Missouri Cattle Face Rising Threat from Theileria Disease

By Blake Jackson

University of Missouri Director of Veterinary Extension, Dr. Craig Payne, is urging cattle producers to remain vigilant for signs of Theileria orientalis (ikeda), a protozoal organism that has recently been identified in Missouri and poses a growing threat to cattle herds across the state.

The organism infects red blood cells, prompting the animal’s immune system to destroy them, which can lead to anemia. It is primarily transmitted through the invasive Asian longhorned tick.

The disease was first detected in a Virginia cow-calf herd in 2017, with Missouri confirming its first case in Howell County in June 2023. By June 2024, cattle in 10 Missouri counties had tested positive, and by October 1, 2025, that number had surged to 48.

Mild infections can cause fever, lethargy, and pale mucous membranes, while severe cases may result in jaundice, abortions in pregnant cows, and significant weight loss. Although most infected cattle show no symptoms and death losses are usually below 5%, Payne notes that some herds have reported far higher mortality rates.

The disease’s symptoms are often mistaken for anaplasmosis. However, Payne explains that while anaplasmosis rarely affects cattle under two years old, Theileria can impact both calves and adults.

Transmission mainly occurs through the Asian longhorned tick, now found in at least 23 states. Other potential carriers include lice, biting flies, and contaminated tools such as needles or equipment used for castration, tagging, or dehorning. Symptoms typically appear within one to eight weeks after infection, and affected animals remain lifelong carriers.

Currently, there are no approved antibiotics to treat Theileria in the U.S. Supportive care and stress reduction are the primary management approaches.

Payne advises quarantining and treating new animals for ticks, disinfecting shared equipment, and consulting a veterinarian to develop an effective prevention and control plan for each herd.

Photo Credit: gettyimages-r-j-seymour