Liver fluke infections have become increasingly common in horses in recent years. As with other worms, animals become infected while grazing. The liver fluke has a complicated, indirect life cycle. A freshwater snail is required as an intermediate host. Because these snails survive only in moist environments, liver fluke infections are generally limited to horses grazing on wet, damp pastures. Infections are even more common on pastures where sheep or cattle have grazed in the previous year. Liver fluke is not naturally present on high sandy soils or well-drained pastures. However, the risk of infection is always present in western pasture areas, for example. Keep in mind that even a single damp corner or ditch with water can be a source of liver fluke infection.
The adult liver fluke lives in the bile ducts of the liver and produces characteristic eggs, which are excreted with the manure. Depending on the environmental temperature and the presence of water, a larva develops within 3 weeks, swimming in the water and actively seeking the intermediate host: a freshwater snail. The larva penetrates the snail and multiplies inside. There it develops into the next stage, known as cercariae. These cercariae leave the snail and become infectious for the horse, now called metacercariae, which can remain infectious for several months. After ingestion, the young larvae penetrate the intestinal wall and migrate to the liver, where they wander for several weeks before settling in the bile ducts. The full cycle takes at least 4 to 6 months. Many horses naturally have some resistance to liver fluke. Although horses can be infected, they are generally able to immobilize and then expel the parasites.
Due to their naturally high resistance, there are often no clear clinical signs. The symptoms are mostly non-specific: weight loss, decreased appetite, a dull coat, anemia, diarrhea, or similar vague complaints. Young horses are more often infected than adult animals. Liver fluke infections are often found in horses that also carry many other gastrointestinal worms, such as bloodworms or roundworms. Therefore, always have a fecal test done if you suspect liver fluke.
Diagnosing liver fluke is not easy. A correct assessment of factors that determine pasture contamination is crucial. Actively monitor moisture levels, temperature, and previous grazing by ruminants. This history, combined with blood tests for liver enzymes, fecal examination, and the horse’s clinical picture, will lead to a probable diagnosis. If a fecal test is performed with a sufficient amount of manure and the correct technique, it can confirm the diagnosis by detecting liver fluke eggs. At Worm&Co, we use the modified Dorsman method. This test is qualitative, which means we can determine with certainty whether the horse is infected or not. Because liver fluke infections are almost always seen in horses with gastrointestinal worms, we always combine the liver fluke test with a standard gastrointestinal worm test using the McMaster method. If you are interested in having a liver fluke fecal test performed on your horse, you can easily order a worm check kit on our website!
In the Netherlands, there are no products registered for the treatment of liver fluke in horses. However, good experiences have been reported with triclabendazole. Due to frequent use of triclabendazole in sheep, many liver flukes have become resistant to this product. If a fecal test shows your horse is infected with liver fluke, we will provide you with a personalized treatment plan. This way, your horse’s health comes first and unnecessary deworming can be avoided. Please feel free to contact our team if you have any questions; we are happy to help!
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