Serological differentiation between infected and vaccinated cattle by using purified soluble antigens from Brucella abortus in a hemagglutination system.

Serological tests used in current brucellosis eradication schemes, such as bacterial tube agglutination, do not readily distinguish between infected animals and those immunized with strain 19 or 45/20 Brucella abortus vaccines. In this study, sera from naturally infected cattle were used to identify serologically important antigens in extracts of virulent B. abortus by gel diffusion techniques. Antisera from rabbits hyperimmunized with selected precipitation lines were used for purification by affinity chromatography of two precipitating and one non-precipitating antigen from crude bacterial extracts. A passive hemagglutination test using these antigens was developed. A number of characterized bovine sera were screened by passive hemagglutination and conventional bacterial tube agglutination test. A considerable improvement in discrimination between sera from infected and vaccinated cattle was obtained with the hemagglutination test compared with bacterial tube agglutination.