Equine Piroplasmosis: Clinical Symptoms, Clinical Pathology, Immunity and Treatment

Introduction
Equine piroplasmosis (EP) is a tick-borne protozoal disease reportable to the World Organization for Animal Health (OIE). The causative agents are Babesia caballi and Babesia (Theileria) equi. Horses infected with B. equi remain carriers for life, and serve as reservoirs for transmission to naïve horses. It is estimated that 90% of the world’s horses are exposed to 2-4) EP. In these endemic regions, exposure occurs within the first year of life with case fatality rates of 5-10% in naïve horses while this rate can exceed 50% when naïve horses are introduced in endemic regions

Transmission
Both EP agents can be transmitted by same tick vectors leading to frequent co-infection. For B. caballi, ticks serve as a reservoir where the organism can persist through several generations. For B. equi horses are the primary reservoir. Iatrogenic means can also be factors for transmission.

Clinical signs and differential diagnoses
Clinical signs of EP are similar for both agents infection. Typical clinical signs of acute EP can include fever, anorexia, anemia, icterus, congested mucous membranes, tachypnea and tachycardia, sweating, limb and supraorbital edema. In severe cases, hemoglobinuria and bilirubinuria are present as well as a variety of atypical presentations due to organ damage and dysfunction. Death may occur in severe cases. The clinical signs of EP are consistent with other diseases including equine infectious anemia (EIA), purpura hemorrhagica, idiopathic immune-mediated anemia, and intoxications.

Clinical pathology
While not specific of EP, infected horses usually show reduced red blood cell count, platelet count and hemoglobin concentration as well as elevated bilirubin concentration and prolonged clotting time. Variations of the white blood cells lines can also occur at varying degrees. In chronic forms only mild anemia is present with no change in serum bilirubin concentration.  [...]