Haematological Changes and Hyperbilirubinaemia in Sheep Naturally Infected with Babesia ovis in an Enzootic Focus

Malignant ovine babesiosis is a seasonal tick-borne disease associated with anaemia and potentially high mortality. The aim of this study was to characterise haematological changes and total bilirubin concentrations in naturally infected sheep originating from an enzootic focus of Rudo in Bosnia and Herzegovina. Twenty PCR-confirmed sheep showing clinical signs compatible with malignant ovine babesiosis and ten clinically healthy, PCR-negative control sheep were examined. Blood samples were collected from the jugular vein into EDTA tubes, and haematological parameters were determined using an automated analyser, while total bilirubin was measured by reflectometry. Parasitaemia was assessed microscopically on Giemsa-stained blood smears using a semi-quantitative scale. All infected animals were assigned to the lowest parasitaemia category (<1%). The infected sheep had significantly lower erythrocyte count, haemoglobin concentration and haematocrit than controls, while the mean corpuscular volume did not differ significantly between the groups. The most prominent finding was severe thrombocytopenia, with a mean platelet count of 91.95 × 10⁹/L compared with 426.40 × 10⁹/L in controls. The total bilirubin concentration was also significantly higher in the infected sheep. The marked thrombocytopenia observed despite low microscopically detected parasitaemia suggests that mechanisms other than parasite burden alone may contribute to platelet depletion, although the underlying mechanism cannot be established from the present data. The findings provide laboratory data from naturally occurring malignant ovine babesiosis in an enzootic focus in Bosnia and Herzegovina and highlight severe thrombocytopenia and hyperbilirubinaemia as prominent findings.