A study of the systematics of Theileria spp. based upon small-subunit ribosomal RNA gene sequences

The systematics of benign and moderately pathogenic Theileria isolates from cattle and deer originating from different geographic regions was undertak en by small-subunit ribosomal RNA (SSU rRNA) gene nucleotide-sequence analy sis. A maximum-likelihood phylogenetic tree constructed from these sequence s resulted in two major divisions, each with a common ancestor. One major d ivision branches into four relatively divergent groups, including (1) bovin e Theileria sp. Type D (USA and Korea), (2) T. mutans Intona and Theileria sp. MSD (Africa), (3) T. cervi (USA), and (4) well-characterized pathogenic Theileria spp. (Africa). The other major division branches into two groups : (1) T. buffeli Warwick and T. buffeli Marula and (2) a second branch of c losely related isolates with SSU rRNA gene Types B, B1, C, E, and H. Putati ve geographically associated diversity was noted only in the Korean bovine Theileria spp. with SSU rRNA gene types C and H and in African T. mutans In tona and Theileria sp. MSD. The current results show that the United States bovine Theileria isolates are not T. mutans because they have T. buffeli M arula (Type A) and/or Type D (species undesignated) SSU rRNA gene sequences . The taxonomic separation of T. buffeli Warwick from African T. mutans is confirmed in this study.