Comparing the efficacy of a new multivalent vaccine to a bivalent vaccine and foot-bathing for the treatment and control of ovine footrot in australian merinos

Jones, Jeremy
University of Sydney


Virulent footrot is an infectious disease of small ruminants which causes severe lameness and is a major welfare and economic concern. The causative bacterium, Dichelobacter nodosus, has ten immunologically distinct serogroups (A-I, M). Footrot can be controlled with a vaccine containing the recombinant fimbrial antigens of D. nodosus. Serogroup-specific monovalent and bivalent vaccines are highly effective against flocks containing one or two serogroups, respectively. However, multivalent vaccines targeting all serogroups have limited efficacy due to antigenic competition. In this study, a new multivalent vaccine formulation targeting nine serogroups (A to I) will be compared to a gold-standard bivalent vaccine and traditional foot-bathing in a Tasmanian Merino flock containing virulent footrot serogroups A and G. Foot lesions and antibody titres will be assessed monthly for 3 months to compare the initial therapeutic efficacy and immunogenicity of the treatments. Unfortunately, persistent environmental temperatures below 10°C resulted in reduced disease prevalence amongst all treatment groups, and therefore the initial therapeutic efficacy of the multivalent vaccine could not be determined. Results indicate that both the multivalent and bivalent vaccines induced significantly greater antibody titres than foot-bathing. Further, the titre was significant enough to provide partial protection against footrot, suggesting that the new multivalent formulation has overcome antigenic competition and would therefore be efficacious in a footrot control or eradication program. Continued monitoring of clinical lesions and antibody titres will be essential to accurately assess the long-term therapeutic and immunological efficacy of the multivalent vaccine