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Microbiology, Epidemiology, and Pathogenesis
Tetanus is characterized by increased muscle tone and spasms caused by tetanospasmin (“tetanus toxin”), a toxin produced by Clostridium tetani.
- C. tetani is a spore-forming, anaerobic gram-positive rod that is ubiquitous in soil and whose spores are highly resilient.
- Tetanus is a rare disease in the developed world: only 231 cases were reported in the United States between 2001 and 2008. Most cases occur in incompletely vaccinated or unvaccinated individuals.
- After spores contaminate wounds (typically puncture wounds or, in the case of neonates, the umbilical stump) and reach a suitable anaerobic environment (e.g., devitalized tissue), organisms proliferate and release toxin.
- The toxin blocks release of inhibitory neurotransmitters (glycine and γ-aminobutyric acid) in presynaptic terminals, and rigidity results from an increased resting firing rate of the α-motor neurons.
- A toxin dose as low as 2.5 ng/kg can be fatal.