The exotic Asian longhorned tick: The new tick in town
By MWI Animal Health
Kevin Lahmers, DVM, PhD, never set out to become an expert on the Asian longhorned tick. However, the veterinary pathologist at the Virginia-Maryland College of Veterinary Medicine at Virginia Tech University received a request a few years back asking if he wanted to look at some ticks.
"Sure," he responded facetiously. "Who wouldn't?"
Life can take people in directions they never anticipated, and the ticks were like nothing he'd ever seen before. Thus began his journey into uncovering the mysteries of the exotic Asian longhorned tick (Haemaphysalis longicornis), the new tick in town.
An exotic tick and theileria, an exotic disease
It's a journey that continues as researchers across the United States work to learn more about the Asian longhorned tick (ALT) and the disease it transmits. For livestock, that disease is theileria, specifically Theileria orientalis Ikeda. As the name suggests, both the tick (and the disease it spreads) are endemic in Japan, Korea, China, and elsewhere in the East Asian region. Before coming to the mainland, the tick was — and is — common in Hawaii. In their native region, both the tick and theileria have been on the scene for a while.
In the contiguous United States, however, the Asian longhorned tick and Theileria orientalis Ikeda present a new challenge. The tick was first documented when it arrived in the United States by hitching a ride on a sheep. Lahmers explains, "It was first identified in New Jersey in 2017; then we found it in Virginia in 2018. But tracing back, we may have had this tick in the United States since 2010 and it was misidentified as the rabbit tick."1
Theileria is a protozoan parasite, and there is no approved treatment or vaccine, says Kathy Simmons, DVM, Chief Veterinarian, National Cattlemen's Beef Association (NCBA). Though the ALT is likely the main vector for the disease, it can spread through anything that transfers blood, such as insect bites and even common needles, according to Lahmers. Typically, clinical signs of theileria will appear from one to eight weeks after infection.
Tick-sized challenges
The exotic tick presents a number of challenges. The adults are very small, about the size of a sesame seed, Simmons says, so they are sometimes hard to detect. Juvenile stages — larvae and nymphs — are so small they may go unnoticed or resemble tiny, fast-moving spiders.2
What's more: Though it's a three-host tick, all three life stages are sometimes found at the same time, even on the same animal. The adults of this exotic tick typically feed on the ears and flank, says Lahmers. And the ticks can infect an animal by the thousands.3
Then there's this: This exotic tick can reproduce asexually. "All of the ticks that have been found in the U.S. are female," according to Lahmers. The female clones herself, laying 2,000+ eggs at a time that hatch without fertilization.
And it's tough to kill. Without suitable hosts, tick larvae can survive on the ground and vegetation unfed for 217 days, nymphs for 263 days, and adult females for 249 days.4
It's also not choosy about its hosts. "We've seen at least 25 different hosts in the United States, including birds," Simmons says. "So the potential for this tick to spread is ever-present." As of this writing, the tick has been found in 18 states, mostly in the East and South, and as far west as Missouri and Kansas.
"Right now, it seems wherever the tick is going, theileria is probably going to follow," Lahmers says. Models have shown that a suitable environment for the exotic tick exists east of the Mississippi river, north as far as Michigan and Wisconsin, and on the West Coast up into British Columbia, he adds. Nine states have reported theileria infections in cattle — Virginia, West Virginia, Kentucky, Tennessee, North Carolina, Pennsylvania, Maryland, New York, and Kansas.
Theileria symptoms are similar to anaplasmosis, Lahmers says. "You're going to get a fever, anemia. The major clinical sign we see is jaundice." Lethargy and possible abortions are also indicative.
Producer experience
Beyond the fact that the ALT was present in the United States long before anyone identified it, the disease was likely misdiagnosed as well. Steve Hopkins of Louisa, Virginia, runs 300 brood cows on six different farms and first felt the blow of theileria in 2018 in one pasture on one farm. "It has a lot of similarities to anaplasmosis, and I've had anaplasmosis on this farm for years," he says.
