Chronic Liver Fluke in sheep – treatment and prevention
- Why is it important that I monitor my flock for fluke?
- When should I treat chronic fluke?
- What can I use to treat chronic fluke?
- How can I prevent chronic fluke on my farm?
Chronic fluke in sheep is a disease which occurs due to persistent infection with liver fluke, causing long-term damage to the liver. See ‘Chronic liver fluke – clinical signs and diagnosis’ for more information on identifying at-risk farms and how to diagnose chronic fluke.
Why is it important that I monitor my flock for fluke?
Sheep which are affected with chronic fluke may show weight loss, diarrhoea, and/or a fluid swelling under the jaw (‘bottle-jaw’). As chronic fluke tends to affect sheep in late winter/early spring, many affected ewes will be pregnant at this time. This weight loss and energy depletion in heavily pregnant ewes can lead to pregnancy toxaemia (‘twin lamb disease’), abortion and even death of the ewe. This makes it vital to monitor for chronic fluke during winter and spring to allow any affected animals to be diagnosed and treated rapidly, without having an impact on their pregnancy and their welfare.
Another reason to keep monitoring each year is the impact of climate change – warmer, wetter winters improve fluke survival and increase the risk of sheep (and cattle) picking up fluke. The consensus from climate change studies is that fluke prevalence is likely to increase, and that the timing of outbreaks will become less predictable – meaning we need to find ways to prevent the disease rather than relying on blanket treatment.1 Fluke can also be bought in via purchased sheep or cattle and then spread onto pasture in faeces, so even farms which have not previously seen fluke may be affected in future if the warmer, wetter weather conditions make the farmland suitable for mud snails.
When should I treat chronic fluke?
For farms which have never had liver fluke problems
You can screen for evidence of exposure to the fluke parasite. A proportion of the group can be blood tested for fluke antibodies, which are only produced after exposure to liver fluke. Positive results mean that fluke is present on the farm and should be taken into account when health planning with your vet, as monitoring for disease will be required. If the flock buys in ewes, then lambs at least a month into their first grazing season are usually the best animals to check for fluke exposure as they can only have been exposed on the home farm and any exposure will have been recent.
For at risk farms
Fluke can be diagnosed by taking pooled faecal samples from at risk groups. Doing this frequently can identify fluke burdens before they have a chance to cause significant liver damage across the group. It is usually recommended to test faecal samples for fluke coproantigen in late autumn as this can detect fluke burdens a few weeks earlier than looking for fluke eggs; meaning infected animals can be treated sooner and there is less risk of chronic fluke developing later in the season. This test is more expensive and may need to be done on individual samples rather than pooled samples. From mid-winter onwards most fluke inside the sheep will be producing eggs so testing faeces for the presence of fluke eggs is cheap and effective for monitoring for chronic fluke if done repeatedly. Individual parasites will shed fluke eggs intermittently, so the numbers of eggs found cannot be used to give an accurate idea of fluke burden – instead the sample is classified ‘positive’ if fluke eggs are found.
Whichever faecal test is used, if there are no clinical signs of fluke within the flock and no evidence of active fluke in abattoir reports then it is usually recommended that routine faecal screening is done every 4-8 weeks.2 If faecal tests show positive results then your vet can recommend suitable options for treatment and when monitoring should be resumed. They may also recommend post-treatment faecal sampling to ensure that the fluke treatment was effective and that there is no resistance present – see the SCOPS website for more details on flukicide resistance.3
What can I use to treat chronic fluke?
Treatment of chronic fluke involves killing adult fluke. There are several drugs available which are effective against adult fluke – this is a stark difference compared to treating acute or subacute fluke, where currently only triclabendazole-containing products are effective.
As such, we recommend reserving triclabendazole products for treatment of acute and subacute liver fluke only, usually in autumn or early winter, and using other options to treat chronic fluke in late winter onwards. The table below shows various options for treating chronic fluke:
As discussed in ‘Acute/subacute fluke - treatment and prevention’, there is widespread triclabendazole resistance reported in liver fluke in the UK.4
There have been no reports of resistance to the other active ingredients listed above in the UK. For this reason, it is recommended that triclabendazole is reserved for targeted treatment of acute and subacute fluke, as this is the only effective treatment for early immature liver fluke.
Following confirmation of infection via one of the diagnostic methods discussed above, chronic liver fluke should be treated with one of the adulticides above (closantel, albendazole or oxyclozanide).
How can I prevent chronic fluke on my farm?
