Grass Sickness

Equine dysautonomia, or grass sickness

• Most prevalent in the UK and western Europe.
  • Common in wetter areas, e.g. the South West.
• Seen in horses out at pasture in late summer and autumn.
• Usually affects young adults.
  • 6-7 years old.
• Clinical
  • Acute oneset:
    • Muscular tremors
    • Abdominal pain
    • Does not eat
    • Constipation
    • Become severly tympanic in acute cases
    • Dull and restless
    • Avoid swallowing
    • Salivate excessively
  • Degenerative lesions are seen in the autonomic nerve ganglia, including enteric plexuses
  • May either:
    • Progress rapidly to death
    • Take a slower clinical course.
      • Eat a bit, but food drops out of mouth
      • Go on to die slowly.
  • Some horses recover
    • This is very unlikely, and the condition is usually fatal.
  • Clinically difficult to diagnose - signs are confined to the gut.
    • Easy to diagnose on post mortem
• Pathology
  • Stomach and small intestine large amounts of contain watery yellow fluid.
    • There is an abrupt change in the large intestine, where no fluid is present.
      • large intestine has very dry mucoid contents.
• Pathogenesis
  • Due to functional obstruction at ileocaecal valve and a degree of paralytic ileus of the small intestine.
  • The exact cause is unknown, but a type of bacterial or fungal toxin which may damage autonomic nervous system ganglia may be involved.
    • Clostridium botulinum is thought to be involved.
• A similar condition seen in hares
  • Certain yeares almost seem to have outbreaks.
• Certain pastures at certain times of year produce grass sickness quite often.
  • A definitive diagnosis must be made - if the condition is due to the grazing we need to know.
    • E.g. if on livery or stud grazing, may put people off going there.
• 'Diagnosis
  • At post mortem look for degenerative changes in coeliaco-mesenteric ganglia - need to examine histologically.
    • Ganglia are peanut sized and found in perirenal fat between adrenal gland and the aorta.