Ticks are a growing problem, no matter where you live

In the grand scheme of things, Lyme disease is a fairly new scientific discovery. It was first traced back to ticks in the late 70s and early 80s. The tick-borne illness can cause a rash, fever, pain, neurological complications, and even facial paralysis. It’s spread by only two of the nearly 50 species of ticks https://pubmed.ncbi.nlm.nih.gov/35973261/ in the United States. Historically, most Lyme cases https://www.cdc.gov/lyme/data-research/facts-stats/lyme-disease-case-map.html were limited to a small region, including the Great Lakes area and northeastern US. But thanks to changing temperatures, animal migration and shifts in land use, scientists say tick territory is expanding. So what does that mean for Lyme disease risk? And do you have to be worried about it in your own backyard? Interested in more episodes about pests and parasites? Email us your question at [email protected] mailto:[email protected]. Support public media with NPR+ and enjoy perks for over 25 podcasts like this one. It includes perks like bonus episodes, early access, archive access, curated playlists and sponsor-free listening. Learn more at plus.npr.org http://plus.npr.org. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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  You're listening to Short Wave from NPR. Hey, Short Wavers. Regina Barber here. And today I am joined by producer Hannah Chin. Hey, Hannah.

• 0:24Speaker 01

  Hey. So today I want to start our episode with a mystery.

• 0:29Speaker 00

  Ooh.

• 0:30Speaker 01

  It starts the way a lot of old mysteries start, with a group of kids in a tiny town in the middle of the woods.

• 0:36Speaker 00

  No, it's a horror movie.

• 0:38Speaker 02

  In the late 1970s, a small cluster of children came down with arthritic symptoms. And, you know, children aren't supposed to have arthritis. So this sort of alerted public health officials to something kind of funny going on.

• 0:52Speaker 00

  This is actually terrifying. Like, where did these kids live?

• 0:55Speaker 01

  All these kids lived in Connecticut, around a little place called Lyme. And as public health officials investigated, they started to trace it back to the woods. They were like, OK, there's some kind of illness. We don't know what it is. Maybe it's an insect, or a virus, or a bacteria, or something. But we know it's coming from the forest.

• 1:16Speaker 02

  So it wasn't until the early 1980s that the organism was identified as Borrelia burgdorferi, a spirochetal bacteria that was transmitted by ticks.

• 1:29Speaker 01

  This is Andrea Sway. She's a disease and vector ecologist at San Francisco State University. And she says this bacterium had probably been around for a while, maybe even millennia. This was just the first time that we noticed it and like had the tools to track it down.

• 1:42Speaker 02

  It probably increased in prevalence in that time due to a number of land use changes and sort of human settlement pattern changes that put people in higher contact with infected ticks.

• 1:54Speaker 01

  And nowadays, Connecticut is still a hotspot for Lyme disease. In fact, if you look at a map of Lyme cases, I actually looked at the CDC's just now, the vast majority of them, like more than 95%, are in the Great Lakes area and the northeastern US.

• 2:10Speaker 00

  So we're talking about like the upper right-hand corner of the United States?

• 2:13Speaker 01

  Yeah, exactly. And historically, that's what we think of as tick country, right? But Gina, scientists know that ticks are on the move. So tick country, and by association, Lyme country, is expanding.

• 2:28Regina Barber?

  So today on the show, we're doing a tick check, Short Wave style.

• 2:32Speaker 01

  We're taking a long, hard look at ticks, what we know about them, what helps them thrive, and how they acquire and spread Lyme disease.

• 2:40Regina Barber?

  Plus, why their territory is spreading, maybe even into your backyard. You're listening to Short Wave, the science podcast from NPR.

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• 4:18Regina Barber?

  Follow us to make sure you never miss a new episode. New ones drop every Monday, Tuesday, Wednesday, and Friday.

• 4:25Speaker 01

  OK, Gina, so we're going to start with like tick 101. Get ready to be a little bit grossed out.

• 4:30Regina Barber?

  I love school. Let's do it.

• 4:31Speaker 01

  To start, these arachnids have four stages of development. Egg, larva, nymph, and adult. After they hatch, they need to have blood meals at every single stage in order to survive.

• 4:42Regina Barber?

  Right, it's these blood meals that that's when they get infected with the disease?

• 4:47Speaker 01

  Exactly. And there's only two kinds of ticks that carry Lyme in the US. There's the black-legged tick, or deer tick, and the western black-legged tick.

• 4:55Regina Barber?

  OK, I don't know why that makes me feel a little better.

• 4:57Speaker 01

  And to be clear, these ticks aren't born with Lyme. They only get infected when they feed on an infected animal, like a bunny, or a bird, or a deer, or a human.

• 5:07Regina Barber?

  OK.

