In the second episode of our series on vector-borne diseases, Anya talks with Dr. Christine Petersen about tick surveillance and tick-borne diseases.

Anya Morozov: 

Hello everyone. And welcome back to From the Front Row, brought to you by the University of Iowa college of public health. My name is Anya Morozov. And if this is your first time with us, welcome. We’re a student run podcast that talks about major issues in public health and how they are relevant to anyone both in and outside the field of public health. Last week, we spoke with Dr. Ryan Smith about mosquito and a little bit of tick surveillance across the state of Iowa. Today, we are continuing that conversation by speaking with Dr. Christine Petersen, a professor in the Department of Epidemiology here at the University of Iowa. Her work focuses on the prevention of zoonotic diseases, including tickborne diseases, which are the topic of today’s episode. Welcome to the show, Christine. 

Christine Petersen: 

Thanks so much, I really appreciate it. 

Anya Morozov: 

So to start off, can you talk a little bit about your career path? We asked a similar question to Ryan last week, but what got you to study of all things ticks? 

Christine Petersen: 

Yeah, well I was one of those kids who was like pulling feral cats out of bushes and catching frogs and snails and all those crazy things. And so my path to becoming a veterinarian was pretty straightforward. But then when I was a vet student, I got a cool grant called expanding horizons that allowed me to spend the summer in Kenya. And it was there that I got to know a lot more about both the interface of animals with people and the diseases that they can share. And a lot of those are vector born because that’s a quick way for a disease to jump from one population to another. 

Christine Petersen: 

And then ticks in particular, I’ve been studying a cohort of hunting dogs for other diseases they have. But in talking to their people, their owners or caretakers, often it’s tickborne diseases that were causing a lot more trouble, and in a lot of instances, in places like Brazil, actually killing the dogs. And that of course is a major comorbidity as a epidemiologist. So we started looking at it just to be able to really know how much of what we were seeing was because of the disease of interest and how much of it was also associated with these tickborne diseases. But as particularly Lyme disease is the number one vector borne disease in the United States, we quickly started just looking at the tickborne diseases themselves for our own interest. 

Anya Morozov: 

Yeah. So your work kind of spans globally then? 

Christine Petersen: 

Absolutely. 

Anya Morozov: 

So I guess just focusing specifically on Iowa, can you give us a brief introduction to the types of ticks and the diseases that they can transmit here in Iowa? 

Christine Petersen: 

Yeah, so probably the first one that people talk about across the country is the black legged tick, or some people call it a deer tick, which is scientifically known as ixodes scapularis. And that is the tick that’s known to carry Lyme disease in the Midwest and the Northeast of the United States. And it also has a couple other diseases that can kind of hitch a ride as well. One is called Anaplasma. There’s two different species of Anaplasma. One is phagocytophilum, and the second one is platys. And those two names come from the different blood cells that it’s going to get into. So phagocytophilum, means it’s going to go into those phagocytic cells and platys is platelets. And then the third disease that can also be carried in those blacklegged ticks is Babesia, specifically for people, Babesia microti. And it’s a single cell protozoal disease. Microti doesn’t cause as much disease in animals, but there’s other Babesia species that do. And actually that was the topic of one of my recent epi PhD students. 

Anya Morozov: 

So how do you monitor the different types of ticks, and I guess the populations of ticks, across the state or in your research, and the rates of tickborne diseases as well? 

Christine Petersen: 

So to look at ticks, there’s a bunch of different ways to do it. Kind of the traditional ways are dragging or flagging for ticks. And that’s where you carry a white cloth, we like to use flannel because it’s kind of more sticky and the ticks can cling onto it better. And you literally walk through an area that you think you might find ticks. And you stop in a regimented way every so often, usually a certain distance or a certain amount of paces or time, and then you look at that cloth very carefully because of course the nymphs and the larva of these ticks are very tiny, and you pick them off. And usually you do that with some nice forceps and you stick them into a tube because you might have some idea of what tick it is just from looking at it on that cloth, but sometimes you’re getting, especially those particularly little ones, you need to look under a microscope to be a hundred percent sure which it is. 

Christine Petersen: 

There’s some other ways. So there’s trapping methods that use sticky tape and carbon dioxide to pull in the ticks, because they think it’s a blood meal because carbon dioxide of course is what mammals breathe out, so they’re drawn to that. And then they get caught on the sticky tape when they go crawling across. And then more recently, citizen science efforts using applications like on your smartphone have really grown in both use and popularity. So there’s the Center of Excellence in Vector Borne Diseases that’s headquartered in Madison, Wisconsin at the University of Wisconsin, and they’ve developed a tick app where you can use it to identify the tick you found on a walk, on yourself, on your pet, and then enter in where you found it. 

