Experimentally induced toxicoinfectious botulism in horses and foals.

Four experiments were performed to elucidate the pathogenesis of toxicoinfectious botulism in horses and foals. Groups of horses and foals were inoculated with one of the following: (1) crude toxin of Clostridium botulinum, type B, given IV, (2) C botulinum spores, given IM, (3) C botulinum spores, given IM, in necrotic lesions, and (4) C botulinum spores, given orally with and without dexamethasone. Toxin of C botulinum in minute amounts is toxic to horses. Clostridium botulinum spores produced toxicosis only when necrotic lesions were present. When C botulinum spores were given orally, they were innocuous. Toxicosis occurred when dexamethasone and C botulinum spores were given orally to a foal with necrotic lesions. Corticosteroids appear to predispose foals to the disease. In the animals where C botulinum organisms infected necrotic lesions, the clinical signs and the lesions seen on necropsy were identical with those seen in spontaneously occurring toxicoinfectious botulism.