It didn't take long for one of America's newest tick species to find Thomas Mather.
Mather, an entomologist who specializes in the tiny disease-carriers, had taken a team of scientists to Staten Island, New York, in hopes of collecting at least one Asian longhorned tick.
They were all of 50 feet from their car and had just unfurled a banner of white fabric, known as a tick drag, when the first longhorned tick landed in the fabric. Dragging a nearby patch of grass with the fabric, more longhorned ticks appeared. On a grass blade, Mather spotted an unusual clump and discovered dozens of tiny, seed-like tick larvae waiting for a victim to brush past.
If the Asian longhorned tick was unheard of in America just a few years earlier, it wasn't a stranger here anymore.
Since 2013, the Asian longhorned tick has popped up in at least 11 U.S. states, mostly in the Northeast. Previously limited to Asia, Australia, New Zealand and some Pacific Islands, it likely found several ports of entry to North America, hitching a ride on animals or humans. Its ability to clone itself without a mate made colonizing new locations that much easier.
While the longhorned tick is still feeling out its range in North America, other established tick species are expanding theirs as the climate changes and the planet warms—with consequences for humans, pets and the livestock industry.
Several tick species have spread to new areas of the country, some carrying diseases that can pose serious health risks to humans, including Lyme disease, which can affect the joints, heart and nervous system, and Rocky Mountain spotted fever, a treatable but potentially fatal disease that causes fever and muscle pain.
An aggressive tick called the lone star, which has been creeping north and west from its original habitat, can transmit an illness similar to Lyme disease, as well as pass along a sugar molecule that can make humans develop severe allergies to red meat.
While the total number of tick-related illnesses is difficult to gauge since so many go unreported, the trend is clear. The number of cases of reported tick-borne diseases has been on the rise in the U.S., doubling from 2004 to 2016, and reached a record high in 2017, the latest annual data reported by the U.S. Centers for Disease Control and Prevention (CDC).
Higher temperature associated with climate change is one key factor affecting where, and how fast, ticks colonize new places, the National Climate and Health Assessment says.
Livestock Industry Faces a New Threat
Ticks can jeopardize animals' health, too, and the longhorned species could become a formidable threat to the cattle industry, scientists said.
The longhorned tick is already suspected of killing cattle on farms in three separate Virginia counties by infecting them with Theileria orientalis, a parasite that causes fever, anemia, jaundice, and other symptoms in animals.
In a study published last week about the infections, researchers warned that the tick could put the Virginia cattle industry at risk. Once an animal becomes infected, there is no treatment or cure.
Scientists warn that the longhorned tick could proliferate quickly, and since females can reproduce without a mate, ordinary ways of controlling pest population, like sterilizing males, won't work. A single tick can populate a new location.
"As of right now, we don't have a great way to stop that spread," said Kevin Lahmers, a veterinary pathologist at the Virginia-Maryland College of Veterinary Medicine, who co-authored the new study, published by the CDC.
Several research teams are collaborating with the U.S. Department of Agriculture on research and surveillance of the tick, and researchers are studying the tick's range in other countries to try to determine its potential distribution here.
Ticks in More Places
In general, ticks are expanding their ranges, Lahmers said. In Virginia, 15 to 20 years ago, Lahmers said he only saw dog ticks. Now, deer ticks—which can carry Lyme disease—are the predominant tick species there.
Fluctuating climate and weather patterns can significantly affect diseases carried by ticks, as well as those carried by mosquitoes, said Ben Beard, deputy director of CDC's Division of Vector-Borne Diseases.
With an increasing number of days without frost, for example, the risk of disease transmission starts earlier and extends later into the year. "If you look at climate change models and see how those models are advising those areas of risk, clearly there's an impact that it's having," Beard said.
In Germany, a tropical tick called hyalomma seems to have survived its first winter there, according to Ute Mackenstedt, a professor of parasitology at the University of Hohenheim, Stuttgart. Her team discovered the tick this year too early in the season to have been brought over by migrating birds.
"We expect new ticks species in Germany due to changing weather conditions," Mackenstedt said. She said the hyalomma tick could become the second recently introduced species typically found in warmer conditions to establish a population in Germany, though it's too early to be sure.
Hyalomma can transmit the Ebola-like Crimean-Congo hemorrhagic fever virus, though that virus hasn't yet been found in Germany.
The longhorned tick is able to spread a virus known as SFTS, or severe fever with thrombocytopenia syndrome. It can be fatal, particularly for people over 50, but it hasn't yet turned up in the U.S.
The CDC urges precaution against all tick species, not just the longhorned.
"There's a huge potential here for this tick to further complicate the problems we're already having," said Beard of the CDC. "It's one of those things we can't afford to ignore, but at the same time, we have to work on the problems that are already here."
Crowd-Sourcing Tick Research
Several research efforts are gathering data about the spread of ticks from people who photograph or mail in ticks they've found. Mather runs one of those efforts, a website through the University of Rhode Island called TickSpotters, where his team of researchers fields questions from people who submit photos and samples to be analyzed.
He said there's been a clear increase in submissions over the past few years: From the site's inception in 2014 until 2017, he saw fewer than 8,000 entries. Last year alone, he saw nearly 15,000.
One reason may be that ticks are spreading to new places. Mather said contributors frequently ask, "What's going on? I've lived in this place for 15 years and never seen a tick before."
Building a database of these findings can help researchers understand tick distribution patterns.
"It's people that are encountering ticks a lot more than scientists," Mather said. "TickSpotters has a chance for using the power of the crowd to help understand what's going on."