- Liver fluke (Fasciola hepatica) are large, flat, leaf shaped parasites found in the liver.
- Adults are approximately 2cm long and 1cm wide while immature fluke are millimetres long.
- Liver fluke require specific freshwater snail species to complete their life cycle; hence the problem occurs where there is open water, which allows the survival of snails, and the presence of the intermediary snail species.
- Liver fluke can infect other hosts (such as macropods and wildlife) and so persist readily in favourable environments.
- Disease can be acute (following rapid uptake of large numbers of larvae) or chronic (where a significant adult burden exists in the liver) or secondary to infections in damaged livers (e.g. black disease due to Clostridium novyi).
- Liver fluke is estimated to cost the Australian sheep industry approximately $40 million per annum.
- Liver fluke disease (fasciolosis) is classed as acute or chronic.
- Acute fasciolosis often does not show obvious clinical signs, affected sheep simply dying suddenly without any sign of struggle.
- Affected animals may go down and die within minutes if driven at pace. On close examination anaemia and abdominal pain may be detected.
- Chronic fasciolosis is more common and reflects the long-term loss of liver function. Sheep generally display ill thrift, anaemia and bottle jaw.
- Where liver fluke is present, deaths from Black disease may occur if sheep have not been vaccinated.
- Intermediate stages released from snails form cysts on pasture which are then ingested by grazing livestock.
- The ingested immature stage fluke migrate from the small intestines through internal organs to finally settle into the liver and reach maturity in the bile ducts.
- Where mature fluke is present, testing for eggs in the faeces is a reliable method of confirmation; however, egg numbers often do not correlate to the liver damage being caused, nor to the size of the fluke burden.
- Based on flock history, environment and post mortem findings.
- Triclabendazole is the only drench which can be used to kill all stages of the Liver fluke within the sheep. Others will kill the mature parasite (in the bile ducts) but will have varying degrees of effectiveness on migrating stages.
- There is increasing resistance to Triclabendazole and other parasiticides. This can make the control of liver fluke on affected properties challenging.
- Good biosecurity practices should be used when introducing new stock on farm.
- Effective, strategically timed oral drenching of sheep is very important. This controls liver fluke egg production and subsequent pasture contamination by limiting infected animals shedding of eggs in their faeces.
- Drenching stock when they exit a paddock with marshy ground, which supports a snail population, will both reduce the parasite burden on the sheep as well as preventing them from shedding eggs in subsequent paddocks.
- Avoid exposing animals to marshy areas infested with snails, especially in dry periods when water levels in the marshy areas are lower and animals have easier access to contaminated herbage (around the water source). Graze such paddocks with adult sheep and cattle as they have a greater tolerance to the parasite and preferably when water levels are high.
- Clean water troughs regularly to prevent the establishment of snail colonies. Where possible, fence off marshy areas and stream banks which offer a suitable habitat for snail survival.
- Monitoring fluke burden and fluke resistance to chemicals, combined with strategic drenching and livestock management is essential for control within endemic regions.