Molecular phylogenetic studies on Theileria parasites based on small subunit ribosomal RNA gene sequences

Classification of Theileria parasites of south-east Asian countries is stil l ambiguous due to the lack of basic studies, especially their molecular ge netic information. In this study, we included 6 known species and 14 unclas sified Theileria parasite isolates: Theileria annulata, Theileria parva, Th eileria taurotragi, Theileria sergenti, Theileria buffeli, Theileria types Sable, Theileria types A, B,B1, B2, C, D, E, F, G, G1, Theileria type Medan (Indonesia), Theileria type Ipoh (Malaysia) and Theileria type Thong Song (Thailand). Small subunit ribosomal RNA (srRNA) nucleotide sequence data we re collected by PCR, cloning and dideoxy sequencing. The srRNA nucleotide s equences were aligned and analyzed by distance methods, maximum parsimony a lgorithms and maximum likelihood methods to construct phylogenetic trees. B ootstrap analysis was used to test the strength of the different phylogenet ic reconstructions. The data indicated that all of the tree-building method s gave very similar results. This study identified two groups of Theileria, the pathogenic and benign groups, which are strongly supported by bootstra p analysis. The analysis also indicated that three subgroups (A, B and C) w ere generated within the benign Theileria group whereas the classification of Theileria type D and Thong Song is questionable. However, more basic inf ormation such as life cycle differences, vectors, modes of transmission, vi rulent and genetic/sexual compatability is essential for clearer taxonomic definition of the benign Theileria parasites. (C) 1999 Elsevier Science B.V . All rights reserved.