The obligate anaerobe C. tetani is a spore-bearing Gram-positive bacillus. Spores are found in animal and human feces and exist ubiquitously in soil. C. tetani cannot breach intact skin or mucous membranes; the portals of entry include puncture wounds, lacerations, surgical wounds, burns, gangrene, chronic ulcers, dog bites, injection sites, dental infections, otitis media, and the genital tract following abortion or childbirth. The injury itself may be trivial, and in up to 20 per cent of cases there is no history or evidence of a wound. Clostridial spores germinate in oxygen-poor environments (e.g. necrotic tissue) and toxins are liberated by vegetative forms. C. tetani infections remain localized, but the toxin is distributed widely via the bloodstream, taken up into endings of motor nerves, and transported into the nervous system. Motor neuron endplates in skeletal muscle are affected by decreasing release of acetylcholine. Decreased neurotransmitter release by spinal neurons impairs polysynaptic reflexes and causes autonomic dysfunction.
The pathogenesis of tetanus is summarized in Table 1.
Table 1 Pathogenesis of tetanus
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