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Adult flukes in the bile ducts shed eggs directly into the ile, which then subsequently enter the intestine. Eggs are then passes out in the faeces of the mammalian host, where they develop anf hatch releasing motile ciliated miracidia. These require 9-10 dyas at optimal temperatures, of around 22-26 degrees. The miracidium have a short life and must locate a suitable snail, the intermediate host, within approximately 3 hours if they are to be effective and continue the life cycle.
Adult flukes in the bile ducts shed eggs directly into the ile, which then subsequently enter the intestine. Eggs are then passes out in the faeces of the mammalian host, where they develop anf hatch releasing motile ciliated miracidia. These require 9-10 dyas at optimal temperatures, of around 22-26 degrees. The miracidium have a short life and must locate a suitable snail, the intermediate host, within approximately 3 hours if they are to be effective and continue the life cycle.
If sucessful, the miracidium will then devlop into sporocysts, then enter the redial stages to the final stages within the intermediate host, which is development into cercaria. These cercaria are then released from the snail, and attach to surfaces such as the tips of grass. Here they encyst and form metacercaria. This represents the infective stage of the lifecycle.
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.
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.