ADDISON COUNTY — It turns out PCR tests can do more than detect COVID. Middlebury College Biology Professor David Allen and his research team use them to test deer ticks for Lyme disease.

Allen has been studying the county’s population of these creepy-crawlies since 2016. In permethrin-treated jumpsuits, he and his team of Middlebury College students spend the summers on Snake Mountain, Chipman Hill and college-owned tracts searching for deer ticks.

Covered just about head to toe in their protective clothing, the team scours the forest floor by dragging a piece of white cloth through an area they want to sample. This reveals the tiny bloodsuckers, known for their small size that makes for highly effective camouflage. 

Then it’s back to the lab to extract DNA from their samples.

From start to finish, this first part of the process takes just over half a day. It’s at this point that the ticks get their PCR tests. 

While in some states this year is projected to be a particularly potent tick season, that’s not the case for Addison County. Allen called this a “medium to high year” for the area.

Since he first started his research seven years ago, he’s observed a relatively steady deer tick population. 

“I don’t see an overall upward trend since 2016. Just like some years are high, some years are low.”

This surprised him. 

“I thought it’d be going up.” 

Allen notes the possibility that these results could be attributed to his relatively recent start date. 

“If I had started this research 10 or 15 years ago, maybe we would be seeing that increase,” he said.

Although the deer tick is a non-invasive species to North America, it didn’t appear in Vermont until roughly 30 years ago. 

In order to understand the population dynamics of the tick population Allen has been attempting to answer questions about the determinants of tick population size. 

PROFESSOR ALLEN AND his team don’t hunt for ticks individually but let them come to them. Here an assistant is able to pick up ticks by simply dragging white cloth through an area the research group wants to sample.
Photo by Todd Balfour

“I’m interested in … teasing apart what are the things that determine why we have a lot of ticks in some places and fewer ticks in other places,” he said. 

“Some of it is this role of how much of it is due to climate versus how much of it is due to the host community,” adding that this is made up of the types of animals that the deer ticks inhabit, such as mice, squirrels and their namesake, deer. 

In order to get at answers, Allen and his team collect deer ticks at varying elevations in the Green Mountains, and thus at different temperatures.  

He explains the patterns he’s observed. 

“In the Champlain Valley, like around Chipman Hill, or on the TAM, we find lots and lots of ticks, and then we go up to the Snow Bowl, and there’s … 50 times fewer ticks.” 

He said that this conclusion has been a big one. 

“We think that based on our results, it’s a combination of both that it’s colder up there, and that there are differences in the animal communities that live up there. So some of that is that in the Champlain Valley, the valley forests are just very different than the Green Mountains,” Allen said.

Now he wants to figure out what makes for a particularly bad tick year.

“One of the things I’m really interested in now is what explains why some years we have lots of ticks, and some years, we have fewer ticks.” 

This requires slightly different data. 

“And so what we’ve been doing to address that is trapping mice … we … count the mice and count the ticks on the mice.”

“Generally what we see is that when we have a big year with lots of mice, then the next year, we have a lot of ticks.”

THE CHARACTERISTICS OF the nymph-stage tick are clear under a microscope in Professor Allen’s lab. Allen notes that their small size, even smaller than a mature tick, can make them particularly dangerous.
Independent phot/Sophia Afsar-Keshmiri

Allen explained the seasonal dynamics.

 “Those (tick) larvae are feeding on mice. So when you have a lot of mice, a lot of those larvae feed, and then next year, those larvae grow up to become nymphs and adults.”

This makes for a larger population with the capability to bite humans.

“So that’s where my research is going now,” Allen said. “Getting a large enough data set of both the number of mice and the number of ticks so that we can … show this relationship between mouse populations and tick populations.”

Then it’s back to gathering ticks using the drag cloth. 

Of ticks he’s collected he said the infection rates are 25% for nymphs, which are the most dangerous stage because of their small size and greater ability to go unnoticed, and 50% for adults. 

Although the nymphs are infected with Lyme disease at half the rate of adults, Allen said the nymph stage is still the one to be most wary of. 

“(The adults) are much bigger, they’re so much easier to find, versus the nymphs, even though only 25% of them have it … there are so many of them out there.”

IN THE LAB

During a visit to Professor Allen’s lab, research assistant and Middlebury College senior Biology major Luke Van Horn pulled a set of nymph samples from 2021 from the freezer in which samples are stored at negative-80 degrees Celsius. He began the process of extracting their DNA. 

