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Ovine fasciolosis
Fasciolosis is caused by the liver fluke, a leaf-shaped flatworm that inhabits the liver ducts of ruminants. The sheep is the most sensitive species: it tolerates flukes much less well than the cow and can die from a massive infestation. Th...
What is it?
Fasciolosis is caused by the liver fluke, a leaf-shaped flatworm that inhabits the liver ducts of ruminants.
The sheep is the most sensitive species: it tolerates flukes much less well than the cow and can die from a massive infestation.
The disease is linked to water: the parasite needs a small freshwater snail to complete its cycle. It is therefore found around ponds, springs, ditches, marshy areas and irrigated plots.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Related signs — each one links to its page:
In the acute form, often after a wet season: deep depression, refusal to move, painful stomach, animals found dead without prior signs. It is the young flukes that tear the liver tissue.
In the slow form, the most common: progressive weight loss despite a correct diet, dull and brittle wool, fatigue during exercise.
Pale mucous membranes, reflecting anemia that is setting in.
Soft swelling under the jaw, sometimes stomach distended with fluid.
Decreased appetite and drop in milk production in lactating females.
Yellow coloring of the mucous membranes in some cases, a sign of severe liver damage.
Animals that end up lying down and never get up.
Ewes in poor condition at birth, lambs small and weak.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
Adult flukes live in the liver ducts and lay eggs, which come out with the droppings.
In stagnant water or soggy soil, the eggs hatch and the larval forms enter a small freshwater snail, where they multiply.
The larvae then leave the snail and encyst on blades of grass in wet areas, where they remain infesting for a long time.
The animal swallows them while grazing. The young flukes pass through the wall of the intestine, reach the liver, burrow through it for weeks, then settle in the bile ducts.
Wet years, rainy autumns and irrigated plots increase the number of snails, therefore the risk.
Wet pastures: edges of ponds, springs, ditches, irrigation canals, lowlands which remain soggy.
Rainy years and seasons, periods following floods.
Direct watering in ponds or ditches rather than at the water trough.
Irrigated plots and water leakage areas which create favorable environments for snails.
Young animals, animals in poor condition or malnourished.
Association with other digestive parasites, which worsens the general condition.
Purchase of animals from humid regions without quarantine or examination.
Transmission
Contamination always occurs through grass or plants in wetlands, never through direct contact between animals.
A contaminated plot remains so for a long time, because the encysted forms survive on the vegetation.
Humans can become contaminated, but not by eating sheep meat: only by consuming raw plants that have grown in a humid area frequented by ruminants, such as wild watercress, or by drinking untreated water.
A parasitized liver is discarded at the slaughterhouse: it does not present any danger to the consumer since it is not put up for sale.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The veterinarian relies on the context, in particular the presence of wet areas on the farm, and on the general condition of the herd.
A scat analysis can reveal fluke eggs, but it remains negative throughout the migration phase, that is to say precisely when the acute form is the most dangerous. A negative result therefore does not rule out the disease.
Blood tests, including the search for antibodies and the examination of liver markers, usefully complete the diagnosis.
Examining a dead animal or observing livers seized at the slaughterhouse gives the most direct information: the thickened bile ducts and the flukes themselves are visible. Slaughterhouse returns are a valuable monitoring tool for the breeder.
The veterinarian also evaluates the plot to identify areas at risk.
Treatment
Treatment is based on antiparasitics specific to the fluke, called douvicides. They are not interchangeable: some only act on adult flukes installed in the canals, others also affect young forms migrating into the liver, those which cause serious forms.
It is this difference that makes everything: a product effective on adults will not protect a herd struck by an acute attack. The choice is up to the veterinarian, depending on the season, the form of the disease and the type of production.
Losses of effectiveness are now reported for molecules active against young forms: here too, repeated and systematic treatment of the entire herd accelerates the problem. It is better to treat at the right time, based on diagnosis, than to treat often.
