In August 2017, seven cattle, ranging in age from 3 months to 13 years, died on a farm in Virginia after showing signs of weakness and lethargy. All were born and raised on the farm. A month later, another cow in the herd showed signs of weakness, jaundice and severe anemia.
“The herd veterinarian examined the cow and made a preliminary diagnosis of anaplasmosis. However, blood samples were sent off to be tested for anaplasmosis,” said Craig Payne, University of Missouri Extension veterinarian. “It came back negative, but the veterinary pathologist working on this case did a blood smear, stained the slide, looked at it under a microscope and identified what they call piroplasm on red blood cells.”
This led to further investigation, and it was eventually determined that Theileria orientalis ikeda was the cause of disease.
Since then, this disease has been reported in multiple states, including Alabama, Arkansas, Georgia, Iowa, Kansas, Kentucky, Maryland, Missouri, New York, North Carolina, Pennsylvania, Tennessee and West Virginia.
Theileria orientalis ikeda was first detected in Missouri in June 2023 and has since been reported in 60 counties. With the westward movement of this disease, it is critical to understand how it spreads and how to minimize the impact.
How does it spread?
The Asian longhorned tick is the primary vector for Theileria orientalis ikeda, and the tick transmits the organism through its saliva while feeding on cattle.
“The organism infects red blood cells, and those red blood cells are damaged and lost during circulation,” Payne explained. “This is going to create anemia, and there will also be an inflammatory response associated with the infection.”
It may also be transmitted from infected to uninfected animals through biting flies, sucking lice and blood-contaminated equipment, such as needles and tagging tools.
Cattle typically show clinical signs of disease within one to eight weeks of infection. The severity of symptoms varies among animals.
“Keep in mind that the severity of the anemia and the severity of the inflammation is going to dictate what those clinical signs look like,” Payne said. “The reality is that many cattle are not going to show clinical signs, even though they’re infected."
Cattle infected with Theileria orientalis ikeda may exhibit the following symptoms:
- anemia
- depression
- fever
- reduced feed and water intake
- pale mucous membranes
- increased respiration
- late-term abortions
“There is a death loss risk associated with this disease, and normally it’s reported to be between 1% and 5%,” Payne said. “But I am aware of situations where the losses have been much higher. Unfortunately, it happens, but fortunately, not a lot.”
Payne added that the reason some cattle populations are more severely affected is unclear. However, stress can increase the severity of clinical signs.
It is also important to note that any cattle infected with the organism will be infected for life.
“Once an animal is chronically infected, it will unlikely have problems with the disease from that point forward,” Payne said.
How to protect your cattle
The are no antibiotics available in the U.S. to treat theileriosis, so options are limited. Payne recommended supportive care, which includes minimizing stress and handling, providing access to water and palatable feed, and administering anti-inflammatories, if necessary.
No vaccines are available to protect cattle from the disease. Control focuses on minimizing transmission, which decreases the level of exposure in a herd. This is accomplished by controlling insect vectors such as Asian longhorned ticks and biting flies, changing needles between animals, and disinfecting blood-contaminated equipment.
How you manage new additions to the herd also needs to be considered.
“Adding naïve cattle to a herd where the disease is already present increases the risk of disease in those new additions,” Payne said. “The inverse is true. Introducing infected cattle into a herd where the disease is not present places the resident population at risk. How new additions should be managed is a discussion that producers should have with their herd veterinarian.”
As the disease continues to spread westward, it is essential for producers to be aware of the clinical signs of disease and methods of control. Producers should work with their veterinarian to develop a plan that will minimize the impact of the disease.
Anaplasmosis versus theileriosis
The clinical signs of theileriosis and anaplasmosis are similar, but there are notable differences. Craig Payne, University of Missouri extension veterinarian, shared these five differences, but he emphasized that diagnostic testing is the only way to definitively distinguish between the two:
- With theileriosis you can see clinical signs at any age, but with anaplasmosis, those signs are seldom seen in cattle less than 2 years old.
- Late-term abortions are more common with theileriosis.
- With theileriosis, animals do not become aggressive. However, with anaplasmosis, animals in the late stages of disease can become aggressive.
- Ventral edema may be seen with theileriosis.
- Splenic enlargement is not as dramatic with theileriosis.
If your operation has experienced death loss from Theileria orientalis ideka, the USDA Livestock Indemnity Program may be a way to offset some of the financial impact. Payne recommended producers reach out to their local Farm Service Agency for more details.