Difference between revisions of "Category:Hepatitis, Bacterial"

Hepatic Abscessation

Bacillary necrosis

• Fusobacterium necrophorum
• calves and lambs
• common in intensively reared beef cattle
• occurs following an infected umbilicus in neonates and from rumenitis in adult cattle

Gross

• rounded pale multiple foci of coagulative necrosis throughout the liver
• unsoftened, greyish-yellow patches
• ringed by a zone of hyperaemia
• foci coalesce in severe cases
• in adult animals, these lesions may have progressed to abscesses following lysis of the coagulated necrotic tissue and the formation of fibrous capsule around the damaged tissue
• if animal survives, these lesions may soften develop into abscesses

Microscopically

• coagulative necrosis
• possible evidence of migrating flukes
• bacteria can be demonstrated in the periphery of the necrotic tissue, especially near its junction with viable tissue
• there is a rim of neutrophilic cells

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

Bacillary Haemoglobinuria (Red Water)

• Clostridium haemolyticum AKA Clostridium novyi Type D
• cattle and sheep
• highly fatal
• similar pathogenesis to C. novyi
• beta toxin produced
  • causes hepatic necrosis and intravascular haemolysis
• C. haemolyticum found in soil, poorly drained/wet pastures
• spores found routinely in liver and GIT and faeces of grazing animals in affected pastures
• need disease in liver casing anaerobic conditions to allow bacterial growth and toxin production
• normally associated with Liver Fluke damage
• disease occurs in some areas and some farms - distribution is poorly understood

Clinical Signs

• found dead/sudden death
  • lateral recumbency
  • bloat
  • little signs of struggle
  • blood in nostrils, mouth, rectum, vagina
• IF seen alive
  • depressed, reluctant to move, pyrexia, respiratory distress
  • red urine (haemoglobinuria) but not consistent
  • pale mucous membranes/jaundice
  • bloody froth in nostrils

Gross

• post mortem is confirmatory finding
• rapid decomposition of carcass
  • organs decomposed
• subcutaneous hameorrhages, odema, emphysema
• blood stained abdominal and thoracic fluid, large quantity and pericardium
• animal is severely anaemic
• may be jaundiced
• red urine in bladder, therefore haemoglobin in urine
• kidneys speckled with haemoglobin
• blood in lungs/trachea
• ischaemic hepatic infarct
  • usually a single large necrotic focus in the liver
  • area of necrosis, sometimes partially liquefied centre, irregular outline with a hyperaemic edge

Microscopically

• presence of Clostridia post mortem must be interpreted with great caution as they are common post mortem invaders
• FAT for organism
• identification of toxins
  • need this for diagnosis

Treatment

• unlikely
• very high doses of penicillin or oxytetracycline
• blood transfusion

Prevention

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

NB: Distinguish Red Water from Black Disease! The former will have bleeding out of any orifice while the latter does not

Tyzzer's disease

• Bacillus piliformis
• affects
  • mostly laboratory rodents
  • possibly foals 1-4 weeks of age
  • young immune-compromised pups and kittens
• initial intestinal lesions can be hard to find at post mortem examination

[image from smythes' ppt] wheat sheaf

Leptospirosis

• Leptospirosis icterohaemorrhagica - a septicaemic disease which affects the liver
• puppies
• Leptospirosis is an important spirochaetal group of diseases causing disease in animals and humans (zoonotic)
• Transmission
  • via urine of affected animals
  • organisms can remain viable for weeks in damp conditions
• method of action
  • cause anaemia via intravascular haemolysis

Clinical

• fever
• dehydration
• haemorrhaging from the mucous membranes of the body

Diagnosis

• dark field microscopy on fresh urine is best

Gross

• widespread hameorrhages
• icterus
• pale foci in the liver (not always a constant finding)
• subcapsular and cortical renal haemorrhages

Microscopically

• foci of necrosis
• dissociation of hepatocytes form each other (similar to post mortem change)
• substantial haemosiderin in the Kuppfer cells (from the haemolysis)
• need to use a silver stain or immunofluorescence to demonstrate the organisms in tissues

Salmonellosis

• Salmonella dublin
• calves

Clinical

• fever
• dehydration
• diarrhoea

Gross

• severe, often haemorrhagic, inflammation in the ileum
• paratyphoid nodules - pale foci of necrosis in the liver

Microscopically

• foci of hepatocytic necrosis
• mixed mononuclear inflammatory cell infiltrate

NB: small foci of hepatocytic necrosis are often found as incidental lesions at post mortem examination

Other bacteria causing liver lesions

Mycobacterium tuberculosis

• in all species
• causes granulomas

Actinobacillus equuli

• foals
• bacteria from the septicaemia localise in the liver and other tissues, including the kidney

Nocardia species

• dogs
• cause pyogranulomatous foci