Clostridum tetani (TETANUS)

Clostridium tetani, a Gram-positive rod that forms a terminal spore, is commonly
found in the soil, dust and animal feces. Contamination of wounds, which provide anaerobic conditions, can lead to spore germination and tetanus, a relatively rare, but frequently fatal disease. Tetanus is also know as lockjaw because of the patient’s inability to open the mouth as a result of muscle paralysis. Infection usually occurs when spores (in dirt, feces or saliva) enter wounds and scratches where they germinate and produce tetanus toxin. The organism is non-invasive and thus remains in the local wound.

The exotoxin (tetanospasmin) binds to ganglioside receptors on inhibitory neurones in central nervous system. The effect of the toxin – to block the release of inhibitory neurotransmitters (glycine and gamma-amino butyric acid) – it produces the generalized muscular spasms characteristic of tetanus. This stops nerve impulse transmission to muscle leading to spastic paralysis. The toxin can act at peripheral motor nerve end plates, the brain, spinal cord and also in the sympathetic nervous system. It is transported within the axon and across synaptic junctions until it reaches the central nervous system. Because inhibitory neurons are involved, the result is unopposed muscle contraction.
In generalized tetanus, the most common form, the patient typically experiences
lockjaw (trismus). This is a stiffness of the jaw muscles that results in inability to open the mouth or swallow leading to the appearance of a sardonic smile (risus sardonicus). Cephalic tetanus is a rare infection involving the middle ear. It can affect cranial nerves. Local tetanus is also rare and manifests itself as localized muscle contractions in the area of
infection.