Ovine theileriosis is a hemoprotazoan infection transmitted by tick bites which cause severe economic loss. This study aimed to survey Theileria infection of sheep in different localities of Egypt (Cairo, Giza and Al Monofia) by using microscopic and molecular detection associated with clinicopathological and pathological investigations. A total of 152 sheep blood samples were selected from farms and veterinary clinics. Microscopic examination of blood smears revealed that the incidence of Theileria infection was 21.7% while the incidence was 36.8% using PCR assay (universal Theileria spp. Primer). The use of species-specific primers showed a result of 53.6% single infection; Theileria ovis, and 46.4% mixed infection; T. ovis and Theileria lestoquardi. According to the results of PCR, animals were divided into 3 groups: Theileria negative group, T. ovis group and mixed T. ovis and T. lestoquardi group. The examination of both infected groups revealed non-significant changes between them. The hemogram revealed significant macrocytic hypochromic anemia, leukopenia, neutropenia, lymphopenia, monocytopenia, eosinopenia and thrombocytopenia in Theileria infected groups compared with Theileria negative group. Biochemical analysis revealed significant hypoproteinemia, hypoalbuminemia, total and indirect hyperbilirubinemia with elevations of AST and GGT activities with increase in concentration of BUN and creatinine while no significant changes in A:G ratio values and direct bilirubin concentration in Theileria infected groups compared with Theileria negative group. The pathological investigation revealed lymphocytic depletion and necrosis with hemorrhages in lymph node and spleen.
