Liver fluke can cause serious production losses, anaemia, bottle jaw and death.
Lifecycle
Liver fluke have two hosts, firstly the snail which is 6 mm long and has a clockwise or right-hand spiral thread. From the snail, young fluke encyst on pasture that is then grazed by sheep. The young fluke burrow through the gut and migrate to the liver, finally settling in the bile ducts where they feed on blood.
Young fluke typically are present on pasture in mid- to late-spring. In severe infestations, such as irrigation, sheep can die of acute fluke by mid-December due to massive numbers of young fluke migrating through the liver. More commonly, adult fluke develop by February. Depending on the season and environment, fluke pickup will continue until early winter. In some mild regions fluke will continue to be picked up throughout the year. Fluke snails hibernate in winter when a large proportion of infected snails will die.
Many animals including wildlife, can carry fluke, so it is difficult to eradicate unless stock are excluded from all waterlogged and swampy areas.
Principles of control
Strategic drenching
The frequency of drenching will vary between regions and farms depending on the local lifecycle and climate. Typically, a drench may be required from late summer to mid autumn and a second drench in mid winter to eliminate fluke picked up in autumn. In some regions an additional drench may be required in December to stop acute fluke killing sheep. On some properties strategic control is not required but can be based on monitoring.
Monitoring
Either fluke test on faecal samples to check for eggs or use a blood “liver fluke ELISA” test that can test infestations as young as 2 weeks. These tests provide the basis for drenching. With sporadic infestations fluke monitoring should take place in late summer/early autumn and mid winter.
- Do you know the fluke status of sheep on your property
If you are uncertain of the fluke status on your property, monitor mobs of sheep grazing waterlogged or swampy paddocks. Alternatively, organise feedback from sheep sold to an abattoir to assess for evidence of fluke in livers.
New sheep
If sheep come from a fluke infected area, drench them on arrival with Triclabendazole or, if uncertain, do some fluke tests to decide if treatment is necessary.
Control snails
On some farms you can control fluke by fencing off swampy areas. This will stop the lifecycle if all ‘fluke prone’ areas are isolated.
Drench groups
Triclabendazole is the most effective drench that kills all larval stages. Other products do not kill young larval stages but are still effective against adults. There is evidence of resistance to flukicides, so rotation of effective drenches is desirable rather than relying on Triclabendazole. Consult your veterinarian for advice on regional control programs.