The lab still has ticks from two years ago because it was such a bad tick year. Allen said samples from 2022 were either gone or close to it.

Held in little test tubes and wrapped in paper with an ID number, the vessels were more than spacious enough for the tiny nymphs. A single one was just a speck on the white plastic container it sat in under the microscope. 

ALTHOUGH NYMPHS ARE harder to spot if you pick one up, Professor Allen notes that ticks such as this one at the adult stage produce a higher rate of Lyme-infection when they attach themselves to human beings.
Independent phot/Sophia Afsar-Keshmiri

And, although tick season is extending because of climate change, it’s not changing things for ticks in the most dangerous stage of their life cycle. 

“The nymph is most active from, like, May to August. The adult on the other hand can be found any time when it’s above freezing … so that’s where we have this really, really long tick season,” Allen said.  

But unfortunately, the nymphs are currently at their most active: “So this is the dangerous time.”

In order to stay safe, Allen urged people to wear long socks and pants, since from the ankle to the knee is the most common place to pick them up. Additionally, he notes that you can purchase repellents, such as permethrin or DEET, or even get clothing treated with the former. 

It may also prove beneficial to hike at higher elevations. 

“The colder it is up there at higher elevations … it’s generally a safer place to hike. So if you’re hiking, at Bread Loaf, generally, there’s less risk than if you’re hiking on the TAM.”

He said other spots at higher elevations include the Green Mountains, Camel’s Hump, Mount Abe, the Long Trail and Bread Loaf. 

“There’s going to be a lot fewer ticks at those types of places,” he said. 

Allen also debunked some tick-killing myths. 

“If the tick’s crawling on you, then you’re totally fine, because it hasn’t started feeding. And so it can’t transmit anything.” 

Some methods for tick-killing he suggested included flushing it down the toilet or placing it between two pieces of duct tape. 

If the tick has bitten and is attached, he said “some people burn it (the tick) or put salt on it … don’t do any of those things.” Additionally, Allen cautioned against putting Vaseline over the site. 

“Because anything that disrupts the tick will actually make it start regurgitating, and then it’s an even higher chance that it infects you.”

TRANSMISSION

Lyme disease is a bacterial infection that can give humans headaches, a high fever, joint pain, muscle aches, numbness in extremities, memory problems and other troublesome symptoms.

Ticks themselves pick up Lyme disease when tick larvae feed on an infected mouse. These future nymphs then have the ability to pass Lyme onto humans once they reach that stage.

Allen explained the transmission process. 

AFTER COLLECTION AND before DNA extraction, Professor Allen’s crew freezes ticks to minus-80 degrees Celsius in this freezer. Research assistant Luke Van Horn pulls nymph samples from the box and to begin the DNA extraction process.
Independent phot/Sophia Afsar-Keshmiri

“The bacteria actually lives in the stomach of the tick. And then once the tick starts eating, (the bacteria) senses the blood and then swims up to the salivary glands of the tick. And then the tick shoots that bacteria in with its saliva. So it’s sucking your blood and it’s also shooting in saliva.”

He suggested using a twist-off tool or dull tweezers if you are bitten. 

“You want to use more like blunt tweezers than pointy tweezers, and then get right at the base of the neck of the tick and do a slow steady pull. If you have like sharp tweezers, or you sort of jerk, then the tick can break. And then the head is left inside you. And then again, it could still … increase the chance of transmission,” he said. 

He also noted the importance of tick checks: “The longer the tick is feeding on you, the higher the chance you get infected … And that process takes maybe, like, 24 hours. So there’s a general thought that if you get it off within that first 24 hours you have a really, really low chance of getting infected.” 

In addition to pursuing his own research questions, Allen’s summer research assistants have developed one of their own.

“We’re spending some time right now looking at whether the wildlife trails that animals will use to move around in the woods, if there’s any difference in prevalence of ticks … versus just like, any random spot in the woods,” said senior Conservation Biology major Max Zeltsar. 

Additionally, Zeltsar, Van Horn and Allen’s third summer assistant, Middlebury College junior Owen McCarthy, will be presenting their results twice; once at the Vermont Disease Ecology Conference at Saint Michael’s College and again at the end of July at the Middlebury College Summer Research Symposium.