Use of serological response to evaluate heartwater immunization of cattle.

Frozen blood vaccine containing the Ball 3 strain of Cowdria ruminantium is prepared by an FAO/DANIDA Project in Malawi for the immunization of improved dairy cattle against heartwater. The immunogenicity of vaccine batches for cattle has been quantified and different regimens for immunization have been evaluated using indirect immunofluorescence to assess antibody responses. Infected endothelial cells grown in culture are used as antigen. The proportion of animals responding serologically has varied between different batches of vaccine tested in homogeneous cattle populations at the same time, presumably reflecting differences in immunogenicity of batches. The proportion of animals in a homogeneous population responding serologically to the same vaccine batch administered under different regimens has also varied. Indirect immunofluorescence testing has proved to be a useful method for assessing the immune response of cattle to immunization and has been adopted as a routine quality control procedure for heartwater vaccine production in Malawi.