Difference between revisions of "Infectious Necrotic Hepatitis"
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*[[Liver - Anatomy & Physiology|liver]] fluke control | *[[Liver - Anatomy & Physiology|liver]] fluke control | ||
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Revision as of 12:39, 12 June 2010
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
- 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