An anamnestic serological test for ovine footrot

Following recovery from ovine footrot, a proportion of sheep in a flock may carry the causative organism and spread it to other sheep if environmental conditions are favourable. Footrot affected sheep have elevated levels of serum antibody against Bacteroides nodosus, but these levels decline rapidly after clinical recovery. When challenged by subcutaneous injection with 470 micrograms of protein extracted from the cell membrane of B. nodosus, without adjuvant, sheep that had recovered clinically from virulent footrot produced a marked increase in specific serum antibody within 7 d, while antibody levels in footrot-free sheep injected with the same antigen, and in saline injected controls, did not increase over a period of 25 d. Artificial stimulation and serological detection of immune memory may be useful in footrot eradication programs by identifying sheep that have had clinical footrot infection. This procedure may be applicable to other diseases where antibody responses are inconsistent or transient.