Preventing liver fluke on your farm may be challenging if the parasite is already present. The first step to dealing with liver fluke is to make the most of the diagnostic tools available to determine the level of infection on your farm. Blood sampling homebred lambs from late summer onwards will indicate when animals are becoming infected in the autumn. Using this, along with parasite forecasting tools will help predict when your flock will need treating. Using triclabendazole exclusively to target acute fluke in the autumn and early winter will help reduce the chances of triclabendazole resistance developing.
If liver fluke is present on your farm, you should talk to your vet about testing for triclabendazole resistance in your flock. This knowledge will allow you to formulate the most effective liver fluke treatment plan for your farm. Treatment with one of the adult/late immature flukicides (e.g. closantel/oxyclosanide/albendazole) in late winter/early spring will ensure that any triclabendazole resistant fluke still present in your sheep will be killed and pasture contamination will be reduced for the subsequent season.
Avoiding grazing heavily contaminated pastures (known ‘flukey’ ground) in the autumn, will help reduce the infection levels in your sheep. Avoiding snail habitat is very difficult in reality, but improving pasture and fencing off very wet, muddy areas may help in liver fluke prevention. Effectively treating other livestock e.g. cattle, on your farm will also reduce the level of disease present.
If liver fluke is not a big concern on your farm, it is imperative that you do not buy fluke in with new stock. Follow SCOPS guidelines on quarantine testing and treatment to avoid bringing fluke onto your farm.5
References:
1. Williams DJL. An update on liver fluke in sheep. Pract In 2020.
2. https://www.scops.org.uk/workspace/pdfs/fluke-diagnostics-treatment-poster_1.pdf
3. https://www.scops.org.uk/internal-parasites/liver-fluke/tackling-resistance/
4. Kamaludeen J, Graham-Brown J, Stephens N, Miller J, Howell A, Beesley NJ, Hodgkinson J, Learmount J, Williams D. Lack of efficacy of triclabendazole against Fasciola hepatica is present on sheep farms in three regions of England, and Wales. Vet Rec. 2019 Apr 20;184(16):502. doi: 10.1136/vr.105209. Epub 2019 Mar 1. PMID: 30824600; PMCID: PMC6583106.
5. Quarantine Treatments | Liver Fluke | SCOPS
Chronic Liver Fluke in sheep – treatment and prevention
- Why is it important that I monitor my flock for fluke?
- When should I treat chronic fluke?
- What can I use to treat chronic fluke?
- How can I prevent chronic fluke on my farm?
Chronic fluke in sheep is a disease which occurs due to persistent infection with liver fluke, causing long-term damage to the liver. See ‘Chronic liver fluke – clinical signs and diagnosis’ for more information on identifying at-risk farms and how to diagnose chronic fluke.
Why is it important that I monitor my flock for fluke?
Sheep which are affected with chronic fluke may show weight loss, diarrhoea, and/or a fluid swelling under the jaw (‘bottle-jaw’). As chronic fluke tends to affect sheep in late winter/early spring, many affected ewes will be pregnant at this time. This weight loss and energy depletion in heavily pregnant ewes can lead to pregnancy toxaemia (‘twin lamb disease’), abortion and even death of the ewe. This makes it vital to monitor for chronic fluke during winter and spring to allow any affected animals to be diagnosed and treated rapidly, without having an impact on their pregnancy and their welfare.
Another reason to keep monitoring each year is the impact of climate change – warmer, wetter winters improve fluke survival and increase the risk of sheep (and cattle) picking up fluke. The consensus from climate change studies is that fluke prevalence is likely to increase, and that the timing of outbreaks will become less predictable – meaning we need to find ways to prevent the disease rather than relying on blanket treatment.1 Fluke can also be bought in via purchased sheep or cattle and then spread onto pasture in faeces, so even farms which have not previously seen fluke may be affected in future if the warmer, wetter weather conditions make the farmland suitable for mud snails.
When should I treat chronic fluke?
For farms which have never had liver fluke problems
You can screen for evidence of exposure to the fluke parasite. A proportion of the group can be blood tested for fluke antibodies, which are only produced after exposure to liver fluke. Positive results mean that fluke is present on the farm and should be taken into account when health planning with your vet, as monitoring for disease will be required. If the flock buys in ewes, then lambs at least a month into their first grazing season are usually the best animals to check for fluke exposure as they can only have been exposed on the home farm and any exposure will have been recent.
