Tick Check! The Tiny Bloodsuckers In Our Backyards : Short Wave Short Wave is going outside every Friday this summer! In this second episode of our series on the National Park system, we head to Big Thicket National Preserve in Texas. Among the trees and trails, researchers like Adela Oliva Chavez search for blacklegged ticks that could carry Lyme disease. She's looking for answers as to why tick-borne illnesses like Lyme disease are spreading in some parts of the country and not others. Today: What Adela's research tells us about ticks and the diseases they carry, and why she's dedicated her career to understanding what makes these little critters... tick.

Tick Check! The Tiny Bloodsuckers In Our Backyards

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EMILY KWONG, BYLINE: You're listening to SHORT WAVE from NPR.

(SOUNDBITE OF BIRDS CHIRPING)

REGINA BARBER, HOST:

On clear days between October and April in Texas' Big Thicket National Preserve, you can spot groups of researchers wandering the trails.

ADELA OLIVA CHAVEZ: We leave early in the morning, about 8, drive for about two hours until we get to Big Thicket.

BARBER: That's Adela Oliva Chavez. She's a medical entomologist - a field all about the tiny critters that make us sick. And she wears a pretty specific outfit to hunt for her favorite arachnid - ticks.

OLIVA CHAVEZ: We are wearing light clothes, so something white, something peach, like light color so that if by any chance we get any ticks crawling on us, we can see them.

BARBER: As they walk through the preserve, they do something called dragging.

OLIVA CHAVEZ: So we come with a piece of white cloth that is attached to a piece of wood. It's being dragged on the floor. So it's on the vegetation - on top of the vegetation. And it just passes and brushes through. We count to 10 or a hundred...

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OLIVA CHAVEZ: ...While we walk, stop and check if we have an adult tick. We put it in a vial containing a solution that preserves DNA and RNA.

BARBER: Adela's fascination with ticks began early in her life.

OLIVA CHAVEZ: I grew up in a farm - in a cattle farm - in Honduras. And in the cattle you see a lot of the ticks and also in people. When I was a kid, my twin sister actually fell ill.

BARBER: At the time, doctors didn't know what was making her sister sick. They later determined she had a vector-borne disease, meaning it was transmitted from something like a tick or a mosquito. Adela's sister got better with antibiotics, but the experience stuck with Adela. She dedicated her career to studying these kinds of diseases to prevent this kind of thing from happening to more families.

OLIVA CHAVEZ: They actually have such a big impact in the livelihood of the farmers and also, like, people getting sick with diseases that cannot be diagnosed because nobody knows what they are.

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BARBER: Today on the show, a researcher's quest for accessible solutions for Lyme and other tick-related diseases. I'm Regina Barber, and you're listening to SHORT WAVE, the daily science podcast from NPR.

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BARBER: So first, let's talk about what's happening with ticks in the wild. There are many different kinds of ticks around the world, and only a few species suck on us humans and spread disease.

OLIVA CHAVEZ: In the case of the United States, the most prevalent vector-borne diseases are tick-borne diseases. From those, the most commonly diagnosed disease here in the United States is Lyme disease.

BARBER: Lyme disease is generally found in black-legged, aka deer ticks in the eastern half of the U.S. Once an infected tick bites another animal, like a human, it takes about a day for the bacteria to spread. Though ticks can suck out nutrients much longer than that.

OLIVA CHAVEZ: Ticks feed on you for up to seven days and just stay there until they get completely engorged.

BARBER: For reference, they start as small as a poppy seed and feed up to...

OLIVA CHAVEZ: One hundred times their weight in blood - so you can see, like, they are about, like, a quarter size.

BARBER: Adela says it's crucial to remove the tick in the first 24 hours. If you don't remove the tick in that window, the bacteria can spread. And then, Adela says, Lyme disease can take hold and be tricky to catch. Many people don't realize they have it.

OLIVA CHAVEZ: Unless you have one particular sign that is what we call the bull's eye - it's where the tick bites you. As the bacteria is disseminating in your skin, it produces an inflammatory reaction. So you see redness, like, a circle that is red. And this process takes some time because there are changes that happen in the tick.

BARBER: And while they're feeding, molecules in their saliva trick your body's immune system.

