The Immunogenicity of Irradiated Theileria Parva( Katete) Sporozoites in the Immunisation of Cattle against Malignant Theileriosis
The effect of irradiation on the Katete stock of Theileria parva sporozoites either directly (stabilate form) or indirectly (in their tick vectors) was compared to the 'infection and treatment' method of immunisation of cattle against malignant theileriosis. Fifteen steers were randomly divided into five groups using a computerised random number generator. The first group comprising three steers was immunised with T. parva sporozoites harvested from Rhipicephalus appendiculatus ticks and then irradiated at 8.4 krads using the Cobalt source. In the second group, four steers were immunised with T. parva sporozoites irradiated at 20 krads in their R. appendiculatus tick vectors. The third and fourth groups consisting of three steers each were immunised with non-irradiated T. parva sporozoites. In addition, the fourth group was also treated with tetracycline (infection and treatment). The fifth group (control) with two steers was introduced during the challenge of immunised animals and was treated with lethal doses of T. parva stabilates only. The steers in all experimental groups, except the control, resisted lethal challenge with homologous T. parva stabilates. Mild and moderate reactions were observed in the group of steers immunised with stabilates produced from T. parva sporozoites irradiated in their tick vectors (group two) and non-irradiated stabilates only (group three), respectively. Steers in the control group died from East Coast fever. The best results were obtained from the groups of steers immunised with directly irradiated T. parva sporozoites and non-irradiated stabilates with concurrent tetracycline therapy. There was no statistically significant difference(P>0.05) between the infection and treatment method of immunisation and that of directly irradiated stabilates. Estimates of costs showed that farmers would save between $0.39 (calf) and $2.39 (adult) per animal if they used irradiated stabilate instead of tetracycline in the immunisation.
Malignant Theileriosis , Cattle Vaccination