For at risk farms
Fluke can be diagnosed by taking pooled faecal samples from at risk groups. Doing this frequently can identify fluke burdens before they have a chance to cause significant liver damage across the group. It is usually recommended to test faecal samples for fluke coproantigen in late autumn as this can detect fluke burdens a few weeks earlier than looking for fluke eggs; meaning infected animals can be treated sooner and there is less risk of chronic fluke developing later in the season. This test is more expensive and may need to be done on individual samples rather than pooled samples. From mid-winter onwards most fluke inside the sheep will be producing eggs so testing faeces for the presence of fluke eggs is cheap and effective for monitoring for chronic fluke if done repeatedly. Individual parasites will shed fluke eggs intermittently, so the numbers of eggs found cannot be used to give an accurate idea of fluke burden – instead the sample is classified ‘positive’ if fluke eggs are found.
Whichever faecal test is used, if there are no clinical signs of fluke within the flock and no evidence of active fluke in abattoir reports then it is usually recommended that routine faecal screening is done every 4-8 weeks.2 If faecal tests show positive results then your vet can recommend suitable options for treatment and when monitoring should be resumed. They may also recommend post-treatment faecal sampling to ensure that the fluke treatment was effective and that there is no resistance present – see the SCOPS website for more details on flukicide resistance.3
What can I use to treat chronic fluke?
Treatment of chronic fluke involves killing adult fluke. There are several drugs available which are effective against adult fluke – this is a stark difference compared to treating acute or subacute fluke, where currently only triclabendazole-containing products are effective.
As such, we recommend reserving triclabendazole products for treatment of acute and subacute liver fluke only, usually in autumn or early winter, and using other options to treat chronic fluke in late winter onwards. The table below shows various options for treating chronic fluke:
As discussed in ‘Acute/subacute fluke - treatment and prevention’, there is widespread triclabendazole resistance reported in liver fluke in the UK.4
There have been no reports of resistance to the other active ingredients listed above in the UK. For this reason, it is recommended that triclabendazole is reserved for targeted treatment of acute and subacute fluke, as this is the only effective treatment for early immature liver fluke.
Following confirmation of infection via one of the diagnostic methods discussed above, chronic liver fluke should be treated with one of the adulticides above (closantel, albendazole or oxyclozanide).
How can I prevent chronic fluke on my farm?
Preventing liver fluke on your farm may be challenging if the parasite is already present. The first step to dealing with liver fluke is to make the most of the diagnostic tools available to determine the level of infection on your farm. Blood sampling homebred lambs from late summer onwards will indicate when animals are becoming infected in the autumn. Using this, along with parasite forecasting tools will help predict when your flock will need treating. Using triclabendazole exclusively to target acute fluke in the autumn and early winter will help reduce the chances of triclabendazole resistance developing.
If liver fluke is present on your farm, you should talk to your vet about testing for triclabendazole resistance in your flock. This knowledge will allow you to formulate the most effective liver fluke treatment plan for your farm. Treatment with one of the adult/late immature flukicides (e.g. closantel/oxyclosanide/albendazole) in late winter/early spring will ensure that any triclabendazole resistant fluke still present in your sheep will be killed and pasture contamination will be reduced for the subsequent season.
Avoiding grazing heavily contaminated pastures (known ‘flukey’ ground) in the autumn, will help reduce the infection levels in your sheep. Avoiding snail habitat is very difficult in reality, but improving pasture and fencing off very wet, muddy areas may help in liver fluke prevention. Effectively treating other livestock e.g. cattle, on your farm will also reduce the level of disease present.
If liver fluke is not a big concern on your farm, it is imperative that you do not buy fluke in with new stock. Follow SCOPS guidelines on quarantine testing and treatment to avoid bringing fluke onto your farm.5
References:
1. Williams DJL. An update on liver fluke in sheep. Pract In 2020.
2. https://www.scops.org.uk/workspace/pdfs/fluke-diagnostics-treatment-poster_1.pdf
3. https://www.scops.org.uk/internal-parasites/liver-fluke/tackling-resistance/
4. Kamaludeen J, Graham-Brown J, Stephens N, Miller J, Howell A, Beesley NJ, Hodgkinson J, Learmount J, Williams D. Lack of efficacy of triclabendazole against Fasciola hepatica is present on sheep farms in three regions of England, and Wales. Vet Rec. 2019 Apr 20;184(16):502. doi: 10.1136/vr.105209. Epub 2019 Mar 1. PMID: 30824600; PMCID: PMC6583106.
5. Quarantine Treatments | Liver Fluke | SCOPS