Theileriosis produces symptoms similar to anaplasmosis, another tick-borne disease familiar to many cattle producers. Infected cattle may experience 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.’”

Kelly Loftin, extension entomologist with the Division of Agriculture and a collaborator on the project, said one key difference is that bovine theileriosis can cause illness in cattle of any age, while anaplasmosis typically affects older animals.

Two genotypes of the parasite, Ikeda and Chitose, have been confirmed in Arkansas, including Logan, Franklin, and Johnson Counties. Ikeda considered it more harmful because it attacks blood cells and can be fatal.

Researchers say infections caused by the Ikeda genotype typically kill 1 to 5 percent of infected cattle but have reached mortality rates as high as 50 percent in some outbreaks.

“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,” McDermott said, noting that Arkansas partnered with the USDA for decades during the first half of the 20th century to eradicate that disease.

The grant also includes funding for outreach through the Division of Agriculture’s Cooperative Extension Service to educate county extension agents, ranchers and veterinarians about the disease and its transmission.

The Asian longhorned tick was first confirmed in the United States in 2017 and in Arkansas in 2018. The first Arkansas cases of bovine theileriosis caused by Theileria orientalis Ikeda were confirmed in 2024.

Since then, the parasite has been confirmed in 15 Arkansas counties, while established Asian longhorned tick populations have been identified in 10 counties. Researchers expect those numbers to continue growing and say confirmed disease cases in counties without established tick populations suggest infected cattle are carrying the parasite as they are moved from place to place.

Researchers are also investigating whether insects such as horse flies may be capable of mechanically transmitting the blood-borne pathogen between animals.

Loftin said the Division of Agriculture will continue providing information through webinars, field days, and its “Asian Longhorned Ticks & Theileriosis in Arkansas” website as the study moves forward.