An overview of botulism was given at the 2009 WEVA Congress by Nathan M. Slovis DVM, Dipl. ACVIM, CHT (certified in hyperbaric oxygen therapy), director of the McGee Critical Care and Medical Center at Hagyard Equine Medical Institute in Lexington, Ky.

He described botulism as a neuromuscular disease characterized by flaccid paralysis and caused by neurotoxins produced by strains of Clostridium botulinum. He noted horses are one of the most susceptible species to botulism, with both individual and group outbreaks having been reported around the world.

C. botulinum was first identified in 1897 in Belgium during an outbreak of food poisoning traced to imperfectly smoked ham. Clostridium tetani, the organism that causes tetanus, is a close relative. The toxin produced by C. botulinum is one of the most potent known to man–in fact, it has at times been considered a weapon of biological warfare. Since horses are particularly sensitive to botulinum toxin, untreated foals can suffer up to 90% mortality, with adult horses approaching 100%.

"Clostridium botulinum is a Gram-positive, spore-forming anaerobic bacterium," Slovis said. "Spores are found in the soil throughout most of the world, with the distribution of strains dependent on temperature and soil pH. Eight serotypes of botulinum neurotoxin exist and are labeled A, B, C1,C2, D, E, F, and G, all of which have similar toxicity. There is geographic variation in the predominant serotypes. In North America, botulism in horses is most often caused by Type A and B toxins, and less often C