[Soluble Babesia ovis antigen]

Dissolved antigen of plasma and of erythrocytic cytoplasma was obtained from 4 splenectomized sheep experimentally infected by Babesia ovis. Blood was taken in the stage of acute parasitemia with 23--25% parasite erythrocytes. The antigen was isolated by precipitating the plasma and the erythrocytic cytoplasma three times with an ammonium sulfate solution saturated 50 and 75%. The fraction obtained following dialysis was concentrated after McErlean's method. The specificity and activity of the isolated soluble antigen were proven by RAGP against serums of 6 weaned lamb groups: I group -- with 4 cm3 plasma, II group -- with 8 cm3 plasma, III group -- with 2 cm3 erythrocytic cytoplasma, IV group -- with live vaccine, V group -- with normal plasma and VI group -- normal weaned lambs. The same groups were used to assess the immunogenic properties of the dissolved antigen. Following provocation with a virulent B. ovis strain the lambs of group II proved as resistant as these immunized with live vaccine. The result was confirmed under production conditions -- not one of the 360 lambs immunized with 5 and 10 cm3 plasma became infected, while of the 250 control lambs 30 were infected. The conclusion is drawn that plasma in the stage of acute parasitemia can be used for immunoprophylaxis, but more supplementary studies are needed.