PC Sheep Liver Fluke2020 FINAL


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Introduction Liver fluke (Fasciola hepatica) are flatworm parasites which commonly infect grass-fed cattle and sheep in Ireland but can also infect other grazing animals. Recent survey data has suggested that >60% of Irish sheep flocks will have liver fluke infections, with farms on wet lowland pastures being most susceptible. However, due to the favourable climate, almost all sheep farms in Ireland are at risk of infection. Disease caused by liver fluke (fasciolosis) can result in serious clinical signs and high levels of mortality in severe infections. Liver fluke infections in both sheep and cattle are responsible for significant economic losses to the Irish industry. Liver fluke is therefore an important concern for sheep farmers. Liver fluke infections can cause losses in different ways: • On farm, liver fluke can cause either acute, subacute or chronic disease in sheep. Acute disease is the most alarming as it can cause rapid death in a large proportion of affected sheep. Subacute or chronic disease may also be serious and cause significant production losses. • Low levels of liver fluke infection can cause general ill-thrift and significantly reduce growth rates, wool production, lambing percentages and ewe milk production. • The livers of animals which are, or have previously been, infected with liver fluke will be condemned at slaughter as not fit for human consumption. The liver fluke life cycle Sheep and lambs become infected by eating grass contaminated with the encapsulated infective larvae of the liver fluke parasite, known as metacercariae. In the intestine, the larvae (immature flukes) are released from their cysts, cross the intestinal wall and move into the liver. They typically spend 8-12 weeks moving through the liver and causing considerable tissue damage. The immature flukes finally reach the bile ducts where they continue to grow and develop into mature adults, feeding on the sheep’s blood and producing thousands of eggs each day. The eggs are carried in the bile into the small intestine from where they are passed out in the faeces and reach the pasture. Once the eggs are on pasture, exposure to sunlight (increased environmental temperature) and moisture trigger the eggs to hatch, and a small larval stage (the miracidium) emerges. These larvae must find and penetrate a snail (the so-called liver fluke snail or mud snail) which are found in wet or ‘flukey’ areas on individual farms. In the snail the larvae develop through the sporocyst and redia stages before roughly 500-1000 of the final larval stage (cercaria) emerge from the snail and settle on grass as encapsulated infective larvae (metacercariae) ready to be consumed again. Without appropriate treatment, adult liver fluke can survive in sheep for many years.

Immature fluke migrate to liver Develops into adult fluke

Eggs passed in faeces

Metacercariae are ingested by cattle, sheep and other hosts

Cercariae encyst on grass forming metacercariae

Miracidia released

Cercariae leave snail

Miracidia invade snail (intermediate host) develops and multiplies as a sporocyst


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