• 5:08Speaker 01

  And I asked Adela Oliva Chavez about this process. She's a medical entomologist at the University of Wisconsin-Madison.

• 5:14Speaker 05

  The bacteria will come with the blood that the ticks are taking. It will go to the mead gut, that is the stomach of the tick. And in the stomach of the tick, they will bind to the epithelial cells. So the lining of the mead gut of the tick, they will bind to that lining.

• 5:34Regina Barber?

  So this bacteria that causes Lyme disease, it goes straight to the tick stomach lining and it just like camps out there?

• 5:40Speaker 01

  Exactly. And again, ticks only feed once per developmental stage, right? So say the larva feeds on an infected host. That same larva will molt into a nymph. And then that nymph is now infected and looking to feed. And that's the first time that it can infect other hosts like us.

• 5:57Speaker 05

  When the tick then bites a human, the blood comes into inside of the tick. And the change in temperature inside of the tick, because the blood that is coming is around 37 degrees.

• 6:11Speaker 01

  And Adele is using Celsius here, so it's like 98.6 degrees Fahrenheit.

• 6:15Regina Barber?

  So that's the temperature of a human, right, when I'm healthy?

• 6:18Speaker 01

  Exactly. And this temperature trigger, right?

• 6:20Regina Barber?

  Okay.

• 6:21Speaker 01

  Your healthy human blood tells the bacteria in the tick that it's time to replicate. It's time to start moving from the stomach to the salivary glands of the tick. And that's when the transmission process begins.

• 6:32Regina Barber?

  So this is all happening during like the feeding process where the tick is like on us?

• 6:37Speaker 01

  Yes. And that's why the CDC gives this recommendation that you should try to find and remove ticks, if possible, within the first 24 hours.

• 6:44Speaker 05

  There is a lag time. It has to start taking the blood in. The bacteria has to replicate and then it's transmitted. So if you remove the tick in those 24 hours, you won't get sick.

• 6:58Speaker 01

  And that's how ticks transmit Lyme disease.

• 7:01Regina Barber?

  Okay, gotcha. But earlier you said that there are way more Lyme disease cases in like the Great Lakes and the Northeast area. So why is there such a difference geographically?

• 7:11Speaker 01

  Yeah, I wanted to know this too. So I talked to a disease ecologist. Her name is Jean Sau, and she specializes in tick-borne diseases at Michigan State. She told me there's a variety of different factors at play here, right? Temperature, humidity, habitat, and we're not going to get into all of them.

• 7:25Regina Barber?

  Yeah, that's a lot.

• 7:26Speaker 01

  But one big one is that Lyme seems to be more endemic in the north, maybe just because it's been circulating longer. So your probability of getting infected is higher.

• 7:36Speaker 06

  In the north, 40 to 60% of the adult ticks are infected with the Lyme bacterium, depending on where you are. But in the south, if you look at the adult ticks, it's very low, like 0.2%. And at a place where we collected a lot of these ticks.

• 7:52Regina Barber?

  Wow, okay. So it's like if you're rolling the dice, right? And there are fewer infected ticks, you might get bitten, but your odds of getting Lyme disease is pretty, is still pretty low.

• 8:02Speaker 01

  Yeah, it's really just a probability thing. And another factor is in the ticks themselves, right? The animals that they feed on and the way they get to them is different. In a number of studies that Jean and her colleagues worked on, they found that ticks in the north tend to feed on small mammals, so birds, rodents like squirrels and mice and chipmunks, as well as humans. And ticks in the south tend to look for hosts on the ground, below the layers of leaves on the forest floor. So sometimes birds, but more often reptiles, like lizards. Andrea Sway, who's the researcher that you heard at the beginning, says this is true of her California ticks as well. They seem to prefer lizards. And this is really important because it turns out some of these lizards have a superpower. They can clear the ticks' systems of Lyme disease.

• 8:44Regina Barber?

  That's so cool.

• 8:45Speaker 01

  Yeah, so back in the 1990s, a group of researchers looked at a key host for ticks on the West Coast, the western fence lizard. And they discovered that after feeding on this lizard, even previously infected ticks would become Lyme-free. Later studies found a specific protein in the lizard's blood that killed the Lyme disease bacteria, Borrelia burgdorferi, completely, wiped it out, cured the ticks.

• 9:07Regina Barber?

  Cool.

• 9:08Speaker 01

  And Gina, get this. It's not just the western fence lizard. Other small reptiles, like the eastern fence lizard and the southern alligator lizard, they also have this Lyme-killing blood. There's the white-tailed deer, too. And I know some rabbits can adapt after multiple tick bites to cleanse ticks of Lyme.

• 9:23Regina Barber?

  This is so fascinating. Okay, so could we just bring these lizards everywhere and get rid of Lyme disease, like, for good?

• 9:31Speaker 01

  You'd think that would work. I thought the same thing, too.

