The present study was aimed to investigate some oxidative stress indices in the erythrocytes from sheep naturally infected with theileriosis. Thirty adult fat-tailed sheep suffering from theileriosis were selected on the basis of clinical examination and positive peripheral blood smears and twenty clinically healthy animals without parasitaemia (according to the blood smears) served as controls. The oxidative stress indices including enzymatic activities of superoxide dismutase, glutathione peroxidase and catalase, glutathione and malondialdehyde were measured in erythrocyte haemolysate. The activities of antioxidant enzymes including superoxide dismutase and glutathione peroxidase were considerably decreased in infected sheep compared to controls, although the decrease was only significant (P<0.05) for superoxide dismutase activity. By contrast, catalase activity was non-significantly higher in the infected group compared to control group. Malondialdehyde concentration was significantly enhanced in erythrocytes of infected group, whereas glutathione level was significantly reduced in infected group in comparison to controls. Disturbed antioxidant mechanisms of erythrocytes in infected group, accompanied by a significant rise in erythrocytic lipid peroxidation, implied that the oxidative stress may have a pathophysiological role in ovine theileriosis.

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