"I would have cows go down and I tried treating them with antibiotics, working with veterinarians, and nothing responded."
In that particular herd, Hopkins lost 10 percent of his cows. The disease occurred at the end of calving, so he lost a total of 20 percent of his calves that either hadn't been born or were stillborn.
In the months following, news of theileria began to spread, so Hopkins tested cows from each of his six herds and found a 95 percent infection rate. That's not surprising, Lahmers says. When livestock get the disease, they persistently get infected and thus become resistant to future infections.
The problem, Hopkins found, is introducing naive cattle to an infected herd. The following year, he bought 22 cows to replace those he lost to the disease. They were artificially bred and introduced to the herd five weeks before calving. "The ones I had in the herd had built up immunity, and I didn't have a bit of problem with them. But I lost two of those (new) cows and then I lost another six calves."
That's another difference between anaplasmosis and theileria. Anaplasmosis only affects adult cattle; theileria can also affect calves. That the disease will cross the placenta and infect the fetus is unlikely, "so you have a new population of naive animals in endemic areas every year," Lahmers says.
Widespread tick prevalence
Just like Hopkins, Woodworth says that though almost all his cattle have gotten infected with the ALT, a theileria outbreak only occurred in one pasture. "There would have been about 160 cows total on that farm, but it was isolated to one group."
In Hopkins' opinion, stress is a factor in whether or not theileria rears its ugly head. "If they're infected at a time when they're not going through stress, then they can build up immunity to it." He introduced those 22 naive cows into an endemic herd five weeks before they were due to calve, which is stressful for a cow. "It takes the disease about five weeks before it really affects them," he says.
According to Lahmers, theileria seems seasonal. "In this region, we have fall and spring calving, and it seems to match up with calving." Beyond that, he says the disease can also present itself during times of heat stress or if cattle are on a low plane of nutrition.
But be forewarned: Theileria is a silent killer. "The cows that we lost showed very few symptoms before they died," Hopkins says. "Your first one will just be a dead cow. They can look normal an hour before and be dead an hour later. And then in some cases, you'll see symptoms. They'll get a little slow or they'll go down and die probably within 48 hours."
Beyond the disease, severe anemia is also a possible issue. With 2,000 or more ticks all drawing blood meals from a single animal, overwhelming blood loss — also known as exsanguination — can occur.
Control
Though it's unlikely — maybe even impossible — to eliminate the ticks after the cattle and pastures have become infested, they are still controllable. According to Mike Catangui, PhD, an entomologist, parasitologist, and manager of MWI Animal Health Technical Services, any product that controls other species of hard-bodied ticks will control Asian longhorned ticks.
That's because, if there's any good news in this, Asian longhorned ticks haven't shown resistance to the commercially available insecticides that control ticks, Lahmers says.
"So, bottom line, we're not short on products," Catangui says. He recommends spray-on insecticides, either synthetic or natural. "I think they will be very effective against the ticks, and the coverage will be a lot better because you're spraying the entire animal." Beyond that, he recommends an oil-based spray-on product.
Woodworth and his veterinarian consulted with Catangui for control options, sprayed his cattle with a pyrethroid, and saw success. "For us, it's a challenge because of the number of cows that are spread out, although I'd turn around and say I've been pretty impressed taking a side-by-side, a sprayer, and some alfalfa in small squares and spreading them out, how well I could get a group of cows covered on pasture," he says. "I'd say I get a 90 percent job done."
In addition, Woodworth confirmed what published U.S. Department of Agriculture research has found in controlling cattle fever ticks along the U.S.-Mexico border. Though he lost cows to theileria, all his calves survived. "The calves were treated with LongRange® going into the pasture," he says, “and we did not see the longhorned ticks on calves like we did on the cows."
According to Catangui, systemic deworming products are not labeled for ticks but have proved effective against hard-bodied ticks like the exotic ALT. So, if a producer wants to use a dewormer specifically for tick control, either pour-on or injectable, a veterinarian will need to write an extra-label prescription, Catangui stresses.
