University of Missouri Director of Veterinary Extension Craig Payne urges cattle producers to watch for signs of disease associated with Theileria orientalis (ikeda), a protozoal organism recently detected in Missouri.

This organism, which primarily affects cattle, causes disease by infecting red blood cells. The immune system attacks the infected cells, resulting in anemia.

First discovered in 2017 in the United States, it has been found in nine states, including Missouri. Payne says that as of March 1, there were six counties in Missouri where cattle have tested positive: Bates, Howell, Oregon, Platte, Shelby and Webster. The first case was detected in Howell County in the summer of 2023.

With mild infections, cattle may show elevated temperature, depression and pale mucous membranes. With severe infections, they can show severe depression and the mucous membranes around eyes and the vulva appear jaundiced with a yellow tinge. Pregnant animals may abort, and animals will lose body condition. Payne notes that most infected cattle never show symptoms, and death loss rates are typically less than 5%.

Symptoms sometimes confused with anaplasmosis

The symptoms are similar to those of anaplasmosis, says Payne. A key difference is that anaplasmosis symptoms are rarely seen in cattle less than two years old, but symptoms associated with theileria are seen in both calves and adults.

Disease is transmitted several ways

The main route of transmission is through the Asian longhorned tick, an invasive species found in 19 states. The tick eats blood meal from an infected animal and then transmits it to other animals through its saliva.  Find more information about the tick on MU Extension’s website. Other insects, such as lice, biting flies and other tick species may be involved in transmission as well.

Blood-contaminated equipment can also transfer the organism from infected to uninfected animals. This would include needles and dehorning, castration and tagging equipment. Up to 10% of calves born to infected animals may carry the organism.

Once transmitted, symptoms appear in 1-8 weeks.

Carriers for life

Infected animals will become lifelong carriers of the organism but are unlikely to show symptoms of disease again. Culling these chronic carriers from a herd may be warranted if disease prevalence is low, says Payne.

Management: Treatment, prevention and control

Antibiotics commonly used to treat and control anaplasmosis in cattle do not appear to be effective against this disease. Recommendations for managing clinical cases include minimizing stress and providing supportive care.

There are currently no vaccines available to prevent the disease, says Payne. The best option is to control Asian longhorned tick populations. Payne recommends a Virginia Cooperative Extension publication on tick management practices for cattle producers, which you can view online here.

Payne also recommends quarantining and treating new animals for ticks. In herds where the disease is already present, changing needles between animals and disinfecting equipment that may be blood-contaminated is good standard practice.

Finally, seek guidance from your veterinarian, who can recommend the best strategy for preventing or controlling the disease in your herd, says Payne.

For more information, see the MU Extension publication “Theileria orientalis: An Emerging Cattle Disease in Missouri,” available free online here.