Liver fluke (Fasciola Hepatica) is an internal parasite that affects sheep, goats, cattle and other ruminants.
The parasite is often associated with animals that graze in wet and poorly drained areas. It has a significant impact on farmers in many countries and is thought to cost millions annually in lost productivity in the sheep farming industry.
In some countries 20% of all slaughtered carcasses have their livers condemned because of fluke damage.
Although other animals can catch liver fluke it is a particular health problem for sheep and goats, it considered more contagious for these species.
Sheep & Goat Liver Fluke facts:
- It will kill livestock, in large numbers and sometimes without warning.
- If your animals graze on wet boggy pasture, or in marshes, they may be at risk.
- The best way to treat fluke is via prevention and treatment, which are explained below.
Life Cycle of Liver Fluke in Sheep and Goats
Compared to other sheep diseases, liver fluke has a complex life-cycle with various stages of change. It goes through states before it enters a ruminant and starts to cause problems.
The nominal completed life cycle of a fluke is around 17 weeks.
The cycle starts with contaminated livestock faeces that contain the parasites egg. When inside any faeces, the fluke eggs will take around 9 to10 days to hatch.
Once hatched they will turn into their next life stage (called miracidia) where they will seek its intermediate host, the lymnaeid snail.
After hatching, the miracidia have around three hours to infect a lymnaeid snail before dying. At this stage in their life the miracidia cannot survive without water, and they will also struggle to develop if the temperature is below 10°. These are two reasons that fluke is rare during the coldest, or driest, parts of the year.
Once the miracidia are inside the lymnaeid snail, they will reproduce and go through several stages of development. Eventually, around 6-7 weeks, the miracidia emerge from the snails and proceed to encyst vegetation and pasture. Once the parasite is a fluke cyst it is ready to enter its host. The host will ingest the cyst by eating contaminated grass or pasture. Once inside the hosts digestive system, the fluke will start to migrate to the liver where they first start to cause problems.
When inside the hosts liver they will grow and start to tunnel through parts of it, the result is catastrophic liver damage. The liver will become full of tunnels that fill with blood clots and pus, causing it to disintegrate – this process has the nickname liver rot.
Blacks disease is a possibility in unvaccinated sheep infected with liver the fluke. The damage the fluke cause can sometimes result in the emergence of clostridial bacteria. However, black diseases is rare these days owing to the widespread use of clostridial vaccines.
Eventually, the fluke will mature, and move to the bile duct: a few fluke might also make their way to the gall bladder. At this stage in their life the adult fluke will start to lay eggs. These eggs will then be deposited back to the outside world in their hosts faeces. And then the life cycle repeats itself.
To give you an idea how endemic a fluke infection can become, you need to consider that the fluke snails can produce around 100,000 offspring in 3 to 4 months. Each of these snails can host hundreds of fluke each. The problem can quickly build during wet years.
Also, lymnaeid snails can hibernate, remaining dormant till the temperature rises. Making winter and early spring infections possible.
What causes Liver Fluke in Sheep and Goats
Liver fluke will only be a problem for your farm if you have wet land, or your sheep have access to slow steams and boggy areas.
Essentially, liver fluke need warm and wet weather to complete parts of their life cycle, without this wet habitat they will not be able to reproduce. Fluke snails do not like acidic ground, this can help prevent the disease as well.
Wet and warm summers can be a bane for those lands is susceptible to the fluke infestations. Infected snails will reproduce in great numbers at these times, leading to bigger fluke infestations in autumn. If the start of the summer is colder and drier, then the levels of contamination will be much less come autumn.
Lymnaeid snails will hibernate during winter making an infestation possible once they reappear the following year in early spring. If the previous year was bad for fluke, you should expect a severe infestation at the start of the next year.
In years like this it might be best to strategically treat your sheep with a flukicide early in the year if you are expecting a problem – speak with your vet about this so you can pick the best time to treat your animals.
If the previous year’s summer/autumn was warm and dry, you should expect a smaller fluke problem the following year – the snail won’t have a chance to build up their numbers. Therefore; the risk of a bad fluke outbreak the following year should be less, and there might be no need to treat your flock.
Please note: times of infection may vary depending on where you live. That’s why it’s a good idea to talk with vets (or fellow farmers) about your potential fluke problem, and discuss with them the best times to drench your flock to help prevent it.
How does Liver Fluke affect Sheep and Goats?
Fluke infestations can be classed in two ways: acute and chronic infestation.
Acute Liver Fluke (Acute fasciolosis)
Acute fluke infestation will normally occur July-December (this may alter slightly depending on where you live). An acute infestation will consist mostly of immature fluke – these are young fluke that make their home in the liver until they mature.
Once inside the liver they create tunnels that fill with blood clots and pus. The liver will start to disintegrate – this is called Faciolosis or liver rot.
Using fecal egg counts to diagnose a problem at these stage might not indicate anything as the fluke won’t be producing eggs.
Chronic Liver Fluke (Chronic fasciolosis)
Chronic infestations consist of mature and adult fluke infecting the bile duct (and sometimes the gall bladder), but their numbers are smaller compared with acute infestations.
