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==Description==
==Description==
Fasciolosis is a condition of ruminants which causes subclinical and clinical disease leading to ill thrift and deaths. The causative organism is the trematode ''[[Fasciola hepatica]]'' which primarily parasitises the bile ducts of sheep and cattle but may occasionally be found in the horse. ''Lymnaea truncatula'', a mud snail, is the intermediate host of ''[[Fasciola hepatica]]'', and transmission of disease is dependent on the presence of appropriate snail habitats. These habitats are more plentiful in areas of high rainfall, such as the western British Isles. However, infected animals may be found outwith these areas due to the transportation of livestock, or unusual weather patterns. The association of fasciolosis with wetter habitats lends a seasonal nature to disease outbreaks, and can help predict the severity of these.
Fasciolosis is a condition of ruminants which causes subclinical and clinical disease leading to ill thrift and deaths. The causative organism is the trematode ''[[Fasciola hepatica]]'' which primarily parasitises the bile ducts of sheep and cattle but may occasionally be found in the horse. ''Lymnaea truncatula'', a mud snail, is the intermediate host of ''[[Fasciola hepatica]]'', and transmission of disease is dependent on the presence of appropriate snail habitats. These habitats are more plentiful in areas of high rainfall, such as the western British Isles. However, infected animals may be found outwith these areas due to the transportation of livestock, or unusual weather patterns. The association of fasciolosis with wetter habitats lends a seasonal nature to disease outbreaks, and can help predict the severity of these.
For instance, wet summers increase both the number of snail habitats and the hatching of fluke eggs, leading to many infected snails. These in turn shed many cercariae, which form a high density of metacercariae on herbage to increase the risk of fasciolosis. Conversely, in dry summers, fewer fluke eggs hatch and snails are restricted to their permanent habitats. Fewer snails become infected and cercariae and metacercariae numbers are low and confined to the areas where snails can survive. The risk of fasciolosis is therefore reduced.
For instance, wet summers increase both the number of snail habitats and the hatching of fluke eggs, leading to many infected snails. These in turn shed many cercariae, which form a high density of metacercariae on herbage to increase the risk of fasciolosis. Conversely, in dry summers, fewer fluke eggs hatch and snails are restricted to their permanent habitats. Fewer snails become infected and cercariae and metacercariae numbers are low and confined to the areas where snails can survive. The risk of fasciolosis is therefore reduced.
[[Image:Fasciola hepatica.jpg|thumb|right|150px|''Fasciola hepatica''. Source: Wikimedia Commons; Author:Adam Cuerden(2007)]]
Upon ingestion, 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, beoming more destructive as they grow to a length of up to one centimetre. In about six weeks, immature fluke enter the bile ducts and mature to adults, where they begin to produce eggs. The prepatent period is around ten to twelve weeks.
Upon ingestion, 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, beoming more destructive as they grow to a length of up to one centimetre. In about six weeks, immature fluke enter the bile ducts and mature to adults, where they begin to produce eggs. The prepatent period is around ten to twelve weeks.