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Acute and subacute liver fluke (fascioliasis) in lambs – clinical signs and diagnosis
Acute and sub-acute liver fluke (fascioliasis) in lambs – clinical signs and diagnosis
- What is the impact and clinical signs of acute fluke in lambs
- Is my farm at risk?
- How do I diagnose acute/sub-acute fluke in my lambs?
Liver fluke, caused by Fasciola hepatica, is a significant disease affecting all ages of sheep and cattle in the UK. Fluke infection is estimated to cost the UK agriculture industry as a whole, about £300 million a year1, and more specifically in sheep production losses of at least £3-5 per ewe per year.2
Liver fluke can affect lambs from their first summer grazing if the weather conditions are suitable. This can mean lambs can be infected and become clinically ill or have livers condemned when slaughtered at the end of the summer/autumn. Milder winters in the UK, along with wet summers, increase the risk of liver fluke infections and disease.
What is the impact and clinical signs of acute fluke in lambs?
Disease due to liver fluke in sheep can be categorised into 3 types of disease:
1. Acute – this type of disease can be seen between July and September in all classes of stock and is caused by thousands of immature flukes migrating from the intestines and through the liver, where they can cause massive liver damage. Animals affected either die suddenly or become pale (anaemic), have a painful and/or swollen abdomen due to accumulation of fluid. This is likely to be the most common type of disease seen in lambs if they have been grazing high risk pasture, and the weather has been favourable over early summer.
2. Sub-acute – can affect lambs and adults between October and January. This type of disease is caused by a mixture of migrating immature and adult fluke. Affected animals will become dull and suddenly lose weight and condition. Animal may display the classic ‘bottle jaw’ swelling under the chin, or distended abdomen due to ascites.
3. Chronic – more on this in ‘Chronic fluke in sheep – clinical signs and diagnosis .’
The biggest impact in fattening lambs will be due to acute and sub acute disease in late summer/autumn. Weight loss, loss in condition, lamb deaths and abattoir condemnations of livers will all contribute to the economic losses due to liver fluke. Treatment costs and meat withhold after treatment delaying marketing of other lambs in the group who need treating may also have an impact financially. As well as the financial impact, sheep that are affected can be experiencing pain and discomfort due to the disease, negatively impacting health and welfare.
Is my farm at risk?
The life cycle of liver fluke is relatively complicated and involves an intermediate host, the mud snail, which is essential for the fluke to complete their life cycle.
In basic terms, the adult liver fluke lay eggs which are passed in the faeces of infected sheep and onto pasture. Under the correct conditions (temperatures of >10°C), the eggs on the pasture hatch into the first larval stage of the fluke, which seek out the mud snail where they undergo a further 2 stages of development. When the climate is suitable (wet and mild), these infective larvae attach themselves to wet grass and other herbage, where they wait to be eaten by the grazing sheep/cattle. Onceingested, the final stage of the life cycle is completed as the larvae penetrate the intestinal wall and migrate through the liver to the bile ducts.
The life cycle is relatively long. The mud snail stage of the cycle takes a few weeks to a few months, depending on temperature and weather. The immature liver fluke take a further 10-12 weeks to migrate to the bile duct and develop to egg-laying adults once inside the sheep.
Whether your farm is at risk of liver fluke or not will depend on two main factors:
1. Are there any areas of the farm that are suitable for the mud snail to live (intermediate host, essential for liver fluke infection – see life cycle below) i.e. wet and muddy, undrained areas
2. Is there fluke present on the farm and in the mud snails.
Historically, farms in wetter areas of the country would be more severely affected by liver fluke. Milder winters, which are becoming more common in the UK due to changes in climate patterns, as well as wetter summers will increase the risk of disease due to liver fluke across the country.
How do I diagnose acute/sub-acute fluke in my lambs?
Diagnosis of liver fluke in lambs can be challenging. Liver fluke egg detection in lamb’s faeces is not a suitable method for diagnosis of acute or sub-acute fluke due to the long (10-12 week) development phase from ingestion to egg-laying adults.
Acute and sub-acute fluke can be diagnosed by performing postmortem examination of any dead lambs, assessing clinical signs seen in the group of animals, along with the flock history and risk due to weather. Blood samples to detect fluke antibodies can be very useful from summer onwards, as antibodies can be detected 2-4 weeks after infection.
If your lambs are sent dead weight straight to the abattoir,always take notice and discuss kill sheets/reports with your vet if there have been any liver condemnations. Liver condemnations may be due to liver fluke damage and can be a good indication of the liver fluke status in your lambs.
