VPA 211: General Veterinary Parasitology and Helminthology (3+1)

DEVELOPMENT IN THE VERTEBRATE HOST

• Following ingestion of metacercaria excystation occurs in the duodenum. Within 24 hrs of infection, the majority of immature trematodes occur in abdominal and peritoneal cavity.
• By 4 - 6 days after infection, majority will penetrate the liver capsule and found migrating in the liver parenchyma. Young fluke may reach the liver through blood stream but it is unusual. Usual route is via peritoneal cavity and migration in the liver may occurs upto 5 - 6 weeks.
• From 7th week onwards they enter the bile duct and reach the sexual maturity, some flukes may be seen in gall bladder also. During 8th week of infection eggs are passed in the faeces. Prepatent period is normally 8 - 12 week.
• Occasionally in cattle, the immature flukes may be found in the other organs, such as in lungs and in the pregnant animals, the parasite may occur in the foetus.
• Minimum period of completion of one life cycle (egg to egg) is 17 - 18 weeks in F.gigantica, under favourable condition.
  The longevity of Fasciola in untreated sheep may be years; in cattle, it is less than one year.

Metacercaria