The effect of treatment with imidocarb diproprionate on the course of Babesia divergens infections in splenectomized calves, and on their subsequent immunity to homologous challenge

Abstract The drug imidocarb diproprionate (IMDP) was injected intramuscularly into groups of splenectomized calves at 2·4 mg per kg body weight at various times before and during their reactions to syringe-passaged Babesia divergens infections. When the drug was given 1 or 2 weeks before infection it had a prophylactic effect, inducing appreciably milder B. divergens reactions in the calves and complete immunity to challenge. When it was given simultaneously with the parasites, the development of the infection was almost completely suppressed and no immunity to challenge developed. If B. divergens infections were allowed to develop for 7, 14 or 21 days before treatment, the infections were sterilized by the drug but the animals retained an immunity to challenge. The strength of this immunity increased with the length of time that the parasites had been allowed to exist before treatment. These results demonstrate that IMDP is an effective drug against B. divergens infections but suggest that blanket-treatment of all animals in a herd at the first sign of the disease may not invariably prevent further redwater cases.