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(Note: other complex events also occur, including disruption of haemodynamics, monolobular fibrosis, egg-granulomas etc.)
(Note: other complex events also occur, including disruption of haemodynamics, monolobular fibrosis, egg-granulomas etc.)
*'''Black disease (Infectious Necrotic Hepatitis)''' - is caused by a toxin produced by ''Clostridium novyi'' type B. It is commonly associated with liver fluke infestation because:
*'''Black disease (Infectious Necrotic Hepatitis)'''
**caused by a toxin produced by ''Clostridium novyi'' type B.
**It is commonly associated with liver fluke infestation because migrating flukes → liver necrosis → anaerobic conditions → clostridial multiplication → toxin production → disease
==== Pathogenesis of chronic fasciolosis ====
*'''Bile duct damage'''
**Adult flukes (2-5cm long) in bile ducts feed on epithelium and blood
**Chronic inflammatory responses → fibrosis of bile duct wall (and, in cattle, calcification)
**Gamma glutamyl transpeptidase released by damaged cells
**Ulceration and haemorrhage of bile duct → epithelial hyperplasia and increased mucosal permeability
*'''Anaemia'''
**250 flukes → up to 50ml of blood loss daily → 10 times increase in rate of erythropoiesis → normochronic anaemia until iron stores are exhausted → hypochromic anaemia.
*'''Hypoalbuminaemia'''
**Albumin (and other plasma proteins) lost into bile duct because of
#Whole blood loss
#Increased epithelial permeability
** → Increased catabolic rate by 2.5x → increased nitrogen loss via urine
**The effects seen depend on the magnitude of nitrogen loss
#There is no obvious effect (although animal is still in abnormal physiological state)
#Reduced weight-gain and/or wool growth and/or milk production
#Loss of body tissue (i.e. weight-loss); hypoalbuminaemia → reduced plasma oncotic pressure → oedema
=== Adults in Bile Ducts ===
=== Disease manifestations ===
*'''Bile duct damage''' - adult flukes (2-5cms long) in bile ducts feed on epithelium and blood; chronic inflammatory responses → fibrosis of bile duct wall (and, in cattle, calcification).
*Large numbers of metacercariae ingested over a short period of time leads to acute disease
*'''Bile duct damage''' - adult flukes feed on biliary epithelium (gamma glutamyl transpeptidase released by damaged cells) and blood, leading to ulceration and haemorrhage, which causes epithelial hyperplasia and increased mucosal permeability.
*Smaller numbers ingested over a longer period of time leads to chronic disease
*'''Anaemia''' - 250 flukes can cause up to 50ml of blood loss daily → 10 times increase in rate of erythropoiesis → normochronic anaemia until iron stores are exhausted → hypochromic anaemia.
*'''Feed intake'''
*'''Hypoalbuminaemia''' - anaemia (and other plasma proteins) lost into bile duct because of:
**Fluke infections cause reduced food intake
NOTE: chronic fasciolosis occurs at a time of year when animals are on a low plane of nutrition. This combined with the reduced food intake causes a significant effect on the development and severity of clinical and subclinical fasciolosis.
*'''Species susceptibility'''
**The proportion of flukes that reach the bile ducts is determined mainly by
***The fibroplastic potential of the liver
***The effectiveness of the protective immune responses (which are ineffective in sheep)
**Therefore, establishment rate is
'''sheep>cattle>pig'''
=== Snail biology ===
=== Snail Biology ===
[[Image:Lymnaea truncatula.jpg|thumb|right|150px|''Lymnaea truncatula'' - Wikimedia Commons]]
[[Image:Lymnaea truncatula.jpg|thumb|right|150px|''Lymnaea truncatula'' - Wikimedia Commons]]
==== ''Lymnaea truncatula'' ====
==== ''Lymnaea truncatula'' ====
*is 5-10mm long
*5-10mm long
*has a brown-black shell with 5-6spirals
*Brown-black shell with 5-6 spirals
*first spiral is greater than half the total length
*1st spiral is greater than half the total length
*the shell opens on the right (when held with the opening upwards)
*The shell opens on the right (when held with the opening upwards)
*feeds on green slime
*feeds on green slime
*can multiply rapidly if food is abundant
*can multiply rapidly if food is abundant