Special Veterinary Pathology

FASCIOLIASIS

Definition

• Fascioliasis is a very important disease of cattle in India and is caused by Fasciola hepatica and Fasciola gigantica
• Fascioloides magna, a large liver fluke occurs in the liver of cattle,sheep, horse,deer and raely pigs.

Aetiology

• Fasciola hepatica and Fasciola gigantic

Incidence

• It is a very important disease of cattle in India

Pathogenesis

• Infection is by ingestion
• It is a hermaphrodite and reproduces by depositing ova in the biliary passages, through which they reach the intestine and are then passed in the faeces
• Intermedaite host: Lymnaea sp.
• Following ingestion, infective metacercariae encyst in the duodenum, penetrate wall and reach peritoneum causes peritonitis and penetrate the liver reach bile duct where they become mature flukes cause chloangiohepathitis, irritate and obstruct the bile duct and predispose to bacterial infection.
• Fascioloides magna, the infective forms penetrate the intestineal wall, and wander around in the peritoneal cavity before invading the liver

Clinical signs

• Acute, subacute and chronic forms. Subacute and acute forms in sheep are usaually fatal- Damage to liver but death due to haemorrhages and anaemia
• Chronic: Anaemia, unthriftiness, submandibular oedema and reduced milk secretion

Gross lesions

• May be due to the adult fluke in the bile duct(obstructive jaundice) or due to wandering ones in through parenchyma.
• Wandering flukes produces lesions of traumatic nature which appear as haemorrhagic foci and in the form of tortuous tunnels.
• Liver is firmer and harder to the touch and cuts with difficluty
• The bile ducts in advanced cases  especially in cattle, are hard and calcified - Pipe stem appearance or clay pipe liver and when cut,  a grating sound is elicited.
• In early cases, hepatic cells show degenerative changes and eosinophilic inflammation and later histiocyte and giant cells invades the necrotic area of coagulative type.
• Cyst formation with calcification may also be seen
• Chronic obstruction of biliary passage may result in “clay pipe cirrhosis"

Microscopic lesions

• Cholangiohepatitis, biliary epithelium is stimulted to papillary and glandular hyperplasia.
• The walls of the ducts become infiltrated with eosinophils, lymphocytes, and macrophages and ultimately become thickened  from fibrous proloferation.
• Extensie fibrosis and calcification of te bile ducts give rise to the term "pipe stem liver" /"clay pipe liver"
• Small granulomas may form around eggs that become lodged in small bile ducts

Diagnosis

• Identification of characteristic ova in the faeces- oval, pedunculated, golden brown eggs
• Postmortem lesions in the liver