June 6, 2022 edition of A Way to Garden public-radio show and podcast with Margaret Roach.
How are we doing in the effort to reduce tick encounters and the diseases that ticks carry and transmit to humans? The results from a multi-year study in Dutchess County, N.Y., one of the areas of the United States with the highest rates of Lyme disease, shed some light on that question.
I talked to longtime tick researcher Dr. Felicia Keesing about the findings, and to get her expert advice for best practices that each of us gardeners can take for personal protection. She is a Professor of Biology at Bard College in Annandale-on-Hudson, N.Y., and one of the two directors of The Tick Project, with Dr. Rick Ostfeld of Cary Institute of Ecosystem Studies in Millbrook, New York.
Though there is still no silver bullet yet, there are tactics we can each follow to reduce our risk. There is also research under way on a potential new approach to a vaccine that she told me about.
Margaret Roach: Welcome. I feel like before we get started, I always like to know how people got into what they do, and I just want to ask you: How did you, why did you, when did you get involved with ticks? Are there other animals or arthropods that have been your main focus, or how did this happen for you?
Felicia Keesing: That’s a great question and it will be a revealing answer, I think. I actually did my PhD on large mammals in African savannah. I worked in Kenya studying how the absence of elephants and giraffes and buffalos and things effect savannah communities. It was a sort of conservation-related project, and so it might seem a very big jump from there to ticks, but actually in that same period of time I met another scientist named Rick Ostfeld, the same Rick Ostfeld you just mentioned, and he worked on ticks.
So, at the same time we were actually getting married, I started working on ticks, too. I like to say that I married into ticks.
And it turned out that there were a lot of ticks in Kenyan savannahs, too. So my work there moved into some of the same sort of disease-oriented directions as I was beginning work here in the Northeast on tick-related questions.
Margaret: So, marrying into ticks, is that tick humor? That’s tick humor?
Felicia: [Laughter.] I’m not sure anyone else can say that, actually.
Margaret: Right. Let’s quickly first just sort of set the stage, and explain the extent of the tick problem. I know there are many species in different regions, but your work focused on the black-legged tick, which I think is prevalent in the eastern half of the United States and into maybe into southern Canada. Is that correct?
Felicia: Yeah, that’s correct. I would say our work focused on the black-legged tick because that’s the most common tick around here, but actually we were focused on ticks more broadly, and there are other ticks here in the Hudson Valley, where Dutchess County is. There are other ticks, and so we were focused on ticks broadly, but the vast majority of those here, even now, are black-legged ticks.
In other parts of the country there are lots of other kinds of ticks, and new ones appearing at different places and different times.
Margaret: Yes, I think that one of the things that you reported, or at least in a presentation that I watched about the report, the study results, is that there’s been such a massive increase in the range of black-legged ticks in the last 20 years, or even less than 20 years, a massive amount of increase in their population spread.
Felicia: Yeah, one of the things that’s interesting is that the best documentation that we have of that country-wide is really the increased number of cases of tick-borne diseases. That’s what we actively track. We have data from particular places like at our study sites in Dutchess County, where we have a longterm record of what’s happened to tick numbers through time in one place.
But interestingly, the federal government doesn’t actively track where ticks are. There isn’t an active surveillance program for ticks, so we don’t have as much information as we might ideally hope for. That’s not to say they aren’t collecting data, but there isn’t an active surveillance program. So, most of our information comes from tracking cases, or from looking at numbers in particular locations, but we do know that there are ticks arriving in places that they weren’t found or weren’t abundant in the past. Following that, not surprisingly, we see big increases in cases of Lyme and other tick-borne diseases in areas that previously didn’t experience them.
What comes to mind for me thinking about the Northeast, for example, is that Vermont, New Hampshire, and Maine 20, 25 years ago would not have talked about tick problems, I think, and not at all the same way that they do now-
Felicia: …about ticks and corresponding diseases. And in a different direction, western New York has now a very significant tick problem, where they didn’t have such a Lyme disease problem anyway, even a decade ago. So, it’s happened very rapidly and spread in lots of different directions.
Margaret: Right, and we have multiple diseases and we have, I think you say in the report, an estimated $1 billion dollars in medical costs in the country from Lyme, and maybe approaching 500,000 cases a year that we know about, or some numbers like that. So, not a small thing and as you point out, there’s not a vaccine. There’s no real prevention thing medically, no silver bullet.
Diagnosis is not necessarily … Not everybody who gets bitten and may even get infected with one of these diseases, gets diagnosed. It’s complicated, so you and scientists such as yourself, want to find other avenues for our protection. And I guess spraying whole yards or larger areas with the chemicals that would kill ticks would also be very hazardous to critically important other animals, other insects and arthropods. So, it’s not really a plan. What did you do? What did you explore instead?
