Insight into oriental theileriosis: Indian perspective.

Theileria orientalis, an emerging haemoprotozoa, primarily targets large ruminants, especially cattle. Being a globally distributed haemoprotozoa, it causes oriental theileriosis, which is transmitted by the tick vector Haemaphysalis longicornis. In tropical countries, such as India, Rhipicephalus microplus (Asian Blue tick) is another potential vector for disease transmission. Unlike T. parva and T. annulata, schizonts of T. orientalis are non-lymphoproliferative in nature and the main pathogenic effect is contributed by the piroplasms destroying erythrocytes, resulting in anemia. The T. orientalis complex comprises multiple genotypes, with Ikeda (Type 2) and Chitose (Type 1) being the most virulent. In recent years, various clinical outbreaks of oriental theileriosis with pathogenic genotypes have been recorded worldwide, often fatally affecting naïve cattle, calves and pregnant animals. In India, the disease is emerging as a significant threat to livestock health and productivity, particularly in regions with high tick infestation and suboptimal veterinary infrastructure. Molecular epidemiological studies from various Indian states have confirmed the presence of pathogenic genotypes, including Ikeda and Chitose types, often associated with clinical disease and economic losses. Prompt and accurate diagnosis using both conventional and molecular methods is essential to rule other haemoprotozoan infections in cases where symptoms overlap. Enhanced awareness of the risks associated with the parasite is essential for facilitating the implementation of management practices aimed at mitigating its impact. This review focuses on the classification, prevalence, life cycle, pathogenesis, diagnosis and prophylaxis of T. orientalis focusing on reports pertaining to India.