Botulism is a deadly disease caused by the toxins produced by the bacterium Clostridium botulinum. The botulinum toxin is a potent neurotoxin that impairs nerve function, including those of the diaphragm, leading to paralysis. When the nerves to the diaphragm are paralyzed, the affected animal stops breathing and will die as a result.

C. botulinum is an anaerobic (lives without oxygen), Gram-positive, spore-forming bacterium. The toxin produced by C. botulinum is one of the most potent toxins known to science. The Clostridium family is known for causing rapid, severe, and deadly diseases, including botulism, tetanus, blackleg, malignant edema, etc. Sometimes the onset of clostridial disease is so rapid that no clinical signs are noted, and the owner simply finds the animal dead.

The botulism toxin blocks the release of acetylcholine in the neuromuscular junction. Acetylcholine is a neurotransmitter, which transmits information from the nerve cell to the muscle cell. It is released in the neuromuscular junctions (the space where nerves communicate and stimulate muscles), and it enables muscle contraction; therefore, without acetylcholine, the muscles will not contract. A very important muscle in any mammal’s survival is the diaphragm, which, when contracted, enables breathing. Ultimately, without acetylcholine, a horse infected with botulism will die of respiratory failure and asphyxia, due to the paralysis of the diaphragm.

There are seven types of botulism recognized (A, B, Ca, Cb, D, E, F, and G), based on the antigenic specificity of the toxin produced by each strain. Types A, B, E, and F cause human botulism. Types A, B, C, and D cause most cases of botulism in animals. In horses, Type B botulism is responsible for more than 80% of the cases