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Fasciolosis
Fasciolosis is caused by a flatworm, the fluke, which settles in the liver and bile ducts of cattle. It is caught by grazing in wet areas: the edges of ponds, ditches, marshy lands, around irrigation canals and wadis. The parasite needs a s...
What is it?
Fasciolosis is caused by a flatworm, the fluke, which settles in the liver and bile ducts of cattle.
It is caught by grazing in wet areas: the edges of ponds, ditches, marshy lands, around irrigation canals and wadis. The parasite needs a small freshwater snail to complete its cycle, and this snail only lives in these wet environments.
In cattle, the disease is most often silent and progressive: no sudden death, but animals which produce less, gain weight poorly and reproduce less well.
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:
Slow weight loss despite a correct diet, or a condition that does not improve despite a good ration.
Dull, stitched coat, animal that does not look “finished”.
Decrease in milk production and lengthening of calving intervals.
Anemia: pale mucous membranes of the eyes and gums.
Edema under the jaw, in the form of a soft pocket, in significant infestations.
Intermittent diarrhea or loose droppings.
Growth retardation in young cattle.
In massive infestations, animals may stay away, tired, with no other obvious signs.
Many infested animals show no visible signs: only the production report or the examination of the livers at the slaughterhouse reveals this.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
The parasite is a flatworm, the liver fluke, which lives as an adult in the bile ducts.
Its cycle necessarily passes through a small freshwater snail living in humid areas. Without this snail, no contamination.
The infesting forms encyst on grass and plants in wet areas, where cattle swallow them while grazing.
The young flukes pass through the liver before reaching the bile ducts: this path damages the liver tissue and leaves permanent scars.
Pastures crossed by a wadi, an irrigation canal, a ditch, or including a pond or marshy area.
Free access for animals to natural water points for drinking.
Rainy periods and years, and irrigated plots.
Grazing low-lying areas at the end of summer and autumn, when animals look for green in damp hollows.
Young cattle in the first grazing season and cows at the start of lactation, more vulnerable to the consequences.
Sharing damp plots with sheep or goats, which also carry the parasite.
Transmission
Cattle become contaminated by grazing on grass in wetlands or by drinking stagnant water from ponds, ditches and canals.
Hay or grass cut in damp plots can also be contaminating.
There is no direct transmission from one cattle to another, neither through contact nor through milk.
Rainy years and seasons clearly increase the risk, as does irrigation which creates permanent wet areas.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The diagnosis cannot be made by eye: talk to the veterinarian as soon as animals lose weight without explanation or if production drops in the flock.
A laboratory analysis of dung looks for the eggs of the parasite. It is only positive when the flukes are adults: a negative result does not exclude a recent infestation.
Blood tests, including on tank milk on dairy farms, make it possible to identify infested herds.
The findings made at the slaughterhouse (livers seized) are valuable information: ask for them and send them to the veterinarian.
A blood test can assess anemia and the impact on the liver.
Treatment
Antiparasitics active on the fluke exist; their choice and the moment of their use are the responsibility of the veterinarian.
Not all of them are active on the same stages of the parasite: treating at the wrong time of year often means doing nothing, while selecting resistant flukes.
The timing of treatment is based on the parasite cycle, the season and grazing management, not on habit.
Cases of resistance to antiparasitics active on the fluke have been described: systematic and repeated treatment of the herd, without diagnosis, accelerates this phenomenon.
Special attention for lactating cows: not all products can be used and waiting times for milk and meat must be scrupulously respected. Only the prescribing veterinarian can tell you these.
Treatment alone does not solve anything if the animals return to the same wet plot: it must always be accompanied by action on the pasture.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention depends on pasture management much more than on medications.
Fence or exclude wet areas: edges of ponds, ditches, swamps, edges of irrigation canals.
Drain what can be drained, fill in permanent puddles, repair leaking water troughs that create muddy areas.
Have animals drink from a trough rather than from ponds, ditches or wadis.
Avoid mowing fodder in the wettest plots, or allow it to dry for a long time before distribution.
Adapt the rotation of plots: reserve risk areas for the least dangerous periods, and keep young cattle on healthy plots.
Quarantine and have purchased animals examined before mixing them with the herd.
Discuss the management plan with your veterinarian every year: fluke is a plot problem, it is handled at farm level.
Possible complications
Permanently damaged liver, with thickened bile ducts and scars that do not disappear.
Seizure of livers at the slaughterhouse and loss of value of the carcass.
Anemia and weight loss in heavily infested animals.
Reduced fertility, extended calving intervals, slowed growth in young.
Increased susceptibility to other diseases, the liver being a key organ in the animal's defenses.
Very massive infestations can lead to death, more rarely in cattle than in sheep.
When to see a veterinarian
Animals lose weight or do not gain weight even though the ration is correct.
The milk production of the lot drops without obvious cause.
You observe a soft pocket under the jaw of one or more animals.
The mucous membranes are pale, the hair is dull, the young grow poorly.
Livers of your animals have been seized at the slaughterhouse.
Your plots have wet areas and you have never taken stock of the moat with your veterinarian.
Transmission to humans
Humans can also be affected by fluke, but never through contact with a sick animal or through consumption of meat or milk.
Human contamination occurs by eating raw plants that have grown in water or humid areas, such as watercress, or by drinking untreated water from these areas.
Wash plants eaten raw carefully, do not pick wild plants in marshy areas frequented by livestock, and only drink potable water.
In case of stomach pain, prolonged fever or unexplained fatigue after this type of exposure, consult a doctor and inform him of the agricultural context.
Prognosis
Well taken care of, the herd returns to its production level, but this takes time.
Liver lesions already present cannot be completely repaired: hence the importance of acting before they accumulate.
Without action on damp plots, reinfestation is certain and the problem returns every year.
Farms that combine grazing management and reasonable treatments see liver seizures decrease significantly.
Frequently asked questions
My cows don't look sick: can I still have fluke on my farm?
Yes, this is even the most common case in cattle. The parasite acts silently: less milk, slower growth, reduced fertility. Livers seized at the slaughterhouse and laboratory analyzes are often the only clues.
Can I get fluke from drinking milk or eating meat from my animals?
No. Human contamination occurs by eating raw plants that have grown in water, such as watercress, or by drinking non-potable water from wetlands. Milk and meat do not transmit the parasite.
Is it enough to treat the entire herd once a year?
No. If the animals return to the same wetlands, they immediately become reinfested. And treating systematically, without diagnosis or good timing, promotes the appearance of resistant flukes. The plan is built with the veterinarian, plot by plot.
Should I dry out all my plots?
This is neither possible nor always desirable. The main thing is to prevent animals from accessing the wettest areas at the riskiest time, and to give them water from the water trough rather than from the pond.
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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