Equine Piroplasmosis Study Guide

Overview and Clinical Importance

Equine piroplasmosis (EP) is a tick-borne, hemoprotozoan disease of equids caused by the intraerythrocytic apicomplexan parasites Theileria equi and Babesia caballi. A third species, Theileria haneyi, has recently been identified but appears to have lower pathogenicity. EP is a WOAH (formerly OIE) reportable disease that affects horses, donkeys, mules, and zebras worldwide.

This disease has significant economic impact due to treatment costs, restrictions on international horse movement, reduced performance in sport horses, and potential mortality rates of 5-10% in endemic areas and up to 50% in naive animals imported to endemic regions.

Etiology and Causative Agents

Equine piroplasmosis is caused by two primary hemoprotozoan parasites within the phylum Apicomplexa and order Piroplasmida. The term "piroplasmosis" derives from the pear-shaped (pyriform) appearance of the intraerythrocytic merozoite stage.