Diseases & Solutions
Liver Fluke
Liver fluke (Fasciola hepatica) affects cattle and sheep. Research published in 2015 suggested that 83% of Irish, dairy herds have been exposed to liver fluke. In the UK, similar figures of 72% have been reported in England and 84% in Wales. Based on a 2015 study, a significant outbreak could cost the average, 90-cow Irish dairy herd in the region of €20,000.
From a beef point of view, an infestation can have a negative effect on feed efficiency. This in turn drastically lengthens our finishing period and means we run the risk of missing carcase specifications and receiving a reduced price/kg at sale. UK research suggests an 80-day increased in feeding days where fluke infestation occurs in finishing cattle.
While sheep can suffer chronic, gradual losses in production like those described above, differences in the strength of the immune response (to invading liver fluke) in cattle versus sheep means that death in sheep is relatively common where fluke burdens are high enough.
Liver fluke (Fasciola hepatica) affects cattle and sheep. Research published in 2015 suggested that 83% of Irish, dairy herds have been exposed to liver fluke. In the UK, similar figures of 72% have been reported in England and 84% in Wales. Based on a 2015 study, a significant outbreak could cost the a 90-cow dairy herd in the region of £18,000.
From a beef point of view, an infestation can have a negative effect on feed efficiency. This in turn drastically lengthens our finishing period and means we run the risk of missing carcase specifications and receiving a reduced price/kg at sale. UK research suggests an 80-day increased in feeding days where fluke infestation occurs in finishing cattle.
While sheep can suffer chronic, gradual losses in production like those described above, differences in the strength of the immune response (to invading liver fluke) in cattle versus sheep means that death in sheep is relatively common where fluke burdens are high enough.
The Cycle
The full fluke lice cycle takes 18-20 weeks. When an animal ingests an infective fluke larva (metacercaria), it works its way through digestive system and eventually arrives in the small intestine. Here it develops into an immature liver fluke, before burrowing through the lining of the gut and continuing towards the liver.
The liver plays a vital role for our animal. It is responsible for the removal of harmful toxins from the system, the production of glucose – the body’s fuel source – and the synthesis of important proteins and antibodies which are key components of the immune system.
Young fluke tunnelling through our animal’s liver disrupt these mechanisms. Much like removing the fuel filter from a car engine, a reduction in the organ’s de-toxifying capacity will lead to a build-up of harmful agents in the system. Likewise, reducing the animal’s ability to synthesise glucose and certain proteins leads to production losses – we are in effect producing less fuel for the nutrients we take in. An underperforming liver also leads to an underperforming immune system, opening the door for other ailments. Secondary infection is not uncommon.
One a fluke reaches the bile duct it matures and begins to lay eggs. Here it feeds on blood from the lining of the duct. While a large infestation of mature fluke can lead to anaemia in the animal and have a negative effect on fat digestion, the main losses associated with liver fluke come about during the immature stage of the parasite’s life cycle (first 6-8 weeks) when it is boring tunnels through our animal’s liver. However, with no fluke eggs we have no fluke, so mature or adult liver fluke are just as concerning as immature fluke.
Snails
Liver fluke is an interesting parasite as an intermediate host is required during its development. A mud snail, or water snail, fills this role. These peppercorn-sized snails are most active where there is heat and moisture and will hibernate in cool, dry weather.
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A single mature fluke in an infected animal has the capacity to lay up to 20,000 eggs per day for months on end. When it hits pasture via dung, a fluke egg will hatch into a young larvae (miracidia) with the right levels of moisture and heat. This larva has some level of mobility and goes in search of the intermediate host (mud/water snail) which it needs to complete its life cycle. These mircidia only survive for a few hours outside the snail, but given that a single snail can produce up to 100,000 offspring in three months, if conditions are right the chances of them being present are high.
Inside the snail, the larva multiplies and after 4-6 weeks upwards of 600 infective larvae (cercariae) will be released onto pasture. Once on pasture, these now infective larvae encapsulate/encyst (metacercariae) and in this form are viable on pasture for months. Ingested metacercariae are what leads to a liver fluke infection. It takes around 7-10 days for the ingested larvae excyst in the intestine and become an immature fluke. It is important to note that no flukicide treatment currently available will eradicate encysted fluke larvae.
