ST. LOUIS — A pair of hunters drove along a rutted gravel road in the forests west of St. Louis in June, a plume of dust trailing behind them.
They hopped out of their SUV, knee-high gaiters cinched tight over their hiking boots, and looked for a spot to lay their trap. Their prey is smaller than an apple seed, hidden in the leaf litter blanketing the forest floor — ticks.
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If they’re lucky, these scientist-hunters will collect a few hundred of the parasitic arachnids by the end of the day, as part of a study tracking tick-borne viruses at Washington University’s Tyson Research Center in Eureka, Missouri.
Several deadly new viruses have cropped up in the Midwest in recent years, including the Heartland virus, first identified in northwest Missouri in 2012. As climate change expands ticks’ ranges and increases how long they’re active each season, scientists say identifying the next generation of tick-borne viruses is crucial.
Cases of tick-borne illnesses have risen in the U.S. in recent years, with more than 50,000 cases reported in 2019. The vast majority are cases of Lyme disease, a illness rarely found in Missouri that is caused by bacteria.
Because newly emerging viruses are thought to be relatively uncommon, finding them hinges on collecting a lot of ticks.
The lone star tick — the most common species in Missouri — is easy to lure in, said Solny Adalsteinsson, an ecologist at Tyson. Unlike other species that cling to plants and wait for an animal to brush past, lone star ticks aggressively seek out hosts, following the puffs of carbon dioxide they exhale.
Adalsteinsson laid a square of white flannel cloth on the forest floor and set a Tupperware container of dry ice in the center.
“The lone star ticks, when they sense you, they’ll just chase you down,” she said. “That’s why these dry ice traps work really well. Sometimes if an area is ‘ticky’ enough, you’ll see them respond immediately to the carbon dioxide.”
About an hour later, the cloth was crawling with dozens of ticks.
Research technician Anahi Aviles Gamboa swiftly stuffed the cloth into a zippered plastic bag, which she’ll later pop into a subzero freezer to be processed at Washington University. So far, the team has analyzed several thousand ticks, testing them for known viruses and possible new variations.
The recent identification of two novel tick-borne viruses — the Heartland virus, first diagnosed in two Missouri farmers in 2012, and Bourbon virus, discovered in 2014 in Kansas — is likely just the “tip of the iceberg,” said Washington University microbiologist David Wang.
“There’s no way that those are the only two tick-borne pathogenic viruses out there,” said Wang, a collaborator on the project. “It’s just that people haven’t been looking.”
There are probably other new viruses transmitted by ticks that have gone undiagnosed over the years, he said, simply because doctors don’t know what they are.
“The classic way that medicine works is you look for the usual suspects,” Wang said. “You can only find what you’re looking for. So when it’s negative for everything, then what do you do? In order to find something that’s not in the usual set, you need to take a different approach.”
Scouting for new viruses
To search for known tick-borne pathogens, including Heartland and Bourbon viruses, as well as possible new ones, the team at Washington University is relying on genetic sequencing techniques.
It’s a time-consuming process that begins with grinding up frozen ticks into a slurry of floating legs and antennae.
“We want to break the ticks up and release the contents,” said Ishmael Aziati, a postdoctoral researcher who has processed thousands of them inside a small lab at Wash U. “Basically we’re just breaking them up using mechanical force.”
Aziati drops small steel balls into plastic tubes containing the ticks, then slides each tube into a vibrating machine. As the beads collide, they pulverize the ticks, while specialized chemicals help extract their genetic material.
The research team will later feed the genetic sequences into a computer and compare them to all known viruses to see how closely they match.
“Sometimes we’ll get something that matches a known virus with only 70% or 50% similarity, and that’s when we start to get excited, because those are clearly different from what’s already in the database,” Wang said. “That’s our starting point to say, here’s what looks like a piece of a new virus.”
Still, finding new viruses is just the first step, he said. The hard part is figuring out which ones could potentially infect humans.
The team has also been collecting blood samples from a small number of staff at Tyson Research Center to test them for potential tick-borne pathogens and look for signs of past infection.
“It’s easy to find 100 new viruses, but it’s really difficult to say which one of those is important,” Wang said. “By developing antibody tests for these viruses and looking at blood from people who have had some tick exposures, we can help prioritize which viruses we should spend more effort on.”
This kind of research is vital in Missouri, said Deborah Hudman, a tick researcher at A.T. Still University in Kirksville, Missouri, who is not affiliated with the Wash U study.
“I’ve done tick research in California and New York, but I’ve never seen anything like the state of Missouri,” she said. “It’s just absurd the number of ticks that are here. We’re in that sweet spot: not too hot, not too cold, not too dry. And we have a lot of wildlife.”
But despite the abundance of ticks, Hudman said there’s a major gap in research here.
She’s currently documenting where different species occur in the state and testing them for bacterial pathogens — basic information that’s important for studying how tick-borne diseases spread. In the past six months, Missouri residents have mailed her more than 12,000 ticks from nearly every county.
She’s also gotten letters from people afflicted with tick-borne ailments, including a rare red meat allergy linked to lone star tick bites. Studying these illnesses can take a lot of time, energy and money, she said, and testing for viruses in particular feels like “looking for a needle in a haystack.”
But, she added, there’s a real need for this work.
“People really do suffer from these tick-borne diseases, and they need more attention,” Hudman said. “There’s just so much we don’t know.”
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