References:
1. https://ahdb.org.uk/liver-fluke
2. https://livrepository.liverpool.ac.uk/3103889/1/181219%20In%20Practice%20Liver%20fluke%20in%20sheep.docx
Acute and sub-acute liver fluke (fascioliasis) in lambs – clinical signs and diagnosis
- What is the impact and clinical signs of acute fluke in lambs
- Is my farm at risk?
- How do I diagnose acute/sub-acute fluke in my lambs?
Liver fluke, caused by Fasciola hepatica, is a significant disease affecting all ages of sheep and cattle in the UK. Fluke infection is estimated to cost the UK agriculture industry as a whole, about £300 million a year1, and more specifically in sheep production losses of at least £3-5 per ewe per year.2
Liver fluke can affect lambs from their first summer grazing if the weather conditions are suitable. This can mean lambs can be infected and become clinically ill or have livers condemned when slaughtered at the end of the summer/autumn. Milder winters in the UK, along with wet summers, increase the risk of liver fluke infections and disease.
What is the impact and clinical signs of acute fluke in lambs?
Disease due to liver fluke in sheep can be categorised into 3 types of disease:
1. Acute – this type of disease can be seen between July and September in all classes of stock and is caused by thousands of immature flukes migrating from the intestines and through the liver, where they can cause massive liver damage. Animals affected either die suddenly or become pale (anaemic), have a painful and/or swollen abdomen due to accumulation of fluid. This is likely to be the most common type of disease seen in lambs if they have been grazing high risk pasture, and the weather has been favourable over early summer.
2. Sub-acute – can affect lambs and adults between October and January. This type of disease is caused by a mixture of migrating immature and adult fluke. Affected animals will become dull and suddenly lose weight and condition. Animal may display the classic ‘bottle jaw’ swelling under the chin, or distended abdomen due to ascites.
3. Chronic – more on this in ‘Chronic fluke in sheep – clinical signs and diagnosis .’
The biggest impact in fattening lambs will be due to acute and sub acute disease in late summer/autumn. Weight loss, loss in condition, lamb deaths and abattoir condemnations of livers will all contribute to the economic losses due to liver fluke. Treatment costs and meat withhold after treatment delaying marketing of other lambs in the group who need treating may also have an impact financially. As well as the financial impact, sheep that are affected can be experiencing pain and discomfort due to the disease, negatively impacting health and welfare.
Is my farm at risk?
The life cycle of liver fluke is relatively complicated and involves an intermediate host, the mud snail, which is essential for the fluke to complete their life cycle.
In basic terms, the adult liver fluke lay eggs which are passed in the faeces of infected sheep and onto pasture. Under the correct conditions (temperatures of >10°C), the eggs on the pasture hatch into the first larval stage of the fluke, which seek out the mud snail where they undergo a further 2 stages of development. When the climate is suitable (wet and mild), these infective larvae attach themselves to wet grass and other herbage, where they wait to be eaten by the grazing sheep/cattle. Onceingested, the final stage of the life cycle is completed as the larvae penetrate the intestinal wall and migrate through the liver to the bile ducts.
The life cycle is relatively long. The mud snail stage of the cycle takes a few weeks to a few months, depending on temperature and weather. The immature liver fluke take a further 10-12 weeks to migrate to the bile duct and develop to egg-laying adults once inside the sheep.
Whether your farm is at risk of liver fluke or not will depend on two main factors:
1. Are there any areas of the farm that are suitable for the mud snail to live (intermediate host, essential for liver fluke infection – see life cycle below) i.e. wet and muddy, undrained areas
2. Is there fluke present on the farm and in the mud snails.
Historically, farms in wetter areas of the country would be more severely affected by liver fluke. Milder winters, which are becoming more common in the UK due to changes in climate patterns, as well as wetter summers will increase the risk of disease due to liver fluke across the country.
How do I diagnose acute/sub-acute fluke in my lambs?
Diagnosis of liver fluke in lambs can be challenging. Liver fluke egg detection in lamb’s faeces is not a suitable method for diagnosis of acute or sub-acute fluke due to the long (10-12 week) development phase from ingestion to egg-laying adults.
Acute and sub-acute fluke can be diagnosed by performing postmortem examination of any dead lambs, assessing clinical signs seen in the group of animals, along with the flock history and risk due to weather. Blood samples to detect fluke antibodies can be very useful from summer onwards, as antibodies can be detected 2-4 weeks after infection.
If your lambs are sent dead weight straight to the abattoir,always take notice and discuss kill sheets/reports with your vet if there have been any liver condemnations. Liver condemnations may be due to liver fluke damage and can be a good indication of the liver fluke status in your lambs.
References:
1. https://ahdb.org.uk/liver-fluke
2. https://livrepository.liverpool.ac.uk/3103889/1/181219%20In%20Practice%20Liver%20fluke%20in%20sheep.docx