Assessment of Common Hematologic Parameters and Novel Hematologic Ratios for Predicting Piroplasmosis Infection in Horses

Equine piroplasmosis (EP) is a tick-borne parasitic disease affecting equids with important health and economic impacts worldwide. Diagnosis is based on direct detection of the causative agents (Babesia caballi, Theileria equi, Theileria haneyi) in the bloodstream (PCR or blood smear) or an indirect demonstration of the immune response of the host against these parasites (serology). However, it is unknown if other simpler and faster techniques (such as hematology) could help clinicians to suspect or discard this disease. In this study we describe hematologic differences between non-infected and EP-infected horses and evaluate the ability of these hematologic parameters and ratios to predict EP status.

Equine piroplasmosis (EP) is a tick-borne disease affecting equids worldwide. Diagnosis is based on direct methods (blood smear or PCR) or indirect methods (serology); however, these techniques yield positive and negative results. Thus, an alternative, reliable, rapid, and cost-effective complementary tool, such as hematologic parameters and newly described hematologic ratios, could help in the EP diagnosis. This study describes the changes induced by piroplasmosis infection on hematologic parameters and ratios in horses. B. caballi PCR-positive horses exhibited anemia and thrombocytopenia, whereas T. equi PCR-positive horses showed anemia and leukocytosis. T. equi-seropositive horses had lower neutrophil and lymphocyte percentages than seronegative horses. Hematologic ratios displayed significant differences between negative and infected horses (mostly those infected by B. caballi). Most of the variations observed in these ratios were those previously linked to the worst prognosis or outcome in horses and humans. This study also evaluates the ability to predict the EP status of these hematologic parameters and ratios, with plateletrelated parameters showing a fair ability to predict a B. caballi PCR-positive result. While molecular methods remain the gold standard, complete hematology analysis and ratios could provide valuable complementary information to enhance the diagnostic accuracy of piroplasmosis in horses.