THE EFFECTS OF ANTIGENIC-COMPETITION ON THE EFFICACY OF MULTIVALENT FOOTROT VACCINES

A multivalent footrot vaccine has been developed, containing pilus ant igens produced in recombinant Pseudomonas aeruginosa and representing all nine serogroups of Dichelobacter (Bacteroides) nodosus commonly re cognised in the field. The responses of sheep to the multivalent vacci ne have been compared with those to monovalent vaccines representing o nly a single serogroup. Antigenic competition between serogroups occur red in sheep immunised with the multivalent formulation, but high leve ls of protection were still achieved. The study showed that in multiva lent footrot vaccines, antigenic competition is predominantly due to t he presence of a family of immunologically-related pilus antigens rath er than to interference by extraneous proteins.