Felicia: We are one team among many that’s interested in trying to prevent pieces of tick-borne disease, and one of the most obvious ways that we’ve all thought we could do that was to reduce the number of ticks. So, if you reduce the number of ticks, in principle, you would think that should lead to a reduction in people’s encounters with tick, and that should lead to a reduction in the number of cases of tick-borne disease. That’s sort of how the reasoning goes.
There had been a study back in 2016, a large-scale, extremely well-done study where they tried spraying a chemical called Bifenthrin. This is one of those chemicals like what you’re describing that has what we say are non-target effects. It can affect beneficial animals as well as ticks.
And so, they sprayed this on people’s yards and they didn’t see a difference in the number of cases, even though they saw a substantial reduction in the number of ticks in people’s yards.
So we designed our study informed by that, with a couple of significant differences. One is that we were not willing to use a chemical that had so many non-target effects. We chose two products that were commercially available, but that were known to be safe for the environment, for people, and for pets.
Those two products are a fungal spray called Met52. This fungal spray is derived from a fungus that naturally occurs in forest soils in many parts of the world. That fungus has been developed in the laboratory to have strains that are specific to ticks, and so the spores infect ticks and kill them. That’s the way it’s supposed to work, but without having effects on other creatures. This spray, Met52 spray, gets sprayed with a high-pressure sprayer around your yard and the idea is that the spores then infect ticks, and kill the ticks before they have a chance to get on you or your pets. That was the first product.
The second product is called The Tick Control System, or TCS. People sometimes call it a bait box. It’s basically a little box about the size of sort of a sandwich box, maybe a little bigger than that. And it has a hole in it with a little bit of bait that draws in small mammals. The idea is that mice or chipmunks would be drawn into this box, and while they’re in there nibbling on this little bit of bait, they get dabbed with a chemical called Fipronil, which is a tick-killing chemical It’s the product, the active ingredient in Frontline, which a lot of people put on their pets.
Felicia: The idea is to target this chemical directly on the hosts that are most responsible for infecting ticks. [White-footed mouse photo from The Tick Project.]
Margaret: And that’s a really important point. I don’t want to interrupt, but just to say we have the common name for the black-legged tick of “deer” tick, but dot dot dot. My obsession for many years [laughter], knowing a little bit about ticks, is mice. I am anti-mouse over here because they are where… Ticks aren’t born with disease; they aren’t born with diseases, but when they take that blood meal often from a white-footed mouse, a rodent, they can get infected if that animal has it, yes? I’m not a scientist, but that’s my basic understanding.
Felicia: You may not be a scientist, but you’re doing a wonderful job of explaining it.
Margaret: [Laughter.] O.K., so that’s-
Felicia: That’s exactly right, yeah. Ticks feed on lots and lots of different hosts, as we call them. Those hosts are often mammals, and we are one of many possible mammals that they might feed on, but they also feed on birds and reptiles and things. When baby ticks hatch out of their eggs, as you say, they’re not infected with most of the pathogens. For example, they’re not infected with the bacterium that causes Lyme disease. They have to become infected by acquiring that bacterium from the host that they’re feeding on. The host that they become infected on from most readily is the white-footed mouse here in the East.
So in fact, 90 percent of uninfected ticks that feed on a mouse will become infected, whereas basically no ticks that feed on deer become infected. It’s a misnomer in multiple ways to call it a deer tick.
Margaret: Yes, O.K., good. You wanted to really take, I believe you call it, a “neighborhood approach.” Is that correct? You scaled this, you did whole neighborhoods with these two products and then some neighborhoods that were the controls that didn’t have the products, but were a part of the study and was a multiyear study.
Felicia: That’s exactly right.
Margaret: O.K. How long did it go on and what did you find?
Felicia: Yeah, we had five years of active treatments—five years of active surveillance, I should say. We treated the properties for four years, and as you say, we were treating the whole neighborhood. So we recruited participants from 24 neighborhoods in Dutchess County. Each neighborhood consisted of a cluster of about 100 homes and we recruited as many households from each of those neighborhoods as we could.
In a given neighborhood, we might have 40 percent of the houses of the households participating and all 40 of those households received the same treatment. As you say, we had control neighborhoods. Neighborhoods either got active fungal spray, or active bait boxes, or both, or neither.
Felicia: So we were able to compare the results, and we really used the sort of gold standard of like a clinical trial to figure this out. We had replicates—we had six of each type of neighborhood. So there were thousands of people involved in this study, about 3,000 people and about 1,000 pets enrolled in the study for those years. We treated them, as I say, with these products over a number of years. And one important point is that neither the participants nor any of the people collecting data from those properties knew which treatments were being applied to which neighborhoods, so we had placebo controls.
