FAYETTEVILLE, Ark. — As cases of a deadly cattle disease rise in Arkansas, researchers with the Arkansas Agricultural Experiment Station are testing two treatments they hope will help ranchers protect their herds.
The disease is bovine theileriosis and is caused by the parasite Theileria orientalis Ikeda, carried primarily by the invasive Asian longhorned tick. Arkansas cases of the disease increased drastically in 2025, just a year after being confirmed in the state, said Emily McDermott, an assistant professor in the department of entomology and plant pathology for the experiment station, the research arm of the University of Arkansas Division of Agriculture.
No approved drugs or vaccines to treat or prevent the pathogen are currently available in the United States, but research on the two methods to control it is now underway at the experiment station thanks to a two-year, $492,218 grant from the U.S. Department of Agriculture’s National Institute of Food and Agriculture.
Arkansas cattle ranchers are reporting “significant losses of the herd, resulting in economic hardship,” said McDermott, project director of the NIFA grant titled “Rapid response strategies to mitigate Theileria orientalis Ikeda spread in Arkansas.”
As part of the research, McDermott and her collaborators will evaluate a prescription anti-tick vaccine from the company Medgene for long-term protection and the slow-release parasiticide eprinomectin, used with currently labeled acaricides for the Asian longhorned tick. The eprinomectin will be compared to two available pyrethroid products.
Both treatments are commercially available and can be adopted quickly by producers, she said.
In cattle, the symptoms of bovine theileriosis tend to mirror those of anaplasmosis, a bacterial disease also transmitted by ticks to cattle. Symptoms in the cow may include weight loss, reduced milk production, loss of appetite, anemia and reproductive losses.
“One of the tricky things about Theileria is that it looks so much like anaplasmosis that I think a lot of producers might not be aware they have a new disease,” McDermott said. “We’ve heard the same story a lot over the last year … ‘I had a bunch of cows die, and I thought it was anaplasmosis, but it was weird.’
“The more that we’re getting information out there about Theileria , a lot of producers are starting to think that something else was going on,” she said.
A major difference between the two diseases is that bovine theileriosis can cause symptoms in cattle of any age, whereas anaplasmosis symptoms and illness typically occur in older cattle, said Kelly Loftin, extension entomologist for the Division of Agriculture and a collaborator on the research.
Two genotypes of the parasite T. orientalis — Ikeda and Chitose — have been confirmed in Arkansas. The more harmful of the two genotypes is Ikeda, which can kill cattle by attacking blood cells. The parasite is not known to cause disease in animals other than cattle, McDermott said.
In preliminary research at the experiment station’s Savoy Research Complex in Fayetteville, theileriosis from T. orientalis Ikeda is thought to have contributed to poor reproductive efficiency and a drop in weaning weights, said Jeremy Powell, a veterinarian, professor in the department of animal science for the Division of Agriculture, and collaborator on the research.
Infections of T. orientalis Ikeda have been reported to kill an average of 1 to 5 percent of infected cattle, but can be as high as 50 percent, according to a January 2024 USDA Animal and Plant Health Inspection Service fact sheet .
“It’s hard to think of a tick-borne cattle pathogen that’s had this much of an impact in the United States since Texas cattle fever, which became a major issue in Arkansas from the pre-Civil War era until the mid-20th century,” McDermott said.
To clear Arkansas of Texas cattle fever, the state also partnered with the USDA from 1907 to about 1943.
The NIFA grant also provides funding for routine outreach through the Division of Agriculture’s Cooperative Extension Service to educate county extension agents, ranchers and veterinarians on the risk and transmission of the parasite.
Asian longhorned ticks were first noticed in Arkansas eight years ago, with the first confirmed report in the United States being just a year prior in New Jersey. The ticks reproduce asexually and can lay thousands of eggs at a time.
The first bovine theileriosis cases in Arkansas from T. orientalis Ikeda were confirmed in 2024 in two Arkansas counties, Loftin said. Since then, the disease has been confirmed in 15 Arkansas counties across the state, with 10 counties holding established Asian longhorned tick populations. Loftin said the numbers are anticipated to grow.
Some counties have both ticks and confirmed disease cases, while others have the disease and no ticks, suggesting the disease is moving with cattle after they are relocated, Loftin added.
McDermott said questions remain about whether other insects might also be able to transmit the pathogen mechanically.
“Mechanical transmission, I always say, is kind of like a dirty needle with wings,” McDermott said. “ Theileria can be mechanically transmitted because it is a blood-borne pathogen, and so theoretically, anything that breaks the skin is a means to transmit this. Things like horse flies are biting the animal and then quickly moving to another animal to bite, and that’s where there’s the potential to move that pathogen between animals without it actually infecting the insect.”
Biological transmission, as opposed to mechanical transmission, is when the vector is an active and essential part of the pathogen’s life cycle. Once the vector acquires the pathogen, usually through a blood meal, the disease-causing agent must multiply, develop, or undergo crucial life-cycle stages inside the vector before it can be transmitted to a new host.
Instructions on taking blood samples to limit unintended mechanical transmission are part of the outreach.
“There’s a whole lot of interest, and we have a dedicated website that we’re going to continue with this study,” Loftin said. “We’ll also do a few field days regionally that will involve showing the different treatment techniques for the tick and passing out free needles.”
Loftin has been sharing information about the tick and disease through a webinar series and the “Asian Longhorned Ticks & Theileriosis in Arkansas” website.
This work is supported by the Rapid Response to Emerging and Re-emerging Pest and Disease Events program, project award no. 2026-68019-46340, from the U.S. Department of Agriculture’s National Institute of Food and Agriculture.
The departments of entomology and plant pathology and animal science are part of the Division of Agriculture and the Dale Bumpers College of Agricultural, Food and Life Sciences at the University of Arkansas.
The mention or use of product or trade names is for informational purposes only and does not imply endorsement by the University of Arkansas Division of Agriculture or a preference that excludes other suitable products.
To learn more about ag and food research in Arkansas, visit aaes.uada.edu . Follow the Arkansas Agricultural Experiment Station on LinkedIn and sign up for our monthly newsletter, the Arkansas Agricultural Research Report . To learn more about the Division of Agriculture, visit uada.edu . To learn about extension programs in Arkansas, contact your local Cooperative Extension Service agent or visit uaex.uada.edu .
The University of Arkansas Division of Agriculture’s mission is to strengthen agriculture, communities, and families by connecting trusted research to the adoption of best practices. Through the Agricultural Experiment Station and the Cooperative Extension Service, the Division of Agriculture conducts research and extension work within the nation’s historic land grant education system.
The Division of Agriculture is one of 22 entities within the University of Arkansas System. It has offices in all 75 counties in Arkansas and faculty on three system campuses.
Pursuant to 7 CFR § 15.3, the University of Arkansas Division of Agriculture offers all its Extension and Research programs and services (including employment) without regard to race, color, sex, national origin, religion, age, disability, marital or veteran status, genetic information, sexual preference, pregnancy or any other legally protected status, and is an equal opportunity institution.
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Media Contact:
John Lovett
U of A Division of Agriculture
Arkansas Agricultural Experiment Station
(479) 763-5929
jlovett@uada.edu