Unfortunately, the tick-borne cattle disease caused by Theileria orientalis has continued to spread through Virginia this year. We saw a peak of cases as fall calving commenced, with clinical signs ranging from down or weak animals to abortion storms. We have also seen poor appetite, decreased milk production, loss of libido in bulls, and anemia causing pale/yellow membranes. Most of our affected herds were in the central part of the state and we have yet to confirm a case east of the I-95 corridor. On a national level, cases have only been identified in Virginia and West Virginia, although the longhorn tick, which spreads the disease, has been identified in more than a dozen states.
Recognizing Theileria in Your Herd
Theileria shares some similarities with Anaplasmosis, another blood-borne disease of cattle that is spread by ticks. However, there are a few key differences. Theileria spreads far more efficiently than Anaplasmosis and affected herds often have 80‑90 percent positive animals. Theileria can cause disease in young stock. In contrast, young stock exposed to Anaplasmosis can become carriers, but develop immunity to clinical disease. Cattle with Anaplasmosis are often aggressive due to a lack of oxygen to the brain, while Theileria seems to cause a more generalized weakness. Abortions, still births, and weak calves are more commonly seen with Theileria than Anaplasmosis.
Best Practices for Treatment and Prevention
There are no approved treatments for this disease and infected animals appear to become carriers long-term. Affected herds generally have the most sickness in the first year and reach a state of stability in following years. We have had some success treating clinical animals with oxytetracycline and B vitamins. This treatment seems to reverse the signs of weakness in animals, but does not clear carriers. It is important to treat positive animals gently as stress or excitement can exacerbate clinical signs. Excellent nutrition is also important as animals recover from the disease.
Prevention is the best strategy when it comes to Theileria. Use effective fly and tick control throughout the year. Use individual needles when injecting cattle. Herds that feed tetracycline in the mineral to control the spread of Anaplasmosis may see a reduction in transmission of Theileria, but it does not eliminate transmission. Know the status of your herd and the status of new additions to the herd. The disease can be diagnosed by a blood test or post-mortem necropsy. This is a challenging disease that we will be battling in Virginia for years to come. Please don’t hesitate to contact us to work out the best strategy for your herd.
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