There is an misconception that all dry farms are ‘immune’ from liver fluke infection given the need for moisture. However, a single wet area can act as a harbour for fluke larvae. Boggy conditions common on heavy farms are ideal, but other favourable scenarios could include depressions in fields, muddy gaps or leaking water troughs. A recent paper published by UCD suggested that temperature was more important as a determinant of fluke risk than moisture.
Fluke risk will be highest in a year where infected animals were grazing pastures during a wet summer (May to July). In this case, symptoms will be expected from July to Autumn. However, encysted larvae are extremely resilient and can remain on pasture for months on end, no symptoms does not mean that an infection is not present and/or spreading. Also, if snails carrying larvae go into hibernation, their release will be delayed until conditions are more favourable. This can lead to sudden symptoms early in the year in a warm, wet spring.
Where there is a fluke problem on a farm, snail habitats need to be identified and either strategically avoided during wet periods, or drained. In terms of treatments, options for sheep and cattle are outlined below. Note not all ingredients are licenced for both species. One option is to remove mature fluke (10-14 weeks) from the system in advance of ‘snail weather’ so that no eggs will be shedding onto risk pastures.
Currently, Triclabendazole (TBZ) is the only active ingredient effective against all stages of liver fluke. Given its comprehensive claim TBZ has been the go-to drug on many farms for a number of years. However, incidences of resistance, particularly in sheep flocks, have been documented in Ireland and the UK.
That said, it is difficult to diagnose TBZ resistance for a number of reasons. In an area with a heavy fluke burden, sheep treated with TBZ could become re-infected rapidly after a treatment – no flukicide has a licenced residual effect. Also, in order to metabolise TBZ a healthy liver is needed. So, if enough damage is already done treating can be a futile exercise. In terms of faecal egg counts, it takes 10-12 weeks after ingestion before we see fluke eggs faeces and resistance to TBZ appears to be more pronounced in non-egg-laying, immature fluke. In order to reduce reliance on TBZ, it is advisable to use products effective against mature fluke in advance of favourable ‘snail weather’.
Faecal coproantigen, serum and milk ELISA analysis can be used to test for the presence of immune responses to liver fluke. Other than ill-thrift and reduction in performance, symptoms of infection in cattle include accumulation of fluid around the jaw (oedema) and anaemia. In sheep, acute fluke causes death as a large burden of immature fluke will overwhelm the liver. The risk of acute fluke (immature fluke in the system) recedes around November-time but is very year-dependent. Chronic fluke infections in sheep can also cause scouring.
Use the solutions below with our FAQ and Best Practice sections to make good decisions on liver fluke control.
The Cycle
The full fluke lice cycle takes 18-20 weeks. When an animal ingests an infective fluke larva (metacercaria), it works its way through digestive system and eventually arrives in the small intestine. Here it develops into an immature liver fluke, before burrowing through the lining of the gut and continuing towards the liver.
The liver plays a vital role for our animal. It is responsible for the removal of harmful toxins from the system, the production of glucose – the body’s fuel source – and the synthesis of important proteins and antibodies which are key components of the immune system.
Young fluke tunnelling through our animal’s liver disrupt these mechanisms. Much like removing the fuel filter from a car engine, a reduction in the organ’s de-toxifying capacity will lead to a build-up of harmful agents in the system. Likewise, reducing the animal’s ability to synthesise glucose and certain proteins leads to production losses – we are in effect producing less fuel for the nutrients we take in. An underperforming liver also leads to an underperforming immune system, opening the door for other ailments. Secondary infection is not uncommon.
One a fluke reaches the bile duct it matures and begins to lay eggs. Here it feeds on blood from the lining of the duct. While a large infestation of mature fluke can lead to anaemia in the animal and have a negative effect on fat digestion, the main losses associated with liver fluke come about during the immature stage of the parasite’s life cycle (first 6-8 weeks) when it is boring tunnels through our animal’s liver. However, with no fluke eggs we have no fluke, so mature or adult liver fluke are just as concerning as immature fluke.
