Piroplasmosis in Italian Standardbred Horses: 15 Years of Surveillance Data

This study aimed to document the prevalence of chronic equine piroplasmosis (EP) in poorly performing Standardbred racehorses and to explore associations between the disease and sex, age, and hematological parameters. Blood was collected between 2004 and 2018; blood cell counts were performed using a cell counter analyzer, biochemical parameters using a photometer, and serum proteins using agarose gel electrophoresis. Blood smears were prepared, colored with a modified Giemsa, and an experienced technician identified the presence of protozoa. The horses were categorized into piroplasmosis positive (PP) and piroplasmosis negative (PN). The studied population included 520 horses (142 female, 27.6%; CI, 23.8%-31.7%), with a median age of 4 (interquartile range, 3-8) years. The prevalence of EP was 9.3% (CI: 6.9%-12.1%). There was no association between the infectious status and signalment. In poorly performing Italian Standardbreds, chronic piroplasmosis caused mild normocytic, normochromic anemia, hyperbilirubinemia, thrombocytopenia, and hypergammaglobulinemia, as reported in literature. However, our findings suggests that blood analysis needs to be interpreted with caution as there were cases with overlap between parameters in PP and PN horses, and normal ranges. Hence, in cases of poorly performing Standardbreds living or recently moving into an EP-endemic region, blood cytology should be performed as a first step in differential diagnosis procedures to exclude chronic EP as one possible cause for poor performance. Further diagnostic tests (i.e., PCR, ELISA) are also recommended because correct diagnosis is vital to ensure the criteria of "lack of disease" in the welfare principle of good health.