

    Controlled burning and allowing natural fires to burn while not endangering houses,is likely an effective way to reduce tick populations. I have noted that in burned areas, the tick populations are greatly reduced.

    • M Leybra says:

      “Natural fires” started by man to burn up forests to reduce human tick encounters while being careful not to burn up any human homes that have been built in forested areas. Say you’ve noticed “tick populations are greatly reduced” in burned areas. What else have you noticed greatly reduced, song birds, turtles, snakes, a butterfly or any other signs of life that was able to flee? As long as human ego rules the earth, this century will witness the last great extinction, all that remains of diversity of biological life outside of ourselves.

  4. Tom French says:

    There is a human vaccine for Lyme, but production was discontinued in 2002 due to a lack of demand. Read about it straight from the CDC website:

    https://www.cdc.gov/lyme/prev/vaccine.html

    Call your congressional representatives.

  5. Wally Elton Wally says:

    Prior to about 1975, was Lyme basically absent? Or just not recognized? One causal theory not mentioned has been that chestnut blight resulted in a huge increase in the number of oaks in eastern forests, which yielded many more acorns, which in turn created a larger population of mice to host ticks.

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