Snails
Liver fluke is an interesting parasite as an intermediate host is required during its development. A mud snail, or water snail, fills this role. These peppercorn-sized snails are most active where there is heat and moisture and will hibernate in cool, dry weather.
A single mature fluke in an infected animal has the capacity to lay up to 20,000 eggs per day for months on end. When it hits pasture via dung, a fluke egg will hatch into a young larvae (miracidia) with the right levels of moisture and heat. This larva has some level of mobility and goes in search of the intermediate host (mud/water snail) which it needs to complete its life cycle. These mircidia only survive for a few hours outside the snail, but given that a single snail can produce up to 100,000 offspring in three months, if conditions are right the chances of them being present are high.
Inside the snail, the larva multiplies and after 4-6 weeks upwards of 600 infective larvae (cercariae) will be released onto pasture. Once on pasture, these now infective larvae encapsulate/encyst (metacercariae) and in this form are viable on pasture for months. Ingested metacercariae are what leads to a liver fluke infection. It takes around 7-10 days for the ingested larvae excyst in the intestine and become an immature fluke. It is important to note that no flukicide treatment currently available will eradicate encysted fluke larvae.
There is an misconception that all dry farms are ‘immune’ from liver fluke infection given the need for moisture. However, a single wet area can act as a harbour for fluke larvae. Boggy conditions common on heavy farms are ideal, but other favourable scenarios could include depressions in fields, muddy gaps or leaking water troughs. A recent paper published by UCD suggested that temperature was more important as a determinant of fluke risk than moisture.
Fluke risk will be highest in a year where infected animals were grazing pastures during a wet summer (May to July). In this case, symptoms will be expected from July to Autumn. However, encysted larvae are extremely resilient and can remain on pasture for months on end, no symptoms does not mean that an infection is not present and/or spreading. Also, if snails carrying larvae go into hibernation, their release will be delayed until conditions are more favourable. This can lead to sudden symptoms early in the year in a warm, wet spring.
Where there is a fluke problem on a farm, snail habitats need to be identified and either strategically avoided during wet periods, or drained. In terms of treatments, options for sheep and cattle are outlined below. Note not all ingredients are licenced for both species and rafoxanide is not currently licenced for sale in the UK. One option is to remove mature fluke (10-14 weeks) from the system in advance of ‘snail weather’ so that no eggs will be shedding onto risk pastures.
Currently, Triclabendazole (TBZ) is the only active ingredient effective against all stages of liver fluke. Given its comprehensive claim TBZ has been the go-to drug on many farms for a number of years. However, incidences of resistance, particularly in sheep flocks, have been documented in Ireland and the UK.
That said, it is difficult to diagnose TBZ resistance for a number of reasons. In an area with a heavy fluke burden, sheep treated with TBZ could become re-infected rapidly after a treatment – no flukicide has a licenced residual effect. Also, in order to metabolise TBZ a healthy liver is needed. So, if enough damage is already done treating can be a futile exercise. In terms of faecal egg counts, it takes 10-12 weeks after ingestion before we see fluke eggs faeces and resistance to TBZ appears to be more pronounced in non-egg-laying, immature fluke. In order to reduce reliance on TBZ, it is advisable to use products effective against mature fluke in advance of favourable ‘snail weather’.
Faecal coproantigen, serum and milk ELISA analysis can be used to test for the presence of immune responses to liver fluke. Other than ill-thrift and reduction in performance, symptoms of infection in cattle include accumulation of fluid around the jaw (oedema) and anaemia. In sheep, acute fluke causes death as a large burden of immature fluke will overwhelm the liver. The risk of acute fluke (immature fluke in the system) recedes around November-time but is very year-dependent. Chronic fluke infections in sheep can also cause scouring.
Use the solutions below with our FAQ and Best Practice sections to make good decisions on liver fluke control.
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