Tetanus - Horse

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  • 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.

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