Category:Hepatitis, Parasitic

Liver Nematodes

Cestodes

• tapeworms
• have both intermediate and final hosts in their life cycle
• main expression in the UK are the encysted forms that utilise the liver and other organs in intermediate hosts

Taenia hydatigena

• the most important species
• final host
  • dog
  • alimentary tract
• intermediate host
  • ruminant, horse, or pig
• life cycle is completed when the carnivore eats the tissues of the intermediate host containing the cysts
• the intermediate stage - Cysticercus tennuicollis
  • fluid filled cysts on the surface of the liver and in the peritoneal cavity

NB: other Taenia species have muscle and brain as preferred sites in the intermediate hosts

Some can infect humans - zoonoses

Echinococcus granulosus

• Hydatid Disease
• final host
  • dog, fox, and other canids
• intermediate host
  • sheep most commonly affected
  • ox and horses

NB: can also affect man - zoonosis

• hydatids - the cyst form
  • develops from the ova
  • occur in the lung and liver
  • cysts are usually multiple
  • 5-10cm in diameter
  • contain a clear fluid with numerous scolices or "hydatid sand"
  • the small calcified lesions that are sometimes present in the liver of sheep may represent degenerate hydatid cysts
  • can be very prevalent in some geographical areas

Trematodes

• flukes are important pathogens of the liver
• Fascioliasis is among the most important parasitic conditions of sheep and cattle and is common

Fasciola hepatica

• common liver fluke
• intermediate host
  • aquatic snails
  • therefore infestation is more common in damp or poorly drained pastures
• final host
  • cattle and sheep
• can cause severe haemorrhagic liver damage
• death in heavy infestations in sheep during migratory phase (1 month) through the liver tissue
• recovered animals will have scarred livers
• more commonly associated with chronic bile duct inflammation - cholangitis [need link to below]
  • the adults live in the bile ducts

Acute Fascioliasis

• acute disease associated with immature fluke migration through the liver
• occurs in late autumn and winter
• severity of outbreaks depend on a number of epidemiological factors
• the liver of animals which die of this disease will be
  • enlarged
  • haemorrhagic
  • honeycombed with the tracts of migrating flukes
    • tracts become filled with blood and degenerate hepatocytes later infiltrated with eosinophils, lymphocytes and replaced by fibrosis
  • surface is covered with a fibrinous peritonitis, especially the ventral lobe
  • subcapsular haemorrhages are frequent
  • rupture into the abdomen is not an uncommon finding

Chronic Fascioliasis

Gross

• liver is reduced in size, unevenly
  • left lobe is most severely affected with atrophy of the extremities
• hypertrophy may occur in some cases
  • dorsal lobe
  • this changes size and distorts shape of liver
• the surface will be uneven with areas of fibrous tissue replacing the cells damaged by the migrating flukes
• bile ducts
  • prominent thick protruding white bile ducts on the visceral surface spreading from the hilus to the left lobe
  • the bile ducts are dilated, black, and calcified on cut surface
  • numerous adult flukes can be expressed from the bile ducts
  • chronic cholangitis
  • 'pipe stem' appearance in cattle because bile ducts are very much thickened and often calcified
• bile
  • dark brown, thick, and gritty in consistency

NB: the fibrosis which occurs in the chronic stage is realted only partly to the healing of the migratory tracts and the rest may be related to the development of immunity and rechallenge

Microscopically

• reactive hyperplasia of the bile ducts
• substantial inflammatory cell infiltrate and peripheral fibrosis
• calcification of the chronically damaged tissue

Protozoal

Toxoplasmosis

• Toxoplasma gondii
• broad host range
• characterised by widespread necrosis in many organs
• liver lesions
  • appear as disseminated foci of necrosis with little or no inflammatory reactions
  • white or yellow foci are visible on the surface