There’s a new tick crawling around the Eastern half of the United States: the long-horned tick, an invasive species from Eastern Asia that’s been spotted increasingly in urban areas like Staten Island in New York, along with New Jersey, Virginia, and all the way down to Arkansas.
This new tick, however, is a mystery. Its cousins, most notably the black-legged tick, currently inhabit most of the eastern half of the United States; a western variant covers much of California. These two species are linked with Lyme disease, a debilitating illness that can cause arthritis, irregular heartbeat, and inflammation of the brain and spinal cord—among a litany of other issues.
This new long-horned tick, however, has not been shown to carry Lyme disease—yet.
The long-horned and black-legged ticks look quite similar to the naked eye. Males of both species are entirely one color; females of both species sport the same dark circle near their head. The long-horned tick has a slightly redder tint.
But unlike the black-legged tick, whose travel patterns, host preferences, and habitat are well-known, scientists are struggling to answer even the most basic questions about its Asian relative. We don’t yet know how the long-horned tick came to the United States, how it’s spreading, or what it’s capable of doing. All we know is that it’s here.
The first confirmed sighting of the long-horned tick occurred in November 2017, when a colleague told Rutgers entomologist Andrea Egizi that he’d found a tick that “didn’t look like anything he’d ever seen before.” In fact, the colleague had found hundreds of the mystery ticks, burrowed into one New Jersey woman’s unlucky pet sheep.
Egizi took samples of the ticks and ran them through DNA testing. When she first got the results, she was just as confused. “It was a species I’d never heard of before,” Egizi told The Daily Beast.
That didn’t last long. Soon after, Egizi said, she realized what she’d discovered. “Oh boy,” she remembered thinking. “This is big.”
She was the first to find conclusive genetic evidence that the tick—feared in its native habitat for spreading a phlebovirus that kills 15 percent of infected humans—had made it from Asia (or Australia and New Zealand, where it migrated more than a century ago) to America. It was the first new tick species to arrive in 50 years.
But while long-horned tick sightings are now plentiful—Egizi has confirmed nearly 200 sightings since 2017 in New York and New Jersey alone—concrete explanations are not.
Researchers do agree on some things: The tick couldn’t have traveled from as far away as Asia, Australia, or New Zealand without a host to feed on. But there’s little consensus about what that host actually was.
Rick Ostfeld, a disease ecologist at the Cary Institute of Ecosystem Studies, believes the most likely explanation is that it traveled on the hides cattle or livestock. Egizi added that it could also be dogs, which receive less scrutiny from the USDA, or even humans—who receive no tick-based scrutiny at all.
Sam Telford, a professor of vector-borne diseases at Tufts, disagrees with Ostfeld. He thinks it’s “highly unlikely” that the USDA would miss ticks traveling on livestock. “The USDA is highly effective at keeping things out of this country,” Telford told The Daily Beast. “It’s not easy to bring something like a cow in, or a goat.” He has a different theory: “It’s gotta be birds.”
Ostfeld and Egizi think birds are implausible, noting that it would be highly unusual for a bird to fly from Asia, Australia, or New Zealand to the eastern United States. “We don’t have any evidence implicating birds right now,” Ostfeld said.
Despite the confusion, they all agree on one thing: this is conjecture at best, and there’s no evidence to prove one theory over another. “We really don’t know how it got here,” Ostfeld said.
That’s not all. Egizi has found distinct genetic lineages in the ticks she’s tested, which suggest that the critters likely made the transatlantic voyage multiple times, to multiple places. Researchers have also learned that Egizi’s discovery was far from the first time the tick reached U.S. soil: The earliest confirmed discovery, which Egizi said was misidentified before her 2017 findings raised alarm, is from 2010.
This lack of information worries James Burtis, a postdoctoral associate at Cornell’s Department of Natural Resources. “This highlights the need for more tick surveillance,” Burtis told The Daily Beast. “[The tick] has been around this long, and it’s taken us this long to find it.”
Currently, there’s no national tick surveillance program. All of the long-horned tick sightings have been what Ostfeld describes as “opportunistic,” meaning that they’ve only been found when someone has been in the right place at the right time.
