Theileria orientalis in Oklahoma

By Barry Whitworth, DVM

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

In the United States, the first case of theileriosis was identified in Virginia in August 2017. These cattle exhibited clinical signs of weakness and anemia. An initial diagnosis of anaplasmosis was made. Blood samples from the animals were tested for Anaplasma, Babesia, and Leptospira. Test results were negative for all three; however, a blood protozoan was detected. This organism was identified as T. orientalis genotype Ikeda. Since this initial herd outbreak, the organism has been detected in several states.

Cattle infected with and showing illness from T. orientalis genotype Ikeda may exhibit clinical signs such as 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. Upon examination, the gums, eyes, or vaginal mucosa may appear pale (white) or yellow in color. Reproductive losses, including stillbirths and late-term abortions, may occur, along with a reduction 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, weight loss, anemia, poor performance, and sudden death have been reported.

Because Anaplasma marginale and T. orientalis genotype Ikeda produce similar clinical signs, distinguishing between the two can be challenging.

One notable difference is that clinical signs are more commonly observed in young cattle infected with T. orientalis, whereas this is less common in cattle infected with A. marginale. Additionally, cattle with anaplasmosis often display aggression, whereas those with T. orientalis genotype Ikeda typically do not. A laboratory test is required to definitively differentiate between the two diseases.

Haemaphysalis longicornis has been identified as a possible vector of T. orientalis genotype Ikeda. In 2017, the United States Department of Agriculture’s (USDA) National Veterinary Services Laboratories (NSVL) confirmed the presence of H. longicornis, commonly referred to as the Asian longhorned tick (ALT) or bush tick. In efforts 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. There is also some evidence suggesting additional insect vectors may 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 congregate, such as along deer trails. Producers seeking more information about the ALT can visit the USDA website at: https://www.aphis.usda. gov/livestock-poultry-disease/ cattle/ticks/asian-longhorned.

In other countries, treatments have been developed for T. orientalis. Unfortunately, no approved treatments are currently available in the United States, and no vaccines exist for this disease. The best defense is prevention: purchasing cattle free of the organism, avoiding blood transfer between animals, and implementing effective tick control measures. Producers should purchase cattle from reputable sources. Instruments should be cleaned between animals during procedures such as castration or dehorning, and needles should always be changed between animals. External parasites must be controlled using appropriate insecticide treatments. In addition to insecticides, pasture management strategies—such as rotation to avoid wooded or brushy areas where ticks thrive—are important. Patch burning may also help reduce tick populations.

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

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

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