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The severity of the infection is mainly dependent on the number of metacercariae ingested. The Pathogenesis is often described as two-fold. The first stage occuring when the parasite migrates through the liver parenchyma, causing liver damage and haemorrhage. The second phase occurs when the parasite is in the bile ducts, and damage is a result of the haematophagic activity of the adult flukes.
The severity of the infection is mainly dependent on the number of metacercariae ingested. The Pathogenesis is often described as two-fold. The first stage occuring when the parasite migrates through the liver parenchyma, causing liver damage and haemorrhage. The second phase occurs when the parasite is in the bile ducts, and damage is a result of the haematophagic activity of the adult flukes.
===Hosts===
Fasciola hepatica has an indirect life cycle, meaning it has both intermediate and final hosts.
Fasciola hepatica is seen most commonly in sheep, cattle, and goats, but may also be seen in horse, deer, and man.
The most important intermediate host within Europe is the snail of the genus '''Lymnaea'''. The most common, '''Lymnaea truncatula''', which is an amphibious snail found worldwide.
===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.