Tetanus - Horse

Also known as:

Lockjaw

• In a pathological context, "tetanus" is an infectious disease caused by the bacterium Clostridium tetani.
  • Physiologically, the term "tetanus" refers to continuous sustained muscle contraction.
    • The disease caused by Clostridium tetani is characterised by this feature.

Pathogenesis

• Clostridium tetani generally cause infection via wound contamination.
  • Cuts or deep puncture wounds are most commonly infected.
• Clostridium tetani produces tetanospasmin, a neurotoxin.
  • Tetanospasmin inhibits the release of the neurotransmitters GABA and glycine from interneurons in the spinal cord and brain.
• Without the usual inhibitory influence of glycine and GABA, there is increased excitation of the brainstem and motor neurons.
  • This leads to unopposed muscle contraction.
    • The frequency of action potentials at the neuromuscular junctions increases above a threshold.
    • Above this threshold, muscle fibres enter a state of tetanus.
      • Muscle spasm is initially present in the muscles of the jaw.
      • This is followed by a difficulty in swallowing.
      • General muscle stiffness and spasms then develop in other parts of the body.
  • Other effects may include:
    • Seizures
    • Effects on the autonomic nervous system

Diagnosis

• Diagnosis is made by taking into account the animal's:
  • History
  • Clinical signs
• Very rarely a wound where the bacteria may have entered may be seen.

Treatment

• Wound debridement
  • Surgical removal of dead and infected tissue from the wound.
• Antibiotic treatment.
  • Metronidazole
    • Treatment with metronidazole decreases the number of bacteria but has no effect on the bacterial toxin.
    • Metronidazole is particularly active against anaerobic bacteria, and so is a good choice for use against C. tetani
  • Penicillin
    • Penicillin is becoming a less favoured treatment for tetanus, since there is a theoretical risk of increased spasms.
• Muscle relaxants
  • Diazepam
  • Midazolam
• Supportive therapy, for example:
  • Administering fluids
  • Providing appropriate nutrition
  • Maintaining a quiet environment with dimmed light.
• Remission take several weeks to months