Effect of imidocarb dipropionate prophylaxis on the infectivity and immunogenicity of a Babesia bovis vaccine in cattle.

Imidocarb dipropionate (IDP), a potent prophylactic drug against Babesia bovis infections in cattle, was tested for its effect on the infectivity and immunogenicity of a live B. bovis vaccine marketed in Australia. At the recommended prophylactic dose rate of 3 mg/kg, IDP suppressed infectivity of the vaccine for at least 6 weeks. The vaccine infected all cattle inoculated either 8 weeks after treatment with 3 mg/kg, or 4 weeks after treatment with the recommended therapeutic dose of 1.2 mg/kg. These infections were, however, partially suppressed and the level of immunity to a subsequent heterologous virulent challenge was reduced. Cattle that failed to become infected after vaccination were fully susceptible to the challenge. It is concluded that where B. bovis vaccination is contemplated, prophylactic use of IDP should be avoided.