Footrot is a contagious disease of small ruminants which is primarily caused by the bacterium Dichelobacter nodosus. The virulent form causes severe economic losses and also is a very significant animal welfare concern. Sheep and goats can be vaccinated for treatment, prevention and control of the disease. There are 10 different serogroups of D. nodosus (A,B,C,D,E,F,G,H,I,M) and immunity is serogroup-specific. The identification of the serogroup(s) of D. nodosus present in a flock is a prerequisite to specific (target) vaccination. Flocks and individual sheep can be infected with multiple serogroups. To control the disease, vaccines need to contain antigens against the serogroups that are present in the flock. When all ten serogroups are presented together in a vaccine, protection persists for only a few months due to “antigenic competition”. When vaccines are used as monovalents or bivalents, they induce protective antibody levels for much longer. It has been shown clearly in studies in Nepal, Bhutan and Australia that this can lead to eradication of the disease.
We evaluated the use of sequential monovalent or bivalent vaccines to control/eradicate virulent footrot on 12 commercial farms across areas of high footrot prevalence in southeast Australia. Where only one or two serogroups were present in a flock the clinical response to vaccination was very good; footrot was eradicated from a number of the trial flocks which had 3 or fewer serogroups at the start of the trial. Where there were more than 3 serogroups present, several rounds of vaccination were required for control and eradication of the disease. These results provide evidence for control and eradication of virulent footrot by sequential, flock-specific vaccination in Australia.