06/24/2026
While speaking to a client briefly today and thinking of the many other conversations I have had, I decided that a quick overview of Theileria in cattle is warranted.
Theileria orientalis is a tick-borne disease transmitted by the Asian longhorn tick pictured below. The disease appears to have entered this area 3-5 years ago. The organism enters the body and begins infection in the bloodstream, infecting white and red blood cells. Symptoms have been known to vary greatly. It can present similarly to Anaplasmosis, which we have dealt with for years. An adult animal with weakness, possibly unable to stand, and eventually death. But we have also found that it can cause a compromised immune system, which allows animals to be more susceptible to pneumonia, abscesses, and other diseases that usually would not be that severe. In these cases, it seems that the animals cannot recover from common illnesses. This also includes calves, whereas anaplasmosis only affects adults clinically.
Unfortunately, there is no approved treatment for Theileria in the United States, but it is essential to treat any other symptoms seen, such as antibiotics for pneumonia, abscesses, etc. Because the tick is the primary vector, it is crucial to be more vigilant in tick prevention. Also, consider not putting the herd in heavily wooded areas during peak tick season. As the tick is the primary vector, it can also be transmitted by needles when vaccinating and treating animals, so it is good practice to switch needles between animals. Please do not hesitate to reach out if you have any questions. (573) 477-3321
