Ecological Complexity and Future Prevention

You're listening to Shortwave from NPR . Hey Shortwavers Regina Barber here, and today I am joined by producer Hannah Chin. Hey, Hannah. Hey, so today I want to start our episode with a mystery . Ooh . It starts the way a lot of old mysteries start with a group of kids in a tiny town in the middle of the wood. Oh, it's a horror movie. In the late nineteen seventies, a small cluster of children came down with arthritic symptoms and children aren't supposed to have arthritis . So this sort of alerted public health officials to something kind of funny going on. This is actually terrifying. Like where did these kids live? 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, okay, 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 foremost. It wasn't until the early nineteen eighties that the organism was identified as Berlia Bergdorfi, a spiracetal bacteria that was transmitted by ticks. This is Andrea Sway. She's a disease and factory 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 we noticed it and like had the tools to track it down. 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. And nowadays, Connecticut is still a hotot forsp Lyme dis ease. In fact, if you look at a map of Lyme cases, I actually looked at the CDCs just now, the vast majority of them, like more than ninety five percent, are in the Great Lakes area and the Northeastern US. So we're talking about the upper right hand corner of the United States. 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 lime country is expanding. So today on the show, we're doing a tick check, short wave style . 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. Plus, why their territory is spreading, maybe even into your backyard. You're listening to Shortwave, the science podcast from NPR Follow us to make sure you never miss a new episode. New ones drop every Monday, Tuesday, Wednesday, and Friday. Okay, Gina, so we're going to start with tick one hundred one. Get ready to be a little bit grossed out. I love school. Let's do it. To start, these arachnids have four stages of development egg, larvae, nymph, and adult. After they hatch, they need to have blood meals at every single stage in order to survive. Right. It's these blood meals that that's when they get infected with the disease. Exactly. And there's only two kinds of ticks that carry lime in the U. S. There's the blacked legg tick or deer tick and the western black legged tick. Okay, I don't know why that makes me feel a little better. And to be clear, these ticks aren't born with lime. They only get infected when they feed on an infected animal, like a bunny or a bird or a deer, or a human. Okay. And I asked Adella Oliva Chavez about this process. She's a medical entomologist at the University of Wisconsin Madison. The bacteria will come with the blood that the ticks are taking , it will go to the meat god that is the stomach of the tick . And in the stomach of the tick they bind to the epithelial cells. So the lining of the gut of the tick , they will bind to that lining . So this bacteria that causes Lyme disease, it goes straight to the tick stomach lining and it just camps out there. Exactly. And again, ticks only feed once per developmental stage, right? So say the larvae feeds on an infected host, that same larvae 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 . When the tick then bites the 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 thirty seven degrees. And Adela is using Celsius here. So it's like ninety eight point six degrees Fahrenheit. So that's the temperature of a human, right? When I'm healthy. Exactly. And this temperature trigger, right? Okay, 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. So this is all happening during like the feeding process where the tick is like on me on us. Yes. And that's why the CDC gives this recommendation that you should try to find and remove ticks if possible within the first twenty four hours. 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 it tick in those twenty four hours , you won't get sick. And that's how ticks transmit lyme disease. 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? Yeah, I wanted to know this too. So I talked to a disease ecologist. Her name is Jean Sou 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. Yeah, that's a lot. 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. In the north, forty percent to sixty percent of the adult ticks are infected with the lime bacteria, depending on where you are. But in the south, if you look at the adult ticks, it's very low, like, zero point two percent in a place where we collected a lot of these ticks. 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. 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. Antics 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 a 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 super power . They can clear the ticks systems of lyme dis ease. That's so cool. Yeah. So back in the nineteen nineties, 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 the specific protein in the lizard's blood that killed the Lyme disease bacteria, Berelia Brudorferi completely wiped it out, cured the ticks. Cool. And Dina, 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 a white tailed deer too, and I know some rabbits can adapt after multiple tick bites to cleanse sticks of lyme. This is so fascinating. Okay, so could we just bring these lizards everywhere and get rid of lyme disease like for good? You'd think that would work. I thought the same thing too. Yeah, 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. We actually found the exact opposite impact. So when we removed the lizards , lyme disease prevalence and infection went down. What? Why? I was confused about this too, but it actually does make sense. 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 squirrel s on the order of maybe one to eight ticks per animal. But if you look at a lizard , they'll have on average twenty five, thirty, sometimes up to one hundred ticks on them. So they really like lizards, I see. Okay, so if they have less to eat , then they might die. Right. That makes sense. Yeah. In other words, one of the biggest functions of these lizards being a meal for these ticks to thrive and stay alive and then mate . And detoxing the tick's blood of this lime carrying bacteria is kind of a smaller function. 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. 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 than use it to help defend humans against Lyme disease? Probably , unfortunately, right? Just because 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 system s to kill ticks. Great, let's do that. So Adella Liva Taves, 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 . 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 the saliva into your skin, that's 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 . And so Adella and her colleagues thought, all right , what if we could just get the immune system to recognize and attack the tick instead of being reduced. So my laboratory is trying to take those proteins that are being injected into the human . The ones that are in the text saliva, right? 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. 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. Yeah, we talked about this earlier. Do we know why that is? Not really ? All of the experts told me it could be a number of things warming temperatures due to climate change, increased development and 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 are a, instructions on what to do if you're bitten by a tick, and even a spot to submotos and help you ID that tick. Han, this is really good to know. Thank you so much for bringing us the story. Anytime, Gina . This episode was produced by Rachel Carlson and edited by showrunner Rebecca Ameris. Tyler Jones checked the facts. Ann Lee Huang was the audio engineer. Special thanks to Maria D ick Vosser. I'm Hannah Chin, and I'm Regina Barber . Thanks for listening to Shorewave from NPR.