Infectious Necrotic Hepatitis

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

Clinical

• 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

Gross

• 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

Microscopically

• 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

Treatment

• rarely possible
• Penicillin or Oxytetracycline at very high doses

Prevention

• vaccination
  • normally lasts up to 6 months
• liver fluke control
• remove dead carcasses from pasture