Prevalence of Babesia bigemina and Theileria orientalis in Domestic Cattle (Bos taurus) Across the Three Geo-Climatic Zones of Sri Lanka.

Theileria orientalis and Babesia bigemina are hemoprotozoan parasites that adversely affect domestic cattle (Bos taurus) productivity and health worldwide. Rapid climatic changes in different geo-climatic zones observed over the past few years may have altered the distribution and transmission of tick-borne pathogens and vectors. Though these parasites are reported in Sri Lanka in surveillance records, there is a limited understanding of their current distribution pattern. The present study aimed to determine the prevalence and genetic characterization of B. bigemina and T. orientalis in cattle from three geo-climatic zones of Sri Lanka during the period from January 2025 to March 2026. Out of 384 samples collected from animals (wet, n = 124; dry, n = 208; and intermediate, n = 52 zones) in Sri Lanka, the overall prevalence of 60.2% for T. orientalis and 7.6% for B. bigemina was revealed using PCR-based detection methods. The highest prevalence of T. orientalis was observed in the wet zone (86.3%), while the highest prevalence of B. bigemina was 17.3% in the intermediate zone. Co-infections were detected in 5.7% of cattle across all three zones. These results indicate the dominance of T. orientalis compared with B. bigemina in cattle in Sri Lanka. The observation of co-infections highlights the importance of vector control against vector-borne diseases in Sri Lanka.