The aim of the study was to investigate the clinical and hematological findings in crossbred cattle and water buffaloes naturally infected with Theileria annulata with special reference to the clinical picture of tropical theileriosis in Egyptian buffaloes. A total 50 field cases of cattle and buffaloes delivered to Veterinary Medicine Hospital, Zagazig University during the period from March to
June 2008 and were investigated clinically and laboratory at arrival. Forty four (88%) cattle and buffaloes were naturally infected with T. annulata and showed typical signs of infection: fever, enlargement of the superficial lymph nodes, severe lacrimation, bilateral conjunctivitis, photophobia, corneal opacity and respiratory manifestations. Six animals (12%) showed no clinical
signs and were free from external, internal and blood parasites. It was clear that the severity of clinical signs in infected buffaloes was more prominent than in infected cattle with persistence of some lesions after recovery as corneal opacity and pulmonary lesions. Hematological analysis revealed a significant decrease in RBCS count, PCV%, hemoglobin amount and WBCs in the infected animals comparing to the healthy ones (P≤0.05). In conclusion T. annulata infection is
associated with impairment and alteration of blood parameters in both cattle and water buffaloes. Theileriosis in water buffaloes might cause irreversible ocular changes that could lead to complete blindness. Data obtained in this study might put the basis for the subsequent studies under natural
and experimental field conditions.