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2021 drought impact on Minnesota tick numbers unclear at summer peak

Regardless of how bad individual years are, the Minnesota Department of Health is not as concerned with year-to-year trends as it is concerned with the big picture over time, said agency tick disease specialist Elizabeth Schiffman.

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Ticks are vectors for diseases, such as Lyme Disease, erlichiosis and anaplasmosis.
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ST. PAUL — Forecasting tick populations is an inexact science, but with last year’s severe drought in Minnesota, some public health officials predicted there would be fewer Lyme disease-carrying deer ticks in wooded areas across the state in 2022.

But whether or not that will be the case still remains unclear as the state enters its peak season for tick activity, which typically begins in May and extends to July. Further muddying the picture? The state's protracted, soggy end to winter may have led to a sudden surge of deer tick activity when conditions became more favorable, said University of Minnesota public health entomologist Jon Oliver.

“This year, we had a really late spring and I think that sort of pushed all of the adult deer ticks to kind of come out at once,” he explained. “So there was a while there where really there were just a ton of adult deer ticks out.”

Researchers with the U of M search for ticks by dragging a cloth through the wooded brushy areas where deer ticks typically live, Oliver said. In spring 2021, researchers dragged a cloth for 2 hours and picked up 30 adult deer ticks. This spring, one hour of dragging netted closer to 60, Oliver said. This time of year is typically the peak for the immature or nymphal stage deer ticks, though right now it’s not entirely certain just how many there are in the environment. Oliver said he’d be going into the field to search for them and would soon have a better idea.

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The results of the initial spring search may not end up reflecting the overall tick picture this year. The Metropolitan Mosquito Control District conducts tick surveillance in the seven-county Twin Cities metro area and found that so far there have been fewer deer ticks — possibly because of the drought. Anecdotally, there has been a surge in the number of the larger wood ticks, also known as the American Dog tick, mosquito control district spokesman Alex Carlson said. However, public health officials do not keep as close track of the larger tick as it does not typically harbor serious diseases in Minnesota and is not known to carry Lyme disease.

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Regardless of how bad individual years are, the Minnesota Department of Health is not as concerned with year-to-year trends as it is concerned with the big picture over time, said agency tick disease specialist Elizabeth Schiffman.

“We usually don't just look year to year to really be able to see what's happening because when we look at our numbers over time, there are high years and there are low years,” she said. “We definitely have seen an expansion over time, kind of gradually moving … here in Minnesota, more toward the north and west, filling in the top two-thirds of the state.”

Deer ticks and Lyme disease were more of a problem in the southeastern corner of the state in the 1990s but have consistently spread across Minnesota in subsequent decades, Schiffman said.

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Derosier, Alex

Decades ago, the state reported hundreds of cases each year, but by the late 2010s it would often be over 1,000. Schiffman and Oliver agree that our warming climate could very well be a contributing factor as milder winters allow more ticks to reach farther north. But human development and land-use changes leading to fragmented forests is another major driving factor, both said.

About one in three adult ticks and one in five tick nymphs carry the bacteria that causes Lyme disease, though Oliver with the U of M said the smaller nymphal ticks can pose a greater risk because they can be harder to spot.

Lyme disease symptoms typically start with a distinctive bulls-eye rash at the site of the bite within three to 30 days, followed by fever, muscle and joint pain and fatigue. Lasting effects include chronic joint pain, weakness and fatigue. The disease is treated with antibiotics, with earlier treatment generally having greater success.

Experts recommend regularly checking your body for ticks every 24 hours if spending time outdoors, especially after entering wooded areas. A deer tick must be attached to your body for longer than that period in order to pass along the bacteria that causes Lyme disease.

MDH also recommends doing the following to avoid tick bites: Avoiding wooded, brushy areas from mid-May through mid-July; Walking in the center of trails to avoid picking up ticks from grass and brush; wearing long, light-colored clothing to protect you from ticks and make them more visible if they are on you, and using a tick repellent with up to 30% DEET or permethrin-based repellents for clothing.

Alex Derosier covers Minnesota breaking news and state government for Forum News Service.
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