Liver fluke (Fasciola hepatica) is one of the most economically and welfare-significant parasites of sheep and cattle in the UK and globally. Fluke infestations cause a spectrum of disease from acute hepatitis with sudden death to chronic weight loss and production failure — with significant welfare consequences at every level of severity.
Acute fasciolosis — occurring when large numbers of immature flukes migrate through liver tissue simultaneously — causes hemorrhagic hepatitis, internal bleeding, and sudden death, typically in sheep on high-risk pastures in autumn. Affected sheep may die within hours of first symptoms. Subacute disease causes liver damage, anemia, and weight loss over weeks. Chronic fasciolosis — the most common form — causes progressive weight loss, bottle jaw (submandibular edema), pale mucous membranes, and wool break over months. The chronic form represents prolonged welfare impairment that is often underdiagnosed until animals are severely affected.
Triclabendazole is the only flukicide effective against all life stages including early immature flukes — essential for treating acute disease. Other flukicides (closantel, nitroxynil, oxyclozanide) target different life stages and are appropriate for different disease presentations. FAMACHA scoring for anemia and regular pasture risk assessment guide treatment timing. Resistance to triclabendazole is an emerging problem requiring strategic rotation of flukicide classes.
Liver fluke life cycle requires the mud snail Galba truncatula as intermediate host — snail habitat reduction through drainage and fencing of wet areas reduces transmission risk. Strategic prophylactic treatment in high-risk autumns prevents acute disease outbreaks.
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