ABSTRACT
A pathogenic Theileria stock was isolated from control cattle during an East Coast Fever (ECF) field immunization trial at Kasoba near Karonga town in northern Malawi. A stabilate of this stock caused severe fevers and prolonged parasitosis in Theileria parva naive cattle, resulting in the death of 5 out of 12 cattle despite treatment. In contrast, this parasite stock caused mild to moderate reactions in 17 cattle immunized with the trivalent T. parva stabilate except in 3 animals which developed severe reactions, and one of them died. Another time, cattle immunized with buffalo-derived Theileria parva (Serengeti transformed) resisted a potentially fatal challenge, with only mild to moderate reactions being recorded. The parasite stock was morphologically and serologically indistinguishable from Theileria parva (Muguga); it was virulent and could cause mortality, particularly in T. parva naive cattle. The parasite stock was designated Theileria parva (Kasoba).
