Molecular Characterization and Phylogenetic Insights into Theileria annulata Affecting Cattle in Western Uttar Pradesh, India

Abstract Theileriosis is a significant protozoan disease in cattle that is transmitted by ticks and poses a major health concern for bovine populations. With rising case numbers and strain-specific clinical variability, the genetic characterization of Theileria spp. in different geographical regions has become crucial. However, limited molecular data are available on the genetic diversity and identity matrix analysis of Theileria spp. in cattle. This study aimed to genetically evaluate Theileria spp. isolates affecting cattle in Western parts of Uttar Pradesh, India. In the present investigation, one hundred blood samples were collected from bovines exhibiting clinical signs consistent with Theileria infection in the study. Initial screening was conducted using Giemsa-stained thin blood smears, followed by molecular validation confirmation using polymerase chain reaction (PCR) targeting the 18S ribosomal RNA (rRNA) gene. Genetic analyses were performed using the MEGA-X software. Microscopic examination identified Theileria spp. in 17% of the samples, whereas PCR detected the parasite in 53% of the examined samples. Following 18S rRNA gene sequencing and bioinformatic analysis, all field isolates were found to be clustered into a single clade, showing 95.96–98.49% sequence homology with Theileria annulata. These findings highlightsthe significance of improving molecular surveillance and genetic profiling of Theileria spp. across diverse regions to better understand their epidemiology and inform control strategies for bovine theileriosis in India.