Summary

Equine piroplasmosis is a tick‑borne blood disease affecting horses, donkeys, mules, and zebras, caused by Babesia caballi and Theileria equi. While uncommon in the United States, it is endemic in many tropical and subtropical regions and is a concern for international horse movement. The parasites infect red blood cells, leading to anemia and systemic illness. Transmission occurs mainly through tick bites but can also occur through contaminated needles, blood transfusions, or from mare to fetus. Clinical signs vary and may include fever, anemia, jaundice, weakness, sweating, neurologic deficits, weight loss, edema, or sudden death, while some horses show minimal signs or reduced performance. T. equi infections are often lifelong, leaving horses as carriers. Diagnosis can be difficult, there is no vaccine, and treatment may reduce symptoms but often does not eliminate infection. Prevention relies on testing, quarantine, tick control, biosecurity, and mandatory reporting.