Changes

Development from miracidium into metacercariae takes around 6-7 weeks under favourable conditions, however, this period can be much longer in unfavourable conditions.

Development from miracidium into metacercariae takes around 6-7 weeks under favourable conditions, however, this period can be much longer in unfavourable conditions.

The final host, or the definitive host then ingests the metacercariae from the grass on the pasture, and these pass through the body into the intestine, where they excyst in the wall of the small intestine.  They then travel through the wall of the gut, and migrate into the liver, through the liver parenchyma. The young liver flukes migrate through the liver for around 6-8 weeks before entering the bile ducts. They may also migrate into the gall bladder, where they reach full sexual maturity.

Upon ingestion by the final or definitive host from the grass, metacercariae  excyst to present as immature  flukes in the small intestine. These then migrate across the peritoneal  cavity over a period of roughly one week, and invade the liver. Larvae continue to migrate within the hepatic parenchyma, becoming more destructive as they grow to a length of up to one centimetre. The young liver flukes migrate through the liver for around 6-8 weeks before entering the bile ducts where they mature to adults and begin to produce eggs. They may also migrate into the gall bladder, where they reach full sexual maturity.

The prepatent period of ''Fasciola hepatica'' is 10-12 weeks. In untreated sheep it may survive and continue to infect for many years. In cattle it is usually less than 1 year.

The prepatent period of ''Fasciola hepatica'' is 10-12 weeks. In untreated sheep it may survive and continue to infect for many years. In cattle it is usually less than 1 year.