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These authors contributed equally.
INTRODUCTION
The order Piroplasmida (Phylum Apicomplexa) is mainly composed of the genera Babesia and Theileria (Levine et al. 1980; Criado et al. 2006). Classification of this order has been historically confined to parasite morphology, host cells in which schizogony occurs, levels of parasitaemia in the schizont and piroplasm stages, manifestation and pathology of clinical disease, as well as host and vector specificity (Barrnett, 1977; Uilenberg, 2006). By these criteria, the genus Theileria is distinguished by its ability to infect host leukocytes and to multiply by schizogony as part of its life cycle (Neitz, 1957; Uilenberg, 2006). Theileria species were first discovered based on clinical disease manifestation, linked with the observation of piroplasms in red blood cells and xenodiagnosis by tick transmission, as was the case for Theileria parva that caused Corridor disease and East Coast fever and T. annulata the causative agent of Tropical Theileriosis (Koch, 1903; Theiler, 1904; Dschunkowsky and Luhs, 1904; Lawrence, 1935). Observation of morphologically distinct piroplasm forms, with or without mild disease manifestation soon led to the discovery of more benign Theileria, such as T. mutans and T. velifera in cattle (Theiler, 1906; Uilenberg, 1964). New species were also discovered based on their presence in specific hosts, differential staining of blood smears and xeno-diagnosis, as in the case of T. taurotragi found in eland (Martin and Brocklesby, 1960; Brocklesby, 1962; Young et al. 1977).
Serology in the form of the indirect immuno-fluorescent antibody test (IFAT) was employed to distinguish species infecting the same host, but with different clinical manifestations, as is the case for T. parva and T. taurotragi (Young et al. 1977). The use of monoclonal antibodies and clonal cell culturing methods led to the discovery of antigenically distinct parasites from Cape buffalo (Syncerus caffer), thought to be T. parva (Conrad et al. 1987). Sequencing of the 18S ribosomal RNA (rRNA) gene showed, however, that T. sp. (buffalo) was a distinct entity from T. parva (Allsopp et al. 1993). Subsequently, the systematics of the Piroplasmida has been extensively studied by analysis of the 18S rRNA gene (Allsopp et al. 1994; Chae et al. 1999; Chansiri et al. 1999; Criado-Fornelio et al. 2004; Criado et...