Tetanus is caused by a neurotoxin from Clostridium tetani (gram positive bacillus). Hallmark symptoms of tetanus are muscle rigidity, spasms and in severe cases autonomic nervous system disturbances. C. tetani is ubiquitous in the environment and survives as spores until encountering anaerobic conditions.
Tetanus is preferentially taken up by motor neurons and transported retrograde up the axon. It crosses the synapse and enters the presynaptic GABA G receptor. The toxin is a zinc-dependent endopeptidase that cleaves vesicle-associated membrane protein II in the presynaptic neuron. This membrane protein is essential for the synaptic release of neurotransmitters. Tetanus preferentially affects GABA inhibitory interneurons afferent to motor neurons in the spinal cord and brainstem. The result is unrestricted motor neuron activity resulting in increased tone.