• 9:34Regina Barber?

  Yeah.

• 9:34Speaker 01

  But I talked to Andrea, and she said when she was in grad school in California, she did this experiment where her team removed the western fence lizards from an area, just to see what would happen.

• 9:43Speaker 02

  We actually found the exact opposite impact. So when we removed the lizards, Lyme disease prevalence and infection went down.

• 9:52Speaker 01

  What? Why? I was confused about this, too. But it actually does make sense.

• 9:57Speaker 02

  What's unique about the California system is that the lizards are so important for feeding the tick. So if you go out and you sample a bunch of animals, which my lab has done, you'll find, you know, a smattering of ticks on wood rats and mice and squirrels.

• 10:15Speaker 02

  On the order of maybe one to eight ticks per animal. But if you look at a lizard, they'll have on average 25, 30, sometimes up to 100 ticks on them.

• 10:25Regina Barber?

  So they really like lizards, I see. Okay, so if they have less to eat, then they might die.

• 10:31Speaker 01

  Right.

• 10:31Regina Barber?

  That makes sense.

• 10:32Speaker 01

  Yeah. In other words, one of the biggest functions of these lizards is being a meal for these ticks to thrive and stay alive and then mate. And detoxing the tick's blood of this Lyme-carrying bacteria is kind of a smaller function.

• 10:48Speaker 02

  I think what it shows us is these systems are incredibly complex and pulling on one thread isn't going to do the thing that you think it will be because it's connected to these other factors and it's just really complicated.

• 11:04Regina Barber?

  Okay, so it's very complicated, but these lizards, they basically clear Lyme disease with their blood. So could we make something similar in a lab, then use it to help defend humans against Lyme disease?

• 11:16Speaker 01

  Probably not, unfortunately, right? Just because like protein works in lizards doesn't necessarily mean it'll work for us humans. But there is good news. What if I told you that scientists are working on a vaccine that could train our immune systems to kill ticks?

• 11:32Regina Barber?

  Great, let's do that.

• 11:34Speaker 01

  So Adela Leva Chavez, she's the medical entomologist, she's working on something like this. It's called an anti-tick vaccine and it hinges on this key fact, that ticks are really slow feeders.

• 11:45Speaker 05

  The feeding process of the tick, depending on the life stage, goes from three days all the way to seven days. So for those seven days, the tick has to be able to be attached to you and not die because your immune system is killing the tick. So what they do is they use their saliva. They inject their saliva into your skin. The saliva will target certain cells, immune cells and cells in your skin and reduce the immune response so it doesn't get killed. The pathogens get a free pass. They go like, yeah, we can infect. The immune system is reduced.

• 12:28Speaker 01

  And so Adela and her colleagues thought, all right, what if we could just get the immune system to recognize and attack the tick?

• 12:37Speaker 01

  Instead of being reduced.

• 12:38Regina Barber?

  Hmm.

• 12:39Speaker 05

  So my laboratory is trying to take those proteins that are being injected into the human.

• 12:48Speaker 01

  The ones that are in the tick saliva, right?

• 12:51Speaker 05

  And instead of them affecting your immune system, decreasing it, we're educating your immune system to recognize those proteins so that they can inactivate them. So that the tick now activates your immune system and then your immune system can kill the tick.

• 13:12Speaker 01

  And all of this is increasingly important, Gina, because tick territory is expanding. Ticks are coming further north to Canada, further west to, say, Minnesota, and even becoming more common down south.

• 13:23Regina Barber?

  Yeah, we talked about this earlier. Do we know why that is?

• 13:26Speaker 01

  Not really. All of the experts told me it could be a number of things. Warming temperatures due to climate change, increased development in land use in once rural and undeveloped areas. Even seemingly harmless things like deer are a major host for these ticks, and they're increasingly found in urban areas. So nowadays, you might find ticks in city parks and green spaces, too. All of that means that even if you weren't living in tick territory before, or if you don't remember doing tick checks in the past, it's probably a good idea to start checking yourself and your clothes for ticks after you've been outside. One of the experts I talked to recommended the Tick app. It has information about tick counts in your local area, instructions on what to do if you're bitten by a tick,

• 14:09Speaker 01

  and even a spot to submit photos and help you ID that tick.

• 14:12Regina Barber?

  Han, this is really good to know. Thank you so much for bringing us the story.

• 14:16Speaker 01

  Anytime, Gina.

• 14:22Regina Barber?

  This episode was produced by Rachel Carlson and edited by showrunner Rebecca Ramirez.

• 14:26Speaker 01

  Tyler Jones checked the facts. Anli Huang was the audio engineer. Special thanks to Maria Dykvaso. I'm Hannah Chin.

• 14:33Regina Barber?

  And I'm Regina Barber. Thanks for listening to Short Wave from NPR.

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