Difference between revisions of "Infectious Necrotic Hepatitis"

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[[Category:Alimentary Diseases - Sheep]][[Category:Alimentary Diseases - Cattle]][[Category:To_Do_-_Clinical]]
[[Category:Alimentary Diseases - Sheep]][[Category:Liver Diseases - Cattle]][[Category:To_Do_-_Clinical]]

Revision as of 16:41, 17 January 2011

Infectious Necrotic Hepatitis (Black Disease)

  • Clostridium novyi type B
  • grazing animals
    • mainly sheep, also cattle (and reported sometimes in horses and goats)
  • organism is widely distributed within the soil and normally present in GIT and liver of grazing animals on infected pastures
    • worldwide
  • it is ingested by the animal and spores are absorbed via the gut and travel to the liver , where they lie dormant in macrophages (Kupffer cells) - also found in bone marrow and spleen
  • seasonal disease associated with Fasciola liver flukes
    • migrating immature liver flukes precipitate the disease
    • causes liver damage which provides ideal anaerobic conditions for the activation and germination of spores
  • C. novyi produces three exotoxins
    • alpha - a lethal toxin
    • beta - a lecithinase which is both haemolytic and necrotising
    • zeta - a haemolytic toxin
  • acute toxaemia produced by organism
    • affected animals are usually found dead because death is sudden due to the action of the powerful bacterial endotoxins
    • not all animals will become sick - only when organism starts producing toxin
  • post mortem changes occur rapidly
  • found dead/sudden death
    • well conditioned sheep 2-4 years old
    • lateral recumbency, few signs of struggle
    • vaccination history (against Clostridium)
    • no red urine or other bleeding
  • IF seen alive
    • severe depression
    • not eating
    • pyrexia
    • hypothermia
    • respiratory distress
    • muffled heart sounds
  • rapid decomposition of carcass
  • extensive subcutaneous vessels engorged and haemorrhage causing dark colouration of the skin - hence the name 'Black Disease' - and oedema
  • blood stained fibrinous fluid in abdomen, thorax, and pericardium which clots on exposure to air
  • tissues are autolysed
  • liver swollen and congested
  • characteristic pale (greyish-yellow) foci (3cm diameter) of necrosis surrounded by a rim of haemorrhage where the bacteria have multiplied upon incision
  • evidence of liver fluke
  • other organs show general signs of toxaemia

NB: Distinguish Black Disease from Red Water! The former will have several small areas of necrosis while the latter has one big lump

  • coagulative necrosis
  • possible evidence of migrating flukes
  • demonstration of bacteria
    • in the necrotic tissue
    • especially near its junction with viable tissue
    • rim of neutrophilic cells
  • rarely possible
  • Penicillin or Oxytetracycline at very high doses
  • vaccination
    • normally lasts up to 6 months
  • liver fluke control
  • remove dead carcasses from pasture

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