Babesia divergens: the immunisation of splenectomised calves during irradiated piroplasms.

Groups of three splenectomised calves were inoculated with 1 . 2 x 10(10) Babesia divergens-infected erythrocytes irradiated at 24, 28, 32, 36 and 40 kilorads. Control calves were inoculated with 1 . 2 x 10(7) or 1 . 2 x 10(4) non-irradiated parasites. While control animals all experienced severe reactions, animals receiving blood irradiated at 24, 28 and 32 kilorads had mild reactions and were solidly immune to an homologous challenge of 1 . 1 x 10(4) Babesia-infected erythrocytes. Animals receiving parasites irradiated at 36 and 40 kilorads had limited ability to resist the challenge.