Felicia: That’s so that people who, for example, knew they were getting both active treatments or knew that they were getting neither didn’t behave differently. So no one knew: We had bait boxes at every house enrolled in the study, but some of the bait boxes had active treatment—some had active chemical in it and some of them had nothing, no chemical at all, but you couldn’t tell the difference.
So we were very careful about that kind of thing, and at the end when we looked at all of the numbers, what we found is that the bait boxes, these little boxes that have bait and draw in rodents and put Fipronil on them, that those reduced the number of ticks in the yards over all by about half. They dramatically cut the number of ticks in people’s yards.
They also reduced the number of cases that people reported in their pets. But we didn’t see a reduction in any of the data that we collected on people. We had people report to us whenever they encountered a tick, and we prompted them every two weeks to report that information to us, if anyone in their household had encountered a tick in the previous two weeks. We didn’t see a difference in that, based on our treatments, and we didn’t see any difference in disease either from the reports of diagnosis that the participants gave us themselves, or from the followup that we did with physicians when participants gave us permission, where we followed up on those cases and got information from the physicians directly.
We saw, out of well over 100 cases of Lyme in these neighborhoods in people, we didn’t see any difference based on whether their yards had had reduced numbers of ticks or not.
Margaret: Right. Right. There’s future work, future things to think about that you’re probably going to explore, and we can talk about that. But when I read those results and I had read some of the preliminary ones awhile back, it made me say, hey, this study, which is so well-structured and so forth, is a reminder of the importance of personal protection and each of our individual vigilance.
That there’s not, again, a silver bullet, a magic bullet, to “fix this.” We still have to be vigilant.
Because I know a lot of people have said, “Oh, I got the bait boxes,” because some of these, as you said, are commercial products and they are just like set it and forget it. They’re like, “I got that. Now I’m protected,” and they’re not doing the vigilance, and that makes me very nervous.
Felicia: Yeah, it makes us really nervous, too. We hear this, too. We’ve been very up front that we didn’t see an effect on people and that was the point, to see if there was an effect on people. Because honestly, to this point in all these years of research on prevention strategies, we collectively, the tick research community, has never found an intervention that actually reduces cases in people.
Felicia: We’ve got various things that reduce tick numbers on localized levels, but we’ve never seen that followed through to cases. In the last few years, what we’ve had is two studies that have followed that through to cases, and both of them show reductions in tick numbers, but neither of them sees an effect on human cases.
So as you say, it’s really important that we recognize a bunch of things. One is that we still don’t have a way to protect ourselves from tick bites where we can just set it and forget it or spray it if people are willing to put those kinds of chemicals on their lawn and elsewhere.
There are known, effective strategies for personal protection, but people are challenged to take that kind of responsibility and be really careful. I’m not saying that they’re all easy, either. They’re tedious.
So, among those, and you may use some of these, Margaret, when you’re outside in a tick habitat at a time when ticks are active—which around here is getting to be more and more of the year—when you come in, one of the things you’re supposed to do is take off everything you were wearing, put it in a very hot dryer for 10 or 15 minutes, and then any ticks that are on that fabric should be killed. That’s been shown to be very effective at killing ticks. But not everyone has a dryer in their house, and that uses a lot of energy. It requires you to change and you might still have ticks on your skin, so you need to check for those, too.
So again, I’m not trying to trivialize the problem with personal protection. It remains a major issue, and this is why we were hoping that this study, or one of these other tick-reduction studies, would show an effect on people so that we could give people some other methods.
Margaret: Right, and so I think also recommended is a shower within two hours of outdoor activity, for instance, obviously thorough body checks, and another self-check I think before bed is not a bad idea in case you missed it the first time-
Felicia: I absolutely agree with you about all those things.
Felicia: And I would still say you still have to be really careful. You should still be, in the days following, be checking to see if you have unusual swellings or red marks or something like that because the ticks don’t just wash off when you’re in the shower. This is particularly important in what we call the nymphal tick season, the time when the sort of mid-life-stage ticks are around. That’s now and into June and even into July, because those ticks are so tiny that they’re really easy to miss, and they’re unlikely to get washed off from you just rinsing in a shower, especially if they’ve begun to embed their mouth parts at all.
Felicia: So you really need to keep an eye on, be kind of doing tick checks for a while.
Margaret: Now, as a researcher out in the field, you cannot use some of the other tactical gear, so to speak, like you can’t use repellent or a treated garment. You can’t wear a treated garment, I don’t suppose, when you’re researching [laughter].
Felicia: That’s exactly right.
Margaret: So those are other options that some people are using, correct? They’re either sending clothing to have it treated or they’re buying specially treated clothing. I think it has Permethrin, is that correct, on it-
Felicia: Yeah. Yep.
