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''Fasciola Hepatica'' is an hepatic parasite found in mainly in ruminants, namely cows, sheep and goats, but also known to affect horses and pigs.  It is found Worldwide, and within the UK, with its prevalence ever increasing.  It is responsible for a 10-15% production loss in each infected animal, as it affects meat, milk and wool production, so is of huge economic consequence.

''Fasciola Hepatica'' is an hepatic parasite found in mainly in ruminants, namely cows, sheep and goats, but also known to affect horses and pigs.  It is found Worldwide, and within the UK, with its prevalence ever increasing.  It is responsible for a 10-15% production loss in each infected animal, as it affects meat, milk and wool production, so is of huge economic consequence.

''Fasiola Hepatica'' has a definitive ruminant mammalian host and an intermediate molluscian host. Within Europe the intermediate host is almost exclusively the snail 'Lymnaea truncatulata'. The snail habitat is crucial to the survival of the parasite, so wet conditions are favourable to the development and spread of Fasciola hepatica

''Fasiola Hepatica'' has a definitive ruminant mammalian host and an intermediate molluscan host. Within Europe the intermediate host is almost exclusively the snail 'Lymnaea truncatulata'. The snail habitat is crucial to the survival of the parasite, so wet conditions are favourable to the development and spread of Fasciola hepatica

[[Image:Fasciola hepatica.jpg|400px|thumb|right|'''Fasciola hepatica (Copyright Adam Cuerden, Wikimedia Commons) ''']]

[[Image:Fasciola hepatica.jpg|400px|thumb|right|'''Fasciola hepatica (Copyright Adam Cuerden, Wikimedia Commons) ''']]

===Pathogenesis===

===Pathogenesis===

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 occurring 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===

===Hosts===

===Life Cycle===

===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.

Adult flukes in the bile ducts shed eggs directly into the bile, which then subsequently enter the intestine. Eggs are then passes out in the faeces of the mammalian host, where they develop and hatch releasing motile ciliated miracidia.  These require 9-10 days 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.   

If successful, the miracidium will then develop 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.

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

In temperate areas, there are two superimposed epidemiological cycles, known as the summer and winter infections of the snail. On mainland Britain, the summer cycle predominates as a high proportion of snails perish during the winter, but very occasionally, weather sequences allow the winter cycle to affect the pattern of disease. On the west coast of Ireland, the winter cycle of events determines the timing of clinical outbreaks.

In temperate areas, there are two superimposed epidemiological cycles, known as the summer and winter infections of the snail. On mainland Britain, the summer cycle predominates as a high proportion of snails perish during the winter, but very occasionally, weather sequences allow the winter cycle to affect the pattern of disease. On the west coast of Ireland, the winter cycle of events determines the timing of clinical outbreaks.

=== Summer infection of the snail ===

==== Summer infection of the snail ====

Fluke eggs passed in '''spring'''

Fluke eggs passed in '''spring'''

→ immature flukes migrate through liver

→ immature flukes migrate through liver

→ '''acute''' disease '''September-November'''; or '''chronic''' diesease '''January''' onwards

→ '''acute''' disease '''September-November'''; or '''chronic''' disease '''January''' onwards

=== Winter infection of the snail ===

==== Winter infection of the snail ====

Fluke eggs passed in '''late summer'''

Fluke eggs passed in '''late summer'''