No dose or rhythm should be decided without the veterinarian; ordinary wormers used against roundworms do not act on the fluke.
Weakened animals need sustained nutrition and rest; Liver recovery takes time.
Waiting times for meat and milk are particularly long with douvicides and differ significantly from one product to another; several are prohibited in females producing drinking milk. Ask for these deadlines before any processing.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevent access to wetlands: fence off ponds, springs, the edges of ditches and lowlands, especially in late summer and autumn, the period when infesting forms are most numerous on the grass.
Drain swampy areas where possible, repair leaking water troughs and pipes that create permanent puddles.
Water from the bin rather than from ponds and ditches.
Do not mow fodder in flood-prone areas to provide green fodder.
Monitor slaughterhouse returns: livers systematically seized indicate a problem on the farm.
Quarantine purchased animals and talk to the veterinarian, especially if they come from a humid region.
Reason treatments with the veterinarian according to the season and the analysis results rather than treating on a fixed date.
Possible complications
Death from liver hemorrhage in acute forms, particularly in sheep.
Permanent liver damage, with thickened bile ducts and an animal that never recovers.
Profound anemia and accumulation of fluid in the stomach.
Abortions, sickly lambs, collapse of milk production.
Liver lesions can encourage the awakening of dormant bacteria responsible for severe liver diseases in sheep: this risk justifies discussing the question of vaccination against clostridia with the veterinarian.
Seizure of livers at the slaughterhouse and devalued carcasses.
When to see a veterinarian
Animals slowly lose weight despite a good diet, especially if they graze in wet areas.
An animal has pale mucous membranes or a soft swelling under the jaw.
Sheep die suddenly after a rainy period, without prior signs.
The mucous membranes or the white of the eye take on a yellow tint.
Milk production drops in the herd without any other explanation.
The slaughterhouse informs you of seized livers: ask the veterinarian for advice even if the animals appear healthy.
Transmission to humans
The greater fluke can infect humans, but never through the consumption of sheep or goat meat.
Human contamination occurs by eating raw plants that have grown in a wetland frequented by ruminants, in particular wild watercress and grasses collected along streams, or by drinking untreated water.
In humans, infestation causes fever, pain on the right side of the abdomen and prolonged fatigue. Medical advice is necessary; treatment exists.
The precautions are simple: do not pick or consume raw wild plants growing in grazed wetlands, wash and cook plants of uncertain origin, and drink potable or treated water.
Prognosis
Slow forms treated in time evolve favorably, but the animal takes time to recover and the liver has after-effects.
Acute forms in sheep have a poor prognosis: the animals often die before any treatment.
At the herd level, the result depends above all on the control of wet areas: without intervention on the pasture, the disease returns each season despite treatments.
Frequently asked questions
Is the meat of a sheep affected by fluke dangerous to eat?
No. The fluke lives in the liver, which is discarded and destroyed at the slaughterhouse when it is parasitized. Human contamination does not come through meat but through aquatic plants consumed raw or untreated water.
Does my usual dewormer work on the fluke?
Most often no. The products used against roundworms of the digestive tract have no action on the liver fluke, which is a flatworm and requires specific products. This is a common and costly confusion: ask the vet.
I have a pond on my plot, do I really need to fence it?
This is the most effective measure of all. Without the small freshwater snail that lives in these areas, the parasite cannot complete its cycle. Closing wet spots and watering from the tank breaks the chain much better than any repeated treatment.
Why are my sheep dying even though the dropping analysis was negative?
Because the young flukes which pass through the liver do not yet lay eggs: throughout this phase, the most dangerous in sheep, the dropping analysis remains negative. The veterinarian then relies on the context, blood tests and the examination of a dead animal.
References
FAO — Organisation des Nations unies pour l'alimentation et l'agriculture
OMS — Organisation mondiale de la santé
Content reviewed by the TunisieVet editorial team · Updated 09 August 2026
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