Effect of ionizing radiation on the virulence and the immunogenic properties of Babesia ovis

The effect was followed up of ionizing radiation of 20, 25, 30, 32, 35, 40 and 50 krad on the virulence and the immunigenic properties of B.ovis. The experiments were carried out with 22 sheep (20 test and 2 donor) according to the rate of treatment into 7 test groups with a total of 17 animals, and 1 control with 3 sheep. One month after infection with irradiated blood reinfection was carried out of 8 animals (of different groups) that had recovered, using virulent untrated blood. The titer of the antibodies in the remaining sheep was followed up by means of the complement fixation test. It was found that irradiation at 20 - 25 krad lowered the virulence of the Babesia organisms, but these could provoke the disease in an acute form and cause death. The animals that survived after being infected with the indicated doses developed a comparatively good immunity. It is considered that the most appropriate dose of irradiation is 30 krad. 32 and 35 krad do not kill Babesiae; the parasites thus irradiated, however, cannot protect the animals ar reinfection. It has been found that Babesiae irradiated at the rates of 40 and 450 krad do not cause an infection process, and at reinfection the animals respond almost in the same way as the controls. (author)