author(s)
R Edith, TJ Harikrishnan, S Gomathinayagam, P Kumarasamy and TMA Senthilkumar

abstract
Theileria annulata is a haemoprotozoan parasite which causes Bovine Tropical Theileriosis in cattle. It is an important tick borne disease of tropical and subtropical countries. Conventional diagnostic methods are unreliable to diagnose the subclinical or carrier status of the disease. Polymerase chain reaction (PCR) assay based diagnosis using different target genes like 18SrRNA has been developed. In this study, an extra chromosomal DNA, cytochrome b gene has been utilized to screen T. annulata infection in cattle from two different agro climatic zones of Tamil Nadu. Significantly high level (p>0.01) of T. annulata infection (25.66%) has been detected using cytochrome b gene based PCR whereas only 2.88% prevalence has been detected by conventional blood smear examination. North eastern agro climatic zone has shown a significantly (p>0.01) higher prevalence of T. annulata (26.95%) by cytochrome b PCR than North western zone (22.96%). Cattle aged more than six years have shown a significantly (p>0.01) higher prevalence (31.75%) than the cattle aged less than three years (11.11%). Present study clearly indicates that cytochrome b based PCR is a better target for epizootiological screening of bovine tropical theileriosis.