Pathogenesis

PATHOGENESIS

  • C.tetani has little invasive power. The endospores enter traumatized tissue or surgical wounds, especially after castration or docking, via the umbilicus or into the uterus, following dystocia in cattle and sheep.
  • The spore implanted in a wound can germinate and multiply only if the conditions are favourable.
  • Destruction and necrosis of tissue, lack of drainage in the area, presence of extraneous matter especially of soil, all create anaerobic conditions and favour germination of C.tetani spores.
  • The resultant vegetative cells multiply at the site and produce the potent tetanospasmin.
  • This travels via peripheral nerves or blood stream to ganglioside receptors of the motor nerve terminals and eventually to cells of the ventral horn of the spinal cord, thus affecting many groups of muscles at various levels.
  • The toxin acts presynaptically on motor neurons, blocking synaptic inhibition and causing a spastic paralysis and the characteristic tetanic spasms.
  • Tetanospasmin binds specifically to gangliosides in nerve tissue and once bound cannot be neutralized by antitoxin.
  • When toxin travels up to a regional motor nerve in a limb, tetanus first develops in the muscles of that limb, then spreads to the opposite limb and moves upwards.
  • This is known as ascending tetanus and is usually seen only in the less susceptible animals such as dogs and cats.
  • Descending (generalized) tetanus is the common form in susceptible species such as human and horses.
  • In this form toxin circulating in the blood stream affects the susceptible motor nerve centers that serve the head and neck first and later the limbs. Once established, signs of tetanus are similar in all animals.
Last modified: Monday, 4 June 2012, 4:25 AM