Discovery of a new Theileria sp. closely related to Theileria annulata in cattle from Sri Lanka.

Theileria annulata is a haemoprotozoan parasite that causes a cancer-like illness known as tropical theileriosis in cattle. In the course of analyzing the genetic diversity of T. annulata in Sri Lanka, we observed that merozoite-piroplasm surface antigen (tams1) and surface protein (tasp)-like gene sequences obtained from bovine blood DNA samples, which were PCR-positive for T. annulata, were conserved but shared low identity with T. annulata GenBank sequences. Moreover, the 18S rRNA sequences from the Sri Lankan samples contained ten unique single-nucleotide polymorphisms compared with all known T. annulata sequences. The cytochrome b (cob) gene sequences isolated from the Sri Lankan samples were highly conserved and shared low identity scores with similarly conserved T. annulata sequences from GenBank. Phylogenetic analysis showed that the Sri Lankan tams1-like, tasp-like, 18S rRNA, and cob sequences clustered together and formed sister clades to the common ancestors of all known T. annulata and Theileria lestoquardi sequences. These findings demonstrated that the Sri Lankan cattle were not infected with T. annulata but with a new Theileria sp. (designated as Theileria sp. Yokoyama) closely related to T. annulata.