Theileria orientalis in Oklahoma

By Barry Whitworth, DVM

Over the past few years, veterinarians have detected Theileria orientalis in Oklahoma cattle. Early cases were primarily diagnosed in adult cattle, but more recent Oklahoma cases have been identified in stocker cattle. All cattle producers should be familiar with the clinical signs of this disease and check their cattle daily for signs of trouble.

The first U.S. case of theileriosis was identified in Virginia in August 2017. Those cattle showed weakness and anemia, and veterinarians made an initial diagnosis of anaplasmosis. Blood samples from the animals were tested for Anaplasma, Babesia and Leptospira. Results were negative for all three, but the tests revealed a blood protozoan, later identified as T. orientalis genotype Ikeda. Since that first herd outbreak, the organism has been detected in several states.

Cattle sick with T. orientalis genotype Ikeda may show fever, weakness, anorexia and exercise intolerance. If forced to move, affected cattle may stagger and gasp for air. If stressed excessively, they may collapse and die. On examination, the gums, eyes or vaginal mucosa may appear pale (white) or yellow. Reproductive losses, including stillbirths and late-term abortions, may occur, along with a drop in milk production.

Clinical signs reported in adult cattle in Oklahoma include anemia, sudden death, weight loss, abortion, failure to thrive and failure to calve. In stocker cattle, producers have reported weight loss, anemia, poor performance and sudden death.

Because Anaplasma marginale and T. orientalis genotype Ikeda produce similar clinical signs, telling the two apart can be difficult. One difference is that clinical signs are more common in young cattle infected with T. orientalis than in young cattle infected with A. marginale. Cattle with anaplasmosis also often display aggression, while those with T. orientalis genotype Ikeda typically do not. A laboratory test is required to tell the two diseases apart with certainty.

Researchers have identified Haemaphysalis longicornis as a possible vector of T. orientalis genotype Ikeda. In 2017, the U.S. Department of Agriculture’s (USDA) National Veterinary Services Laboratories (NVSL) confirmed the presence of H. longicornis, commonly called the Asian longhorned tick (ALT) or bush tick. While trying to determine how the tick arrived in the United States, USDA officials discovered it had been present in West Virginia as early as 2010. The tick has now been confirmed in at least 26 states, including Oklahoma. Some evidence suggests other insect vectors may also transmit T. orientalis genotype Ikeda. Needle transfer is another possible route of transmission.

The ALT has been identified in Craig and Mayes counties in Oklahoma. This tick thrives in areas with high humidity, such as wooded regions, brush or tall grass. Ticks are often found where large numbers of wildlife gather, such as along deer trails. Producers can find more information about the ALT on the USDA website at https://www.aphis.usda.gov/livestock-poultry-disease/cattle/ticks/asian-longhorned.

Other countries have developed treatments for T. orientalis, but no approved treatments are available in the United States, and no vaccine exists for this disease. The best defense is prevention: buying cattle free of the organism, avoiding blood transfer between animals and using effective tick control. Producers should purchase cattle from reputable sources. Clean instruments between animals during procedures such as castration or dehorning, and change needles between every animal. Control external parasites with appropriate insecticide treatments. Pasture management also helps, such as rotating cattle away from wooded or brushy areas where ticks thrive. Patch burning may also help reduce tick populations.

Theileria orientalis remains a concern for some cow/calf and stocker producers in Oklahoma. Producers who want more information about T. orientalis genotype Ikeda should contact their local veterinarian or Oklahoma State University County Extension agriculture educator.

References

Hammer, J. F., Emery, D., Bogema, D. R., & Jenkins, C. (2015). Detection of Theileria orientalis genotypes in Haemaphysalis longicornis ticks from southern Australia. Parasites & Vectors, 8, 229.

Oakes, V. J., Yabsley, M. J., Schwartz, D., LeRoith, T., Bissett, C., Broaddus, C., Schlater, J. L., Todd, S. M., Boes, K. M., Brookhart, M., & Lahmers, K. K. (2019). Theileria orientalis Ikeda genotype in cattle, Virginia, USA. Emerging Infectious Diseases, 25(9), 1653-1659.

Spickler, Anna Rovid. (2019). Theileriosis. Retrieved from http://www.cfsph.iastate.edu/DiseaseInfo/factsheets.php.

Watts, J. G., Playford, M. C., & Hickey, K. L. (2016). Theileria orientalis: A review. New Zealand Veterinary Journal, 64(1), 3-9.