“This is not the ideal way of figuring out where this tick is distributed,” Ostfeld said. He noted that it’s quite possible—even likely—that there are long-horned ticks in even more places than we currently know.
Egizi agreed, noting that it’s quite difficult to distinguish the long-horned tick from its more common American cousin, the rabbit tick, without genetic analysis—so unless a researcher knew exactly what to look for, they could easily miss one. In other words, these ticks could be anywhere.
But are they dangerous? Researchers don’t know that either.
The ticks have the potential to harm humans in two ways, Ostfeld explained. They could bring viruses over from Asia, like “severe fever with thrombocytopenia syndrome,” or S.F.T.S., the disease with a 15 percent fatality rate. Or, he added, they could prove able to transmit U.S. based illnesses like Lyme disease.
Egizi isn’t too worried about an S.F.T.S. outbreak. That’s because there’s an extremely small chance that a tick—which only bites three times throughout its life—would manage to bite an S.F.T.S. infected host in Asia, travel to the United States, and bite another human, she said. In New Zealand and Australia, she added, where the long-horned tick has lived for more than a century, there have been no reported cases of S.F.T.S.
Lyme poses more of a risk. While researchers haven’t yet found any long-horned ticks infected with Lyme—or any other pathogen dangerous to humans — there’s no evidence that the ticks are incapable of transmitting those diseases.
But scientists are making headway on that. The CDC, working alongside the USDA and other researchers, are currently in the early stages of what’s called a “vector competency test,” which will begin to answer some of these pressing questions.
There are a few steps to this test, said Charles Benjamin Beard, Deputy Director of the CDC’s Division of Vector-Borne Diseases. First, Beard told The Daily Beast, the CDC’s Atlanta-based tick lab will breed a colony of long-horned ticks that can be sent to other branches, like Beard’s vector-based disease lab in Fort Collins, Colorado.
This process will be quicker than it would for other ticks, Beard added, because the long-horned ticks can reproduce asexually. (This is good news for scientific research, but bad news for humans, Burtis added—asexual reproduction helps the ticks become “very successful, very quick invaders.”) The tick lab will also test each of the ticks to make sure they weren’t infected in the wild. So far, Beard said, researchers haven’t found any evidence of disease.
Once labs like Beard’s have received part of the colony, researchers will infect the ticks with a pathogen. This can be accomplished by allowing the tick to bite an infected host, or by feeding it the pathogen through an infected membrane. They’ll then allow the tick to molt, waiting for it to be ready to feed again. Then, they’ll either have the tick bite a new host, stick it back on a membrane, or put its mouth in a solution that causes it to salivate into capillary tubes.
Beard plans to test the ticks for the dangerous diseases like Heartland virus, Bourbon virus, and Powassan virus, and for the bacteria that causes Lyme disease.
He expects that he’ll receive the tick samples within the year, and that he’ll be able to complete his investigation in the years that follow. He’ll also be testing the ticks for their sensitivity to insecticides like acaricide—which the USDA uses to treat livestock coming into the country—and household insect repellent, to better inform future prevention efforts.
Meanwhile, the CDC will also be working to track the tick’s movements. In the coming months, Beard said, the CDC plans to roll out the kind of national surveillance program that researchers have been seeking, collaborating with state-level departments to develop a country-wide snapshot of tick populations.
Until his team learns more about America’s latest tick invader, Beard suggested the typical preventative measures: insect repellent, drying clothes on high heat, and taking a shower after visiting tick-infected areas.
He added, however, that it’s important to remember the black-legged tick, which we already know is capable of transmitting Lyme. “In some parts of the United States, we see 40-60 percent of collected ticks that are already infected with the lyme disease agent,” he said. “That’s a considerable risk to people who live in those areas. Between 2004 and 2016, the CDC notes that reported tick-borne disease cases have nearly doubled—without any help from the long-horned tick.
“We already have some really good vectors of these diseases,” Beard said. “I think it’s really important to keep this in perspective.”