Tetanospasmin

C. tetani is an obligate anaerobic, spore-forming gram-positive rod found in soil, with terminal spores giving a drumstick or tennis racket appearance. Spores germinate in devitalized, poorly perfused wounds such as puncture injuries, burns, and umbilical stumps in unimmunized neonates. The toxin is taken up at the neuromuscular junction and transported retrograde along the motor axon to the spinal cord, where it crosses into inhibitory Renshaw interneurons and cleaves synaptobrevin (VAMP), preventing vesicle fusion. The organism itself does not invade, so the clinical picture is entirely toxin-mediated and the wound may look trivial or have healed. Because the toxin binds irreversibly, immune globulin can only neutralize circulating unbound toxin, and recovery requires growth of new nerve terminals over weeks. The mirror-image toxin is botulinum, which cleaves the same SNARE family but acts peripherally on excitatory cholinergic terminals, causing descending flaccid paralysis with pupillary dilatation and dry mouth. Both are among the most potent toxins known.