Incubation of Clostridium tetani ranges from 3-21 days, with the average being around 8-10 days. The distance between the point of bacillus entry (wound) and the central nervous system (CNS) influences the incubation period, with the further the wound is from the CNS the longer the incubation period.
Wounds of the head, neck and trunk typically have the shortest incubation periods. The length of incubation period also influences the severity of the disease, longer incubation (10 days or more) typically results in more mild disease than a shorter incubation period (7 days or less).
Tetanus is diagnosed on clinical grounds. A history of contaminated wound may or may not be present. Laboratory testing e.g., wound cultures, cannot confirm or exclude the diagnosis. Strychnine poisoning mimics tetanus, without a raised body temperature. Other differential diagnoses include dental caries/disease, tonsillitis, parotitis, temporomandibular joint (TMJ) disease, Bell’s palsy, low serum calcium and dystonic reactions to medication.
Tetanospasmin travels to the CNS via the axons and irreversibly binds to the neuromuscular junction nerve terminals, blocking the release of inhibitory neurotransmitters that cause muscle relaxation. Tetanospasmin may also cause autonomic nervous system (ANS) dysfunction.
Localised tetanus is rare in humans; spasms are confined to an area close to the wound, may be mild and may resolve spontaneously over several weeks to months or may progress to generalised tetanus.
Generalised tetanus is characterised by generalised muscular rigidity and prolonged, tonic contraction spasms often triggered by external stimuli. Initial symptoms include weakness, stiffness or cramps, and difficulty chewing or swallowing food progressing to the person’s inability to open their mouth (trismus), a characteristic facial grimace (risus sardonicus) and arching of the back (opisthotonus).
The person with tetanus may cause trauma to their tongue. Muscle spasms can be severe enough to cause fractures of the vertebrae and long bones and can raise the person’s body temperature by 2-4°C.
ANS dysfunction may present as hypertension, hypotension, flushing, sweating, urinary retention, tachycardia and arrhythmias.
A person with tetanus remains conscious and alert, unless they develop upper airway obstruction and become severely hypoxic. Spasm of the glottis can cause immediate death.
Cephalic tetanus is rare and usually associated with a wound on the head. Following a short incubation period, 1-2 days, the person presents with atonic cranial nerve palsies (facial paralysis) involving nerves III, IV, VII, IX, X and XII, singly or in combination. Trismus may be present and cephalic tetanus may progress to generalised tetanus.
Tetanus neonatorum (neonatal tetanus) is the most common presentation of tetanus in developing countries. It is a form of generalised tetanus arising from infection of the umbilical stump. Mortality exceeds 90%. Babies who survive may experience long term consequences including subtle intellectual and behavioural abnormalities, cerebral palsy and severe psychomotor retardation.
The acute clinical course of tetanus varies between 1-4 weeks. Approximately 10% of people who get tetanus die, despite the modern intensive care units, machines and medicines. Those who survive usually have a full recovery after rehabilitation.