20/11/2025
Liver fluke, or fasciolosisโ๏ธ
Liver fluke, or fasciolosis, is a significant parasitic disease in sheep caused primarily by the flatworm Fasciola hepatica. The parasite's life cycle involves a specific type of mud snail (Galba truncatula) as an intermediate host, meaning the disease is prevalent in wet, marshy, or poorly drained pastures where these snails thrive.
Symptoms and Disease Forms
- Acute fasciolosis: Occurs after a massive, short-term intake of metacercariae, usually in late summer to autumn. Immature flukes cause extensive damage and internal bleeding as they migrate through the liver tissue, often resulting in sudden death without obvious prior symptoms.
- Subacute fasciolosis: Results from a smaller, but still significant, intake of metacercariae over a longer period. Signs include rapid weight loss, weakness, severe depression, and anemia, with death possible after several weeks.
- Chronic fasciolosis: The most common form, typically seen in late winter and spring, caused by a prolonged intake of low numbers of metacercariae. Adult flukes in the bile ducts feed on blood, leading to progressive weight loss (ill-thrift), poor fleece quality, anemia (pale gums/eyes), and a characteristic fluid accumulation under the jaw called "bottle jaw" (submandibular edema).
Control and Treatment
An integrated management approach combines strategic treatment with grazing management to break the fluke lifecycle:
- Treatment with flukicides: Different drugs target different life stages of the fluke.
- Triclabendazole is unique as the only active ingredient effective against all stages, including the early immature stage that causes acute disease. Resistance to flukicides, especially triclabendazole, is a growing concern, so veterinary advice should be sought for a targeted treatment plan and to confirm efficacy.
- Pasture management: Minimizing snail habitats by improving drainage or fencing off high-risk, wet, or marshy areas is key.
- Grazing strategies: Avoid grazing sheep on high-risk pastures, especially during peak challenge periods (late summer/autumn).