Liver fluke can cause serious production losses, anaemia, bottle jaw and death. Liver fluke is present in all states but the most at-risk stock are those in south-eastern Australia where there is a suitable habitat for the host snails. This includes the tablelands, coastal margins and irrigation areas of NSW and Victoria.

Lifecycle

Liver fluke have two hosts, firstly a snail (Lynnaed species) which is 6 mm long and has a clockwise or right-hand spiral thread (if the snail is lain on the hand with the tip pointing away from the viewer, the opening is on the left). Snails require water to survive, e.g. in marshy or slow running streams. 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 from mid- to late-spring. In severe infestations, 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, drench with triclabendazole in late summer to mid autumn (April/ May) and if necessary in mid winter (August) to eliminate fluke picked up in autumn. In some regions an additional drench may be required in February to stop acute fluke killing sheep. On some properties strategic control is not required but can be based on monitoring. For more information, refer to the NSW DPI Primefact Liver fluke disease in cattle and sheep http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0004/114691/liver-fluke-disease-in-sheep-and-cattle.pdf.

Monitoring
Either test faecal samples to check for fluke eggs or use a blood “liver fluke ELISA” test that can detect 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 check 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.