Black-Legged Ticks Are Now Widespread In Vermont, And Half Carry Lyme

Jun 17, 2015

It's summer and people are enjoying the great outdoors. But there’s bad news about ticks and Lyme disease: Black-legged ticks have been slowly moving northward, and it’s safe to assume they’re everywhere in Vermont now, even in the Northeast Kingdom.

That's according to Alan Giese, an expert in disease-carrying ticks at Lyndon State College.

“They're there,” Giese told Vermont Edition. “They're just there at very low levels, so they're sort of undetectable. We don't find them very often.”

Giese's team has captured and tested about 800 ticks in Vermont in the last few years. Half of them are carrying borrelia, the bacteria that causes Lyme disease. Giese says that “even in areas where we have really low densities of ticks, the prevalence of Lyme is still hovering right around 50 percent. So even if you're in an area where ticks aren't very common, if you do end up with one, our data suggests that you should still be very concerned about Lyme disease.”

The CDC reports that Vermont has the highest rate of Lyme disease in the country, close to 10 times the national average.

Explore the data: Check out Lyme On The Rise, a special VPR data visualization of Lyme disease in our region.

“It has to do with environment and exposure to ticks,” says Dr. Jeffrey Parsonnet, an infectious disease specialist at Dartmouth College. “There's not a lot of Lyme disease in Manhattan. But when people are living in rural areas, as we are, and as the tick and the infected ticks become more prevalent, that's a setup for a high incidence of Lyme.”

"Even if you're in an area where ticks aren't very common, if you do end up with one, our data suggests that you should still be very concerned about Lyme disease." - Alan Giese, Lyndon State College

Experts recommend taking precautions like wearing long pants when you’re outside and calling your doctor if you think you’ve been exposed to a tick bite. Here's a list of other precautions:

  • Avoid long grass and brushy areas.
  • Wear long pants and tuck them into your socks when you’re out in the woods and fields.
  • Check for ticks after being inside, paying special attention to crevices like the backs of knees and elbows. Don’t forget to check your hairline.
  • Pull ticks off when you find them, taking care not to burst their bodies.
  • Call your doctor if you think you’ve been exposed to a tick bite, especially if you see a rash in the affected area.

Answering Questions About Ticks and Lyme Transmission

Since we originally posted this story we’ve gotten a lot of inquiries for more details about ticks and Lyme disease, so we’re answering some of your questions here.

Q: How many kinds of ticks are there in Vermont?

The Vermont Department of Health reports on its website, “Ticks have become quite abundant in many parts of Vermont. Thirteen different tick species have been identified in Vermont, but only four are known to carry pathogens such as bacteria, viruses and parasites that cause disease in humans.”

Q: Which ticks transmit Lyme disease?

From the Vermont Department of Health: “The deer tick (Ixodes scapularis) is also known as the black-legged tick. These ticks may transmit the organisms that cause anaplasmosis, babesiosis, Powassan virus and Lyme disease. Ticks acquire these organisms by feeding on infected small animals, and then spread disease to other mammals while taking a blood meal.”

Q: What kinds of ticks is Dr. Giese testing?

Alan Giese: “I reported data from tests of adult, black-legged ticks collected at 12 sites in VT since 2013.  We have some date from collections dating to 2011, but in 2013 we got a new grant, began working with new collaborators, using different DNA protocols, and I do not lump the data from the two different projects into a single analysis.”

Q: Do adult and nymphs have the same prevalence of bacteria?

Alan Giese: “Borrelia prevalence is lower in nymphs than in adults (nymphs have only fed once whereas adults have fed twice, so adults have had twice as many opportunities to acquire the pathogen).”

Q: Adults are more likely to carry the Lyme vector, but nymphs are more likely to transmit it to humans. Why?

For this we turn to Dr. Anne Hoen, Assistant Professor of Epidemiology and of Biomedical Data Science at the Geisel School of Medicine at Dartmouth:

“From a public health point of view, it is the nymphal ticks that are considered to represent the greatest threat to humans as a Lyme disease vector. It is thought that this is because the nymphs are small and likely to go unnoticed and are active in the spring and summer months when people tend to spend time outdoors. When we talk about risk for exposure to the Lyme disease agent, therefore, we usually talk about the density of infected nymphal blacklegged ticks. I know this sounds like a minor detail but the nuance around the tick stages, their likelihood of being infected, and their seasonal activity patterns is really relevant to Lyme disease epidemiology and, I think, is important information for the public to have.”

Q: Can males and females both transmit Lyme disease to humans? I’ve heard I only have to worry about females.

Anne Hoen: “Both males and females can transmit Lyme disease to humans. The male and female blacklegged tick nymphs, as far as I know, are equally good at transmitting Lyme disease. They look and behave the same so we don’t even distinguish between them. As adults, males don’t attach for long, if at all, to their host. The female has to attach and take a full blood meal in order to lay her eggs. But the male is only on the host to find the female—they mate on the host. So unlike the female, the male has no job to do after mating and doesn’t need a full blood meal. Because the males don’t take a real blood meal as adults, they aren’t effective at transmitting Lyme disease to humans. So really the answer is yes, both can transmit it, but in practice, if you find a male adult tick on you, it’s probably not going to be attached long enough to transmit anything to you and is not really a threat. The nymphal males and females are impossible to distinguish with the naked eye and both are effective Lyme disease vectors.”

Clarification 2:24 p.m. 6/8/15 The headline has also been clarified.

Clarification 1:30 p.m. 6/8/15 This post has been updated to clarify that black-legged ticks, also known as deer ticks, are the particular species of tick that carry Lyme.