Margaret: …usually, and that lasts for a certain number of washings and so forth. But you can’t really avail yourself of that in your work.
Felicia: We can’t because we’re trying to make accurate counts of tick numbers so we have several methods that we use. One is we, obviously, train our staff in how to do very, very thorough tick checks, but our staff also wears specialized clothing. It’s not Permethrin-treated, but it is a sort of what we’ve been described as looking like Ghostbusters.
Felicia: And kind of one-piece, kind of long-sleeved painting suit that’s white. Ticks show up well against that white background, so it becomes easy to see them if you’re looking very closely and carefully. Then we also wear light-colored socks, preferably white, and tuck our pant legs into them, because when ticks get on you they’ll tend to walk up, and so that keeps them on the surface of the clothing rather than get up inside your pant leg. That kind of protecting your wrists, where a tick might come up your sleeve, and protecting your ankles is a good idea. Again, long-sleeved shirts and long-legged pants are a good option as opposed to shorts and a tank top or something when you’re in tick habitats.
Margaret: And pet checks. Oh boy, pet checks, huh?
Felicia: Yeah, so pet checks: We don’t have pets ourselves-
Margaret: Neither do I, but I have friends who do. Boy, that’s where they get a lot of them in the house.
Felicia: Yeah, and there are some effective tick treatment methods for pets that aren’t available to people, too, so that’s worth thinking about.
I will say there is a promising future direction that [laughter]… Talking about ticks can be a little bit doom and gloom, so I do want to point out that there is some promising news in the prevention realm. It’s not without its challenges, as you’ll see in a moment, but that is that there have been some groups trying to develop tick vaccines.
Felicia: And so the idea is what if you could get a vaccine that essentially made you aware if you were being bitten by a tick, because most people never notice the tick that bites them. So, that’s why it’s so hard to find them. With a mosquito you often feel it, but with a tick you don’t. So you often, most people who get Lyme disease, never notice that they had a tick on them. And that’s because ticks, when they embed their mouth parts in your skin, they also inject a bunch of chemicals that prevent your immune system from detecting them.
Felicia: So you don’t even know they’re in there. It’s really quite a remarkable kind of pharmacological cocktail that they put into you so that you don’t know that they’re taking this blood from you. But these tick vaccines cause your immune system to be able to detect that a tick is doing that to you so that your skin reacts like it would to a mosquito bite, for example, and you can remove the tick before it does serious damage and potentially injects a pathogen into you.
There was a big paper out about six months ago that showed that a tick vaccine was effective in guinea pigs, and what happened is the guinea pigs developed these very pronounced red kind of welts, like a mosquito bite, at the site of the tick injecting its mouth part. That’s promising, because there are some people who have that reaction to ticks and that’s what gave people the thought that this might be an approach that could work.
In fact, I have that response when a tick embeds its mouth parts. My immune system reacts very strongly to that, and I will know that a tick is biting me. It’ll wake me up in the middle of the night. It’s an incredible asset in my line of work, to have that, and use it.
I still do tick checks and all those things, but I have a sort of second line of defense that if a tick does bite me, I can usually tell that it’s there before it’s likely to do any damage.
So, these tick vaccines are promising on the horizon as something that people could use that would not prevent the tick from biting them, but alert them when one is.
Margaret: So we said the black-legged is not a deer tick per se, however deer can carry around a lot of ticks on them if they’re moving through your garden or your world. Is a deer fence a thing that could potentially also minimize the number of ticks that come into your … because a mouse I would imagine, has several ticks on it as opposed to a hundred or more, maybe. I don’t know how many are on a deer, but do you know what I mean? [Wikimedia Commons photo, above.]
Felicia: Yeah. Yeah, I do. The role of the deer is not just to move the ticks around, potentially, but also that they are often the host for adult ticks, which lead to the laying of the baby ticks the next year. Actually, mice can have dozens and dozens of ticks on them.
Margaret: Oh. O.K.
Felicia: So they carry quite a few. We did a meta-analysis of a bunch of studies a few years ago. This was led by my colleague Ilya Fischoff, and deer fences did show a modest reduction in tick abundance in people’s yards, but it was, as I recall, fairly modest.
Felicia: And that’s in part because this deer effect is kind of complicated. There are other hosts that are probably most important.
Margaret: Well, Felicia, I’m fascinated. It’s a subject that I care a lot about and I’ve been fortunate to use my obsessive, crazy-self check regimens [laughter] and not get so far in all these years of gardening, get infected. But thank you for updating us and thank you for this work—it’s just so important, so I hope I’m going to speak to you again soon. Thank you.
Felicia: I hope so, too.