Theileria annulata is common in tropical and subtropical regions especially in Iran and causes great economic losses in cattle industry. In Iran the epidemiological aspects of bovine theileriosis in different breeds of cattle is poorly understood. The aim of present study is comparison of the number of T. annulata carriers in the two major cattle breeds (Holstein-Friesian and Sistani) in Sistan of Iran by giemsa and polymerase chain reaction (PCR) methods. During winter 2013, 160 native cattle, from the two major breeds in Sistan, with the mean age of more than one year and without typical clinical symptoms of theileriosis were selected. At first, a thin layer smear was held from their ear sublime vein blood for Giemsa staining method. In order to do PCR assay, jugular vein blood sample of each cow was taken. The PCR employs primers specific for the 721-bp gene fragment encoding the 30-kDa major merozoite surface antigen of T. annulata. By PCR method, 38 (47.5 %) Holstein blood samples and 22 (27.5 %) Sistani blood samples had DNA of T. annulata and considered positive (The correlation was significant at values of P < 0.05). By checking 160 blood smears with light microscope and lens × 100, only 10 samples (6.25 %) were positive for T. annulata. Statistical comparison between PCR and smear method showed that the PCR method is more sensitive and accurate in comparison to Giemsa staining method to diagnose the asymptomatic carriers of T. annulata.
Keywords: Asymptomatic carriers; Holstein; PCR; Sistani; Theileria annulata.