Pasture management can also be effective in controlling this tick. "One of the things we can do to limit the number of ticks is limit their environment," Lahmers says. "These tend to be in grasslands. And if we keep the pasture shorter, there isn't the humidity at the base of the plants to allow [the ticks] to grow and survive."
Indeed, Woodworth says the grass got ahead of the cattle in the pasture where his cows died, leading to much higher tick numbers.
Though the exotic Asian longhorned tick is highly prolific and spreading rapidly in areas where the climate is suitable, tick control and disease prevention are still possible, according to Fred Gingrich, DVM, executive director of the American Association of Bovine Practitioners (AABP). Speaking during an AABP podcast on the Asian longhorned tick, he said prevention is critical to the disease.1
"Make sure you're supporting the animals in the herd with good nutrition, good mineral packs, and making sure that you're minimizing stress as well as using tick control and good pasture management."
References
1Theileria orientalis and the Asian longhorn tick. Have You Herd? American Association of Bovine Practitioners podcast, September 6, 2021. https://www.buzzsprout.com/814177/9084815-theileria-orientalis-and-the-asian-longhorn-tick
2Asian Longhorned Ticks in Ohio. Ohioline: Ohio State University Extension. Feb. 2, 2022. https://ohioline.osu.edu/factsheet/vme-1035
3National Cattlemen's Beef Association webinar. Ticks — What are they? How they can affect livestock and how to effectively manage them. August 23-24, 2022, Day one: www.youtube.com/watch?v=FIcdEl0qfqs; day two: www.youtube.com/watch?v=4y5SpflOIfM
4Mike Catangui, PhD. Take note of the invasive, exotic Asian longhorned tick. MWI Animal Health, Messenger Focus: Cattle Producer, Summer-Fall 2022. https://www.mwiah.com/our-insights/take-note-of-the-invasive-exotic-asian-longhorned-tick
The Australian experience
Though a relative newcomer to the U.S., the Asian longhorned tick (ALT) has made its home in Australia for 120 years, according to Matt Playford, DVM, a consulting veterinary parasitologist and head of Dawbuts Pty. Ltd., a veterinary research and diagnostic laboratory in Sydney. Speaking during a 2022 two-day NCBA webinar, "Ticks: What are they? How they can affect livestock and how to effectively manage them," he said the ALTs made their way to New Zealand, and close behind came theileria.
However, for 100 of those years, the genotype of theileria the ticks spread in Australia was benign. Then the Ikeda genotype popped up and made its presence known. "Nationally, the costs of theileriosis are estimated at about $18 million (AUS)," Playford says. "That's an important figure to establish as a benchmark because even though we have occasional outbreaks still, the disease appears to have stabilized."
Australian authorities found it impossible to stop the spread of the ticks and the disease. In the endemic area along its eastern seaboard — an area that covers about 3,000 miles — most or all of the livestock are consistently infected and thus resistant to the disease.
"One problem we do have with theileria is that most of our animal health funding is arranged through state-based authorities. We don't have great communication between the states, and so each state is very good at managing their own disease outbreaks and resources but not that great at sharing it," Playford says.
"Our extension message for producers is, use tick control with acaricides with tick side treatments in spring, summer, to prevent the buildup of numbers on cattle, using products that work in your area. You can use pasture management to reduce the risky habitat, particularly to restrict the most susceptible members of the herd, particularly the calves that have been never previously exposed to those high-risk paddocks," he says.
"Manage the calves carefully during that critical 2-to-6-month age bracket, treat all your introductions, and do quarantine treatment when you are bringing in cattle, and check farm history and cattle before sending or bringing in," he adds. "It's possible to do a bit of due diligence on the cattle that you are purchasing to see if they come from an area that has either ticks or history of theileriosis. Make the best use of your clinical veterinarians and your laboratories for diagnostics and for developing biosecurity plans."
For details on the Australian experience of Asian longhorned ticks, go to www.paraboss.com.au
