Vaccination against ovine foot-rot

Sheep vaccinated in different ways or left unvaccinated, were challenged by the application of Fusiformis nodosus cultures after exposure of their feet to maceration and to faecal contamination as a source of F. necrophorus. Severe persistent foot-rot developed in 7 unvaccinated controls and 7 vaccinated with F. necrophorus only. Slight infections confined to the interdigital skin developed in 13 of 16 sheep vaccinated with the challenge strain of F. nodosus alone or in combination with F. necrophorus, but all except 3 of these had healed 30 days later. The F. nodosus vaccine was given to 6 sheep with severe foot-rot induced by the method of challenge. Eight weeks after the first dose they had healed completely, whereas 7 controls left unvaccinated were still severely affected. Six infected unvaccinated sheep were cured by parenteral chemotherapy and externally applied formalin. When challenged again they were still fully susceptible. The superior resistance of the vaccinated sheep was associated with titres of circulating bactericidal antibody far higher than those in the sheep that had been infected only. It is suggested that their resistance was due to the destruction of F. nodosus by antibody and complement diffusing into the infected epidermis.