Clostridium botulinum is an anaerobic, Gram-positive, rod-shaped bacterium known for causing Botulism. It is found as a variety of different strains, each producing its own deadly neurotoxin. Horses are usually affected by types A, B, C and D. C. botulinum is found in decaying organic matter and soil. The bacteria form spores which allow them to survive in a dormant state until exposed to conditions that can support their growth. C. botulinum can survive in the soil for years and is resistant to heat and most chemical disinfectants.