Causal agents of bovine theileriosis in southern Africa.

One pathogenic and 4 mild bovine Theileria strains from southern Africa, all transmitted by Rhipicephalus appendiculatus, were compared amongst themselves as well as to bovine and buffalo strains of the T. parva complex from eastern and southern Africa and to bovine strains of T. taurotragi from Tanzania considered to be derived from eland antelope. Criteria used were parasitological, clinical, serological and cross-immunity characters. The mild strains are similar to bovine T. taurotragi. Serological evidence suggested that T. taurotragi is also infective to sheep. The pathogenic strain belongs to the T. parva complex; the latter consists of a series of types with different behaviour ranging from the lawrencei-type (of buffalo) causing Corridor disease, through the bovis-type causing Rhodesian malignant theileriosis to the parva-type causing classical East Coat fever. Seven cattle-tick passages of a bovis-type strain did not result in transformation into a parva-type. Four species of bovine Theileriae are now known to occur in southern Africa: T. parva (lawrencei- and bovis-types) and T. taurotragi, both transmitted by R. appendiculatus, and T. mutans and T. velifera both with Amblyomma spp. as vectors.