Pathology

Tetanus is caused by clostridium tetani - an anaerobic, flagellated, exotoxin-secreting, Gram-positive bacillus that forms a characteristic terminal spore ('drumstick').

• the spores are widespread in the environment (commonly found on soil, faeces and dust) and can survive in hostile conditions for long periods of time (1)
• the spores are introduced to the body after the contamination of an abrasion or minor puncture wound (which may go unnoticed), through injecting drug use and occasionally through abdominal surgery (2). The organisms remain and multiply at the site of inoculation.
• but in around 20% of the patients, no entry site can be found

It produces a powerful exotoxin - tetanospasmin - which acts on the motor cells in the CNS and which is probably conveyed along the peripheral nerves directed from the affected part.

• tetanospasmin interferes with the release of glycine and γ-amino butyric acid (GABA) thereby affecting the inhibitory pathways
• the toxins binds irreversibly to the neurones and recovery requires the growth of new nerve terminals (1)

Often, progress to clinical tetanus may seem unrelated to the degree of the initial insult; thus an extensive injury which has received early and adequate wound toilet is far less at risk than a contaminated puncture wound which has been neglected.

In primitive communities, where dung is used to dress the umbilical cord in the newborn, tetanus neonatorum may occur.

Reference:

• (1) Taylor MA. Tetanus.Contin Educ Anaesth Crit Care Pain 2006;6(3):101-104