As with all parasites, the key to controlling liver fluke is ‘know thy enemy’.
There have been a number of reports of liver fluke across the district in recent months. Producers have become aware of high burdens of this parasite due to illness and death in stock as well as reports from the abattoir and results from WormTests.
Adult liver fluke (adult fluke) can live in the liver of a number of host species, including sheep, cattle, horses, goats, and alpacas. Adult fluke lay eggs that pass through the bile duct, travel through the intestinal tract, and end up in the feces.
Under optimal conditions, the eggs hatch in wet areas. The first larval stage invades the intermediate host, the lymnaeid snail, where they develop and multiply. The final larval stage leaves the snail and swims until it encysts on vegetation, where it can infect grazing livestock. This stage can survive for many weeks at temperatures below 20°C but it will be destroyed in a short time at higher temperatures.
If ingested, immature fluke are released in the small intestine before entering the abdominal cavity and migrating through the liver tissue. Their final destination is the liver bile ducts where they become adult fluke and the life cycle begins again.
The time between ingestion and commencement of egg laying in the bile ducts is around 8-10 weeks. Eggs hatch when mean temperatures increase above 10°C, and eggs develop into the first larval stage between 21 days (in summer) and 90 days (spring/autumn).
Three things are required for liver fluke infection at the property level:
- a suitable snail species
- a suitable environment for fluke eggs, snails, and larval fluke - namely springs, slow-moving streams with marshy banks, irrigation channels, and seepages
- adult fluke in a host species that has access to the suitable environment containing the snail species.
So why issues with liver fluke in the Palerang district during a dry spring?
My theory is that during the warm wet summer and autumn last year, snail numbers increased dramatically due to an increase in suitable habitat, and therefore so did fluke numbers.
If the most important fluke drench that is effective against all stages (the April/May drench) was missed, