CHALLENGE OF THEILERIA-PARVA (BOLENI) IMMUNIZED CATTLE WITH SELECTED EAST-AFRICAN THEILERIA STOCKS

Theileria parva (Boleni) stock from Zimbabwe was used to immunise 24 s usceptible Friesian calves by infection and treatment with oxytetracyc line. Twenty-eight clays after immunisation the animals in groups of 6 plus 2 susceptible controls were subjected to challenge: 3 groups wit h heterologous stocks and one group with the immunising stock. Theiler ia parva (Boleni) gave good protection against homologous challenge, t he T. parva (Muguga, Kenya) and buffalo-derived T. parva (Serengeti tr ansformed Tanzania) parasite stocks. It did not protect against the T. parva (Kasoba, Malawi) stock and 3 out of 6 immunised cattle died and the remaining 3 had to be treated with parvaquone. In a second experi ment, the 6 T. parva (Boleni) immunised animals which had received hom ologous challenge, together with rite 2 controls which had recovered w ithout treatment from T. parva (Boleni) infection, were challenged wit h the T. parva (Kasoba) stock. Four out of 6 of the immunised animals resisted the challenge with mild to moderate reactions. The other 2 an imals had severe reactions and one died. The 2 control animals which r ecovered from T. parva (Boleni) infection resisted the T. parva (Kasob a) challenge and both had mild reactions. It is suggested that oxytetr acycline used in the first experiment may have interfered with the exp ression of the full protective capacity against the virulent T. parva (Kasoba) stock. Further studies on the use of the T. parva (Boleni) st ock without oxytetracycline treatment could identify a more broadly im munising effect and a more economical vaccination method.