Theileria: U.S. Cattle Producers Brace for Spread of a New Tick-Borne Disease


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Originally discovered in 2010, the Asian long-horned tick has now been found in 18 states and as far west as Arkansas and Missouri. That’s particularly troubling for cattle producers since the tick is a known carrier of Theileria orientalis, which can infect cattle and cause the disease theileriosis. The disease can be severe and does not currently have an easy route of prevention or treatment.

“The fear is that this disease is carried by a tick that’s known to be moving east to west,” explained Gregg A. Hanzlicek, DVM, Ph.D., clinical associate professor at Kansas State University. “It is not known for sure, but some research suggests lice and possibly mosquitoes can carry it. So, there’s a big fear about it spreading across the country.”

Disease transmission and signs

At this time, researchers believe only the Asian long-horned tick can carry Theileria orientalis. While there are 11 T. orientalis genotypes, only two are considered to be pathogenic in cattle.

“The tick does not require males to reproduce, and they can produce lots and lots of ticks and spread easily in a herd,” Dr. Hanzlicek said.

Theileria sporozoites are transmitted while the tick feeds on cattle and initially infects white blood cells. Later, sporozoites are released and infect red blood cells, which are destroyed by the spleen. This process results in clinical signs such as anemia, abortion, fever, and weakness.

Most animals recover and become life-long carriers. Clinical signs can reoccur in carriers during times of stress, such as late gestation, lactation, and transport.

“The No. 1 disease in cattle theileriosis is mistaken for is anaplasmosis,” Dr. Hanzlicek said. “You have the anemia, pale mucus membranes, open-mouth breathing, reluctance to walk, and third-trimester abortions common with this disease. At this time, we’ve only seen it in a few cow/calf herds.”

Theileriosis is new to the United States, but Australia and New Zealand have struggled with it for years. Based on their experience, all types of herds may be affected, and younger animals can show clinical signs – which makes it different than anaplasmosis.

Prevention and treatment

Normal tick control measures like ear tags, back rubbers, sprays, and pour-ons can help keep ticks off cattle, which could help limit the spread of infection, Dr. Hanzlicek said.

“Use a combination of parasiticides to help control ticks,” he recommended. “The USDA advises producers that pyrethrins can potentially build resistance in ticks. At this point, I tell producers to just pick one and rotate every year to help stop resistance. For instance, use organophosphates one year and macrocyclic lactones another year.”

Treatment for the disease is limited to supportive care. Antibiotics used to treat anaplasmosis, like tetracyclines, are not effective against Theileriosis. Veterinarians may consider an off-label prescription for other antimicrobials, Dr. Hanzlicek advised.

“In Australia and New Zealand, they’ve studied this disease a lot, and some treatments can be successful,” he said. “A lot of animals will get over the disease on their own. Any animal is likely to be a chronic carrier and a source of infection for other animals in the herd. A fair percentage of animals can be chronic poor doers.”


Theileriosis is a reportable disease. Veterinarians or owners who believe their herds are infected should send a blood sample to the K-State Diagnostic Lab, which can test for both Theileria and anaplasmosis in the same sample.

“In our lab, we’ve already diagnosed clinical cases in the Midwest, but they were calves imported from Virginia,” Dr. Hanzlicek said. “We’re anticipating we’re going to start seeing it more in the next five or 10 years.”


Key points:

  • Theileriosis is a tick-borne infection with the disease in cattle identified in 1 state.
  • 18 states identified the tick that carries the disease, including states as far west as Missouri and Arkansas.
  • The majority of infected cattle have limited or mild clinical signs. The symptoms are very similar to anaplasmosis.
  • May see sudden death, especially in late pregnancy and early lactation cows.


Photo credit: Austin