ASC-173: Botulism: A Deadly Disease That Can Affect Your Horse

B 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, sporeforming 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. The bacterium and its spores are widely distributed in nature. They are found in soil, sediments of streams and lakes, and in the intestinal tracts of fish and mammals. The bacteria will produce toxins under conditions of decaying plants and animals. A horse can get botulism in three ways: • By consuming forage or feed containing the bacteria, which will then produce the toxins in the intestinal tract (more commonly found in foals, known as shaker foal syndrome, or toxicoinfectious botulism). • By consuming feed or forage containing the pre-formed toxins of C. botulinum (known as forage poisoning). • Through wounds contaminated with the bacteria, generally puncture wounds. Wound borders will close, providing an anaerobic environment, which is a favorable condition for the bacteria to produce the toxins.