OLIVA CHAVEZ: So imagine, like, when you have a cut, you have a lot of immune cells that come and try to fix where the cut is, right? In the case of the tick, the tick tells it, hey, I want to feed, so stop. You are not fixing anything.

BARBER: Like Jedi mind tricks.

OLIVA CHAVEZ: Yeah - like Yoda that telling them something like fix cut not or something like that.

BARBER: (Laughter).

We mostly think about this as an East Coast problem, but...

So I'm scared of ticks. I'm so glad you said that they're mostly in the Northeast 'cause I live in the Pacific Northwest.

OLIVA CHAVEZ: Oh, well, you have another one over there.

BARBER: No.

OLIVA CHAVEZ: So the species you have would be Ixodes pacificus.

BARBER: Ticks are all over the country. Some ticks and the Lyme and other diseases they carry - they've started popping up in unusual places.

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BARBER: Take the black-legged tick. It's expanding through the Northeast, Upper Midwest and mid-Atlantic. One place they're not - Big Thicket National Preserve in Texas, which is exactly why Adela's comparing ticks from Big Thicket to ticks in, say, Minnesota. She wants to understand why Lyme disease infections are rising with the spread of these black-legged ticks and not with the ones in Big Thicket. It starts with how ticks find their hosts.

OLIVA CHAVEZ: Ticks have this behavior that is called questing. That's how they get into their hosts. And this questing behavior - what it is is ticks go up into the vegetation - like a piece of grass, something that they go up to - and then they start waving their front legs. Then as the host passes, they latch with the front legs, and that's how they get into hosts.

BARBER: Adela found that this questing process is different depending on where the ticks live.

OLIVA CHAVEZ: In Minnesota, they will go up to the top of the vegetation and then start doing the questing and start waving their legs from side to side. The ones here in Texas don't do that. And we believe that is because it's so hot here that they would lose too much water if they were in - up in the vegetation. So they are staying low in the vegetation. So when a human is going hiking, all happy into the trails, they are less likely to encounter ticks if they do it here in Texas than if you do it up north, in the Northeast or in Minnesota.

BARBER: Adela also says black-legged ticks in Texas feed on lizards, which are less likely than small rodents to get infected with the bacteria that causes Lyme disease. If fewer ticks are infected, they're less likely to transmit the disease to humans later.

OLIVA CHAVEZ: In Minnesota, you can find up to 50% of the ticks infected with something. Here in Texas, the infection rates are a lot lower.

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BARBER: This difference in how they act isn't the only thing contributing to the spread of ticks and tick-borne diseases.

OLIVA CHAVEZ: Global warming, changes in human behavior and also the way that we are killing the predators that will normally keep deer and mice population down because if there are not hosts for the ticks to feed on, then the population of the ticks do not thrive.

BARBER: Black-legged ticks tend to like hotter, more humid climates. So as climate change intensifies, we might see longer tick seasons. Add in a growing population headed out to the suburbs...

OLIVA CHAVEZ: Before we tended to live in, like, cities only. Now we're living in suburban areas, so we are coming into the areas where the ticks are. So you can go to your backyard and actually get ticks in your backyard.

BARBER: Recently, because of her large body of work, the United States Department of Agriculture awarded Adela a grant to start developing a vaccine for cattle to protect against the cattle fever tick. Her ultimate goal is to create a vaccine that will protect humans from ticks, too.

OLIVA CHAVEZ: And once we see what proteins and what candidates work with cattle, it will be a proof of concept that we can do this - we can kill ticks feeding on invertebrate animal - to then move into humans, developing a vaccine that will prevent tick feeding on humans and the spread of different pathogens in humans.

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BARBER: This episode was produced and fact-checked by Rachel Carlson. It was edited by Rebecca Ramirez. The audio engineer for this episode was Andie Huether. Our newsroom higher-ups are Terence Samuel, who's our vice president and executive editor, Edith Chapin, who's our vice president and executive editor-at-large, and senior vice president Nancy Barnes. Before we head out, a quick shoutout to our SHORT WAVE+ listeners. We appreciate you and thank you for being a subscriber. SHORT WAVE+ helps support our show. And if you're a regular listener, we'd love for you to join so you can enjoy the show without sponsor interruptions. Find out more at npr.plus.org/shortwave. I'm Regina Barber. Thanks for listening to SHORT WAVE, the daily science podcast from NPR.

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