Once mature, the fluke, will start to shed their eggs in the gut. It would now be possible to detect their presence using fecal egg counts.
Usually chronic stages of the infestation are the result of infestations that have happened the previous year, and these infestations will roughly occur between January and April.
Symptoms of Liver Fluke in Sheep, Goats and Lambs
Symptoms vary depending on the age of fluke you are dealing with. Here are some symptoms that you may see in your flock:
Acute Fluke Symptoms
May include: abdominal pain, or anemia, and afflicted animals may appear weak. In extreme cases sheep and lambs may suddenly from haemorrhage – this is more likely to happen when fluke are ingested in high numbers in bad and wet years.
Chronic Fluke Symptoms
May include: progressive weight loss, weakness, anemia and possibly bottle jaw (fluid build up and swelling under the jaw). The lining of the eye may be pale and swollen; this is called flukey eye.
Detection using a faecal egg counts is possible with chronic fluke infestations as the adult fluke will be producing eggs.
Thought needs to be given when treating your flock for liver fluke. There are no set routines when treating the parasite; the number of doses you require – and their timing – will be determined by many elements; these include:
- Previous few months weather – has it been dry or particularly wet.
- Severity of the fluke infestation.
- The time of year – remember, young fluke roughly attack July to December, mature fluke attack January to April (alter these times to suit your local climate and rainy seasons).
Years ago, the only fluke treatments available would kill mature and adult liver fluke. No treatments were available that would treat immature fluke. However; things have changed, newer drugs are available that will treat immature fluke.
All fluke treatments will kill mature flukes, and treat chronic infestations. But when treating immature fluke you need to check your flukicide’s instructions, it may only target immature fluke at a set age. Using it at the wrong time could prove ineffective.
You can buy flukicides that have been combined to provide treatments for other parasites, like roundworm and worms; however, these are considered less efficient than dedicated flukicidal drugs. They might not be suitable choice depending on the severity of the infestation you are dealing with.
Frequency of dosing will vary depending on how bad the year is. Sometimes it’s a good idea to apply a strategic dosing at specific times of the year; this can help to kill off any fluke before any problems occur, and fluke symptoms start to show.
During bad years, many vets will recommend that flocks may need to be vaccinated anything up to 4 times a year. You should consult your vet before using higher dosing amounts like this.
If possible, try to move your sheep on to fresh (and drier) pasture after treating them for fluke, this will help prevent recontamination.
I strongly recommend consulting your local vet when treating liver fluke. There’s a good chance that they will have an idea how serious the problem is in your area. Also, they will be able to instruct you on the correct type of flukicide to use on your flock members.
A few years ago we had a very wet summer, it was one of the wettest on record, and one of the worst years in living memory for liver fluke. During this time many local farmers were i live (Lancashire, UK) were having to drench against fluke ever four weeks during the autumn and early winter – the problem was that bad. Using high doses is not without its risks; the flukicide can kill as many sheep as it saves at these levels of dosing. But not treating them would result in many deaths. It was horrible year.
List of Flukicide Drugs and Treatment
The availability of flukicidal drugs varies depending on which country you live in. Some are available worldwide, others are only available in certain countries.
Below is a list of currently available drugs. I recommend googling them to see whether they are available in your country:
- Triclabendazole (probably the most common and universally available)
Always check the instructions before using any of these drugs on any livestock. Some brands may be designed to be used on a particular breeds, check this out before purchasing.
How to prevent Liver Fluke
When dealing with a fluke problem it is best not to rely on dosing alone. Prevention can go a long way in helping stop the parasite becoming a severe problem. Fluke needs warm and wet areas to complete its life cycle: remove these and you remove the problem.
If possible don’t let your sheep or goats graze on wet, boggy, marshy land. Rotational grazing can help, it may help if you move sheep to drier pasture at certain times in the year.
If possible, fence off wet areas such as streams, bogs, marshes, and other wet areas.
Improving drainage in wet areas can also help.
Deepening streams and creating faster flowing water may help reduce the possible habitat for the lymnaeid snail. Fluke snails do not like fast flowing water or deep water.
Here are a couple of good links about the disease if you want to learn more:
If you are fortunate enough to keep your sheep and goats on land that stays fairly dry most years, liver fluke may never be a problem. Likewise, if your soil is acidic you may never experience a fluke epidemic. Liver fluke is often more a problem in certain areas of a county than others.
If you have land that becomes wet and boggy during rainy seasons, you might want to start planning a drenching program to help with your control of the parasite.
Ask your neighbours if they have to treat for fluke, and talk with your local vet about the threat in your area. This will help you to determine if it’s a problem in your area, and how best to treat it.
In some countries, especially in the UK and Europe, there are dedicated websites and organizations that monitor and predict severity of fluke outbreaks year on year. If an outbreak prediction service like this is available in your area, use it. It may give you an early warning when a bad year is on its way.
The best fluke control is a combined approach using intelligence, local knowledge, prevention, and drug treatments when they are needed. You should modify these as the year and your circumstances seem fit.
What are your thoughts on liver fluke control? Think I’ve missed anything out. Share your thoughts in the comments below. Cheers