Christine Petersen: 

What’s funny is they’re actually looking for where in geography, but often people will also tell like where on their body, which of course gets really interesting sometimes and maybe a little [inaudible 00:06:07]. But then they use that database to map it over the expanse of the Midwest to then follow where we’re seeing different species. And then in terms of the diseases, you can both test those ticks that are on drag, so they’re called questing ticks. They’re the ones looking for a blood meal so they shouldn’t have any pathogens in them from a recent blood meal. Instead if they have detectable spirochaetes like borrelia in them, it means that came basically through another life stage and they’re persistently infected from larva on. 

Christine Petersen: 

If we want to use Sentinel species, then that’s one of the things my lab does. We use a large cohort of those hunting dogs who spend a lot of time out in the habitat where these tickborne diseases are found. And that means that they’re at very high risk. And they can kind of be used as cotton swabs running through the woods to pick up the ticks that are out there, but also the diseases that are out there. And that helps us understand what we as humans that are often going into those spaces with our dogs would also be at risk of acquiring. 

Anya Morozov: 

Can you actually talk a little bit more about your work with hunting dogs? Because I did a little bit of reading into it, but I didn’t realize, like you mentioned, you’re doing it in Brazil as well. I didn’t know it was global. I thought it was just kind of like the Northeast United States. So can you talk a little bit more about that work? 

Christine Petersen: 

Yeah. So in Brazil, we’re actually studying a different vector born disease, primarily one that’s a protozoan disease called leishmania infantum, and that’s a disease that is zoonotic as well and vector borne as well. But it’s not carried by ticks, it’s carried by a little sand fly. But dogs are the reservoir for it, and also kind of serve as that Sentinel host. So it’s a disease that kills between 20,000 and 40,000 people every year. And because of that, and because of the role that dogs play in kind of keeping those diseases in peridomestic areas where people are at risk as well, especially kids, that’s why it’s called infantum. There’s ways that we can use surveillance of and intervention with dogs to help prevent disease in those populations then, whether it’s in kids or in immunocompromised populations. And that’s what we see in Europe. 

Christine Petersen: 

So in Brazil, as I was saying, we were out in these neighborhoods talking about using insecticide impregnated collars, or other vector treatment to help prevent these diseases. But one of the great impacts that we were having at the same time was preventing tickborne disease. And a lot of the dog owners were really worried about tick disease. Tick fever they called it. And that specifically was ehrlichia canis. And it caused a really profound anemia and the dogs can die of that anemia. So having learned that, and knowing that about 80% of the dogs in the area that we were working in Northeast Brazil called [inaudible 00:09:15] Brazil, we then did a longitudinal study. After doing that cross sectional study in Brazil, we did the longitudinal study here in the United States and found that there really was a profound effect of these tickborne diseases, increasing their progression with the underlying leishmaniasis or leishmaniasi infection, and that by preventing the tick disease, we can actually prevent the protozoal disease, which is much harder to treat. 

Anya Morozov: 

And I guess as someone who, like I was once pre-medicine and then I kind of meandered my way to public health, so I often find myself focusing only on how things like ticks or mosquitoes impact humans. But a lot of your work also centers around animals. So why do you think it’s important to focus on humans and animals and the environment when studying something like vector borne disease? 

Christine Petersen: 

Well, you’re obviously not alone in that focus. And that’s the way a lot of medicine has gone, particularly after the epidemiologic shift that happened in the sixties when people were declaring infectious diseases, basically eradicated, and we didn’t need to think about them anymore. So then we really were just trying to treat people with the stuff that they came in with. But especially when you talk about vector-borne diseases, vectors don’t really care, they care a little bit, but not too much what they get their blood meal from. So they’re likely to take blood meals from multiple different species. And especially if they feed on one thing and then feed on another thing, that’s a great way to be able to transmit disease. The ability of a vector to live in a particular area is really based on things like temperature, humidity, wind speed, what your winters are like, so that helps dictate whether there’s seasonality or not. 

Christine Petersen: 

And all of that put together really is what sets up a particular area for being very rich and rife with these different vector borne diseases. Or that they have different patterns, so if you know that the disease is also infecting another animal, usually another mammal, but certainly the vectors are animals too, both the arachnids and the insects. Those are different parts of the life cycle that also can be a great way to do interventions. So you can have different abatement methods to get rid of where they breed. You can use different insecticides to protect those domestic animals that I was just talking about, those sentinels that can also be reservoirs. And that can make a huge difference in the human exposure in a lot of these places. So for instance, one of my collaborators, who is a really smart and sharp woman, also a veterinarian that trained in Portugal, she came up with the idea that we could use the reservoir for Lyme disease, which is the white footed mouse, as kind of a little antibody factory. 

Christine Petersen: 

So if we feed them pellets that are coated with an outer surface protein of burrelia, they’ll make antibodies against it. Then when the tick feeds on them, which they do a lot, they will take up those antibodies from the mouse and it will get the burrelia out of the ticks. So basically, you can eliminate the disease from the landscape without having to try to convince people to get vaccinated or to wear potentially toxic insecticides. So it’s a way that we can make a big difference in exposure to the infectious disease without having kind of untoward other toxic exposures through some of these little things. 

Anya Morozov: 

Wow, that’s really interesting. I think it’s kind of getting at like a lot of the public health work, I feel like goes behind the scenes and. I think there’s more of a push now to make public health more visible, but in the past, people have said like when public health is doing its job, you don’t even know it’s there. And that’s a great example of how that happens. I guess, do you know anything about how rates of tickborne diseases have changed over the years, or maybe like the range of different tick species? And what do you think influences these rates from year to year? 

Christine Petersen: 

Well, we know that pretty much across the board, all tickborne diseases are increasing significantly in the United States, whether it’s Lyme disease, Anaplasma ehrlichia, Babesia, all the ones that I was just talking to you about, all of them are on the rise. Some of that’s for good reasons, that Americans are trying to get out and be healthy and get those steps in. But they’re taking those steps in places where there’s sticks and increasing exposure. But some of it’s because of the things we are doing to our environment. So we’ve really changed the environment and we’ve made it so that we don’t have a lot of predator species, which have led to large overpopulations of creatures. Like white tailed deer. People think that white tailed deer are the reservoir for Lyme disease, and that’s not exactly right. They really are only fed on by those adult ticks. 

Christine Petersen: 

So they’re not kind of letting the whole life cycle happen on them or in them. And that’s the role of the mouse and other rodents. But what they do is they move ticks across landscapes. So for instance, there was not a lot of Lyme disease in Iowa, but it’s really growing in the Northeast. And we really think that’s happening because the Northeast is a beautiful area that’s got like the whole driftless landscape and lots of cool state parks, but that means it’s a great place for deer to swim across the river and go hang out. And then those deer move into our agricultural areas where they do quite well, because there’s corn and other things to eat off the ground. And that’s how it’s slowly moving from kind of Northeast to south across the country. It’s also true that there’s a different tick species, the lone star tick, or amblyomma americanum, that’s particularly in Arkansas, Missouri, and that’s slowly creeping its way northward. So we’re kind of the magic [inaudible 00:15:30] ground where we’re going to have all the fun ticks that are vectoring various diseases in Iowa. 

Anya Morozov: 

That’s interesting. When we spoke to Dr. Smith last week, he also said that we’re kind of at this intersection or edge of the range of certain mosquito species as well. So it’s a fun place to be, in Iowa, I guess. 

Christine Petersen: 

Yeah, exactly. Woohoo, yay. 

Anya Morozov: 

For the lone star tick, do you know if the shift in range is also due to the white tailed deer traveling or is that something else? 

Christine Petersen: 

Yeah, they can be found on deer, but they aren’t as prone to deer. They cause a disease called tularemia, which is also known as rabbit fever. So they really like rabbits, they like other rodents. But they’re pretty aggressive species and they’ll pretty much feed on whatever they can, which means that they tend to get rides on what’s abundant and around, which is a lot of rodents. 

Anya Morozov: 

Okay. And then I guess kind of talking about, I know I’ve done some summer hiking myself and want to stay safe from ticks, not a fan of them. So what can individuals and communities do to reduce their own risk or even their pets risk of getting tick borne diseases? 

Christine Petersen: 

Well, so the pets are almost easier at this point because there are multiple pretty useful tick products out there. There’s a newer class of them called [inaudible 00:17:00], which of course does not roll off everybody’s tongue, but there’s three or four of them, and your veterinarian will know what they are, and they work really well. So I highly suggest if you have a furry friend that you like to take out into those areas, please get them on good tick control, and preferably year round because ticks come out anytime you get a day above 50 degrees. And pretty much every month, except for maybe February, usually has at least a day or two where that happens these days. In terms of for us, the one option is just, don’t go into tick habitat. But I, like you, like to go hiking and go out into the woods and do fun things. So then your options are use good insecticide, like deet or certain citronella compounds can work. And particularly use them kind of down on your socks because ticks start from the ground. 

Christine Petersen: 

I’ve heard these myths that like ticks fall from the sky, like from trees or something. And it’s because people find them in their hair, so they assume came that way. But no, they’ve crawled up your whole body. And that’s where they’ve decided to get the blood meal. Not to freak people out, but that’s what’s happening. So that’s where really dorky but useful things can be tucking your socks into your pants or at least wear pants versus shorts if you can convince yourselves to do it. The other thing that’s useful is to try to use lighter colors because as those ticks, which tend to be darker colors are crawling up your body, when you come out of the woods and you are hiking with a friend, that friend can do a quick tick check of you and see if they see a tick on you and then vice versa. And it’s much easier to see if you’re not wearing black, brown, or gray. 

Anya Morozov: 

Wow, that is not something that I would’ve thought of, but that’s a good tip. For my next question, I know we’ve kind of only scratched the surface of the work you do. When I hear about your work around the college, it seems like you’re everywhere all the time. So this can be specifically focused on your work around ticks or more broadly, but the 10 essential services of public health center health equity, so I’m curious to know like what role does health equity play in your work? 

Christine Petersen: 

Yeah, well we haven’t used it as an official outcome or metric, but of course it has a huge role. And some of the things are simple. So when we talk about neglected tropical diseases, the people who get them are the people who are poorly nourished, usually have other severe comorbidities. For instance, the work I do in India on that protozoal disease, leishmaniasis, are often Muslim communities, which unfortunately, in the news we were hearing about again, Muslim Hindu strife in India. And in Brazil, it’s kind of neighborhoods on the outside of the city, favela like places where we see the most exposure to leishmaniasis. And then when you talk about health disparities and health equity in the United States, it’s a little interesting with tickborne diseases because both rich people and those without as much money like to go outside and do fun things. It’s kind of why they’re outside that’s very different. 

Christine Petersen: 

So there’s been outbreaks of various problems in landscapers or people doing yard work. And so the exposures might not be that different, but what’s really different is then access to care, ability to get a good diagnosis because if you’re going to an emergency room and paying out of pocket, one, you’re probably likely to wait a long time and with Lyme disease, that makes a huge difference. If you get on antibiotics sooner, you’re going to have much better outcomes than if you kind of get this rash, but you’re like, “Okay, well it doesn’t hurt, I’m fine.” And then you move on to the other problems, Lyme arthritis or carditis or neuropathies. And that of course has much greater impact on your health, on your ability to work, and makes a huger, yeah, good word, makes a bigger difference in [inaudible 00:21:05] outcomes. So it’s pretty straightforward to know that there’s not equity when it comes to those diseases. 

Anya Morozov: 

Yeah. So I think even in the United States, just making sure there are protections in place for people who have to work around ticks to get them care quickly would be a good, bigger step. 

Christine Petersen: 

Yeah, fantastic. And because for these diseases we don’t have great preventative measures, I mean yeah, tucking in your socks and wearing light colors. And usually that’s things that most landscapers are already doing, but you still have to do the tick checks. And when you’re working two different jobs and you have to run between them with a quick shower, you may not do the good tick check and you miss it. 

Anya Morozov: 

So now we’ll move on to the last question that we ask to everyone who comes on the podcast. What is one thing you thought you knew but were later wrong about? 

Christine Petersen: 

Yeah. Well, I’ve definitely been wrong about a bunch of things over the years. I think, like a lot of people, I didn’t really understand the role of deer in Lyme disease. And it took me kind of talking to different mammalogists actually to understand more of the role of the rodents versus the deer and how they both have a role, but they are certainly different. And how interventions in deer can be useful to stop expansion, but not so much decrease incidents in a particular area. So that was something I had to learn. And I think it’s because of the misnomer of the tick being the deer tick. I was like, “Well, you just get rid of the deer tick and get them off a deer and then we’re fine.” Yeah. I can give you multiple examples if you want. That’s one. 

Anya Morozov: 

Yeah. I think most of us, myself included, have more things we thought we knew, but were later wrong about than things we turned out to be right about sometimes. Okay, well this has been a great conversation. It’s been great to learn about your work. And thank you so much for coming on the show today. 

Christine Petersen: 

You’re very welcome. It’s been a real pleasure to talk about it. And yeah, just remind everybody to do tick checks and get your pets on preventatives. 

Anya Morozov: 

That’s it for our episode this week. Big thanks to Dr. Christine Peterson for joining us today. This episode was hosted, written, edited, and produced by me, Anya Morozov. And you can learn more about the University of Iowa college of public health on Facebook. As always our podcast is available on Spotify, Apple podcasts, and SoundCloud. If you enjoyed this episode and would like to help support the podcast, please share it with your colleagues, friends, or anyone interested in public health. Do you have a suggestion for our team, a comment about the show, or a question that you like answered? You can reach us at cph-gradambassador@uiowa.edu. This episode was brought to you by the University of Iowa college of public health. Until next week, stay healthy, stay curious, and take care.