Dr. Kerry Barling: New Tick-Borne Cattle Disease: What to Know

Dr. Kerry Barling Deputy State Veterinarian

In August, just prior to the Kentucky State Fair, the Kentucky Department of Agriculture announced two cases of a new cattle disease detected in beef herds in Fleming and Hart counties. Each case involved a beef breed bull. The disease was fatal in both cases, with no relationship between the herds. Many questions exist about this disease, which is caused by a microscopic parasite, Theileria orientalis Ikeda, carried by the Asian Longhorned Tick (ALT). Theileria can be transferred to cattle from the tick following a blood meal. Theileria infects blood cells in cattle causing fever, severe anemia, abortions, stillbirths, and occasional deaths. An affected cow will have pale or yellow mucous membranes, rapid respiration, and pulse rates. Infected bulls may have lowered libido, and infected cows may have decreased milk production. The disease can be confused with pneumonia because of the respiratory distress. Theileria can also be confused with anaplasmosis, another cause of anemia in cattle. Currently, there are no vaccines or effective treatments available for Theileria infections. Cattle that survive acute infections of Theileria are known to become persistently infected and serve as a reservoir of infection to other cattle. The ALT was discovered in the U.S. in 2017 in New Jersey, and Theileria was first found in cattle that same year in Virginia. Since then, ALTs have been found in at least 17 states, and Theileria has been found in cattle from at least seven states. It appears Kentucky is on the advancing westward edge of tick/Theileria spread. In Kentucky, the ALT has been identified in Boone, Breathitt, Floyd, Madison, Martin, Metcalfe, and Perry counties. It is likely both the tick and Theileria are present and undetected in additional Kentucky counties. The ALT has been found to attach to livestock, wildlife, birds, dogs, cats, and humans. Something important to consider is that Theileria only causes disease in cattle through blood-toblood transmission. Infected cattle pose no risk to humans through direct contact, or consumption of its meat or milk, provided the meat is cooked to a proper temperature and the milk has been pasteurized. The disease is spread in and between cow herds from infected ALTs, injections with contaminated needles, use of contaminated surgical tools (dehorners, castration knives, etc.), and biting insects. Diagnosis of Theileria infections in cattle can be made by submission of blood samples and/or body tissues (spleen) to veterinary disease diagnostic laboratories. While disease responsible from Theileria infections is known to occur only in cattle, the ALT can carry other infectious agents that are responsible for disease in animals other than cattle, including humans.

Treatment of acutely ill cattle primarily involves supportive care; however, blood transfusions may be beneficial in some cases. The most effective means of reducing the risk for Theileria infections in cattle is through tick control, single-use needles, and management of persistently infected cattle. Tick control measures include keeping pastures mowed and cattle restricted from wooded areas. Regular inspection of cattle for ticks and use of ear tags, pour-ons, or back rubs that contain an acaricide are helpful. Working with your veterinarian and/or an entomologist can assist with tick control and identification through a program with the University of Kentucky Tick Laboratory. The Office of State Veterinarian at the Kentucky Department of Agriculture (KDA) has created two alert fliers, “Theileria Orientalis Ikeda in Cattle” and “Theileria Orientalis Ikeda Info.” Both fliers can be found on the KDA website at kyagr. com/statevet by scrolling down to a list of “Forms & Documents.” Further questions can be directed to KDA at statevet@ky.gov or (502) 573-0282.