Equine piroplasmosis, caused by Babesia equi and Theileria equi transmitted by ticks, causes fever, anaemia, and severe systemic illness with significant welfare implications for sport horses.
Piroplasmosis causes acute severe suffering through haemolytic anaemia — the immune-mediated destruction of red blood cells causing jaundice, weakness, and in severe cases cardiovascular compromise. Affected horses show marked depression, reluctance to move, and pale or icteric (yellow) mucous membranes reflecting severe anaemia. Horses that survive become lifelong carriers of Theileria equi, facing restrictions on international movement and potential reactivation during stress or illness. The welfare priority in endemic areas is rigorous tick control and prompt treatment recognition. Horses imported to non-endemic countries require accurate serological testing to prevent introduction of the disease.