Clostridium tetani and Tetanus
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Direct answer
Clostridium tetani is a spore-forming, obligate anaerobic Gram-positive rod with terminal drumstick spores that causes tetanus. Its neurotoxin, tetanospasmin, blocks the release of glycine and GABA from inhibitory interneurons, producing unopposed muscle contraction and spastic paralysis. Infection does not confer lasting immunity, so prevention depends on tetanus toxoid and careful wound management.
What you must remember
- Morphology: motile Gram-positive obligate anaerobe with terminal spores that give a drumstick appearance, and spores persist for years in soil and manure.
- Tetanospasmin: an AB neurotoxin that binds gangliosides and travels by retrograde axonal transport to the spinal cord.
- Mechanism: the light chain cleaves synaptobrevin, so inhibitory interneurons cannot release glycine and GABA, and motor neurons fire unopposed.
- Incubation: usually about 3 to 21 days, and a shorter incubation period predicts more severe disease.
- Clinical features: trismus or lockjaw, risus sardonicus, opisthotonus and reflex spasms triggered by stimuli, with autonomic instability in severe cases.
- Clinical forms: generalised, localised, cephalic, and neonatal tetanus from contaminated umbilical cord care.
- Prophylaxis: tetanus toxoid, with human tetanus immunoglobulin for tetanus-prone wounds when vaccination is incomplete or unknown.
- National programme: India was validated as having eliminated maternal and neonatal tetanus in 2015.
Managing a contaminated wound
A farmer presents with a deep puncture wound from a rusty nail, and he has had only one tetanus dose in the past. The steps show how the team balances the risk of tetanus against the need for prompt wound care.
- Assess the wound: puncture, crush, burn, frostbite and contamination with soil, faeces or saliva all mark a tetanus-prone wound.
- Check vaccination history: a patient with fewer than three documented doses, or with an uncertain history, needs a toxoid dose now.
- Clean and debride: the wound is washed, devitalised tissue is removed and foreign bodies are excised, because necrotic tissue supports anaerobic growth.
- Give human tetanus immunoglobulin: it is given intramuscularly at a separate site from the toxoid, to neutralise toxin that has not yet bound to nerves.
- Start the antibiotic: metronidazole is the first-line agent against the organism, with penicillin as an alternative.
- Support the patient: a quiet room, benzodiazepines for spasms and mechanical ventilation for airway compromise are used if the disease progresses.
Where the exam tries to catch you
Tetanus questions turn on the transmission route, the immunity gained from disease and the drug given for the wound.
- Trap: assuming tetanus spreads from person to person Correct: the organism lives in soil and enters through wounds, so the disease is not transmitted between people.
- Trap: believing recovery from tetanus gives lasting immunity Correct: the illness does not produce protective immunity, so toxoid is still required afterwards.
- Trap: relying on immunoglobulin alone for established disease Correct: it neutralises only unbound toxin, so wound cleaning and spasm control remain essential.
Frequently asked questions
What is the mechanism of tetanospasmin in Clostridium tetani?
Tetanospasmin cleaves synaptobrevin in inhibitory interneurons of the spinal cord, which blocks the release of glycine and GABA. The result is unopposed motor neuron firing, leading to rigidity and painful spasms.
Why does tetanus cause trismus and risus sardonicus?
Trismus and risus sardonicus occur because toxin reaches the short motor nerves to the masseter and facial muscles first. These muscles are therefore often involved earliest in generalised tetanus, giving the characteristic lockjaw and fixed smile.
Which wounds are considered tetanus-prone?
Tetanus-prone wounds include puncture wounds, crush injuries, burns, frostbite, and wounds contaminated with soil, faeces or saliva. These wounds need toxoid and, where vaccination is incomplete, human tetanus immunoglobulin.
How is neonatal tetanus prevented?
Neonatal tetanus is prevented by hygienic umbilical cord care and by vaccinating pregnant women with tetanus toxoid (Td in the current UIP schedule). India was validated as having eliminated maternal and neonatal tetanus in 2015, following these measures.
Which antibiotic is the first choice in tetanus?
Metronidazole is the first-line antibiotic in tetanus, with penicillin used as an alternative. Antibiotics kill the organism but do not neutralise toxin already bound to nerves, so wound care and immunoglobulin remain essential.