Molecular phylogenetic study of Theileria sp. (Thung Song) based on the thymidylate synthetase gene.

Theileria type Thung Song is an indigenous hemoparasite of dairy cattle from the south of Thailand. It has previously been classified using the analysis of a comparative set of small subunit ribosomal RNA nucleotide sequences. However, the classification of this parasite is still questionable since the Theileria type Thung Song was located as the intermediate parasite between pathogenic and benign groups. We use the thymidylate synthetase gene (TS) as an alternative for the rapid molecular phylogenetic tree construction of benign Theileria type Thung Song, Theileria sergenti and Theileria buffeli with Babesia bovis as an out-group. The partial nucleotide sequences were determined using PCR, cloning and dideoxy sequencing. The TS nucleotide sequence data were aligned and analyzed by distance and maximum likelihood methods to construct the phylogenetic trees. Bootstrap analysis was used to test the strength of the different phylogenetic reconstructions. All tree-building methods gave similar results. This study shows that T. sergenti and T. buffeli are closely related whereas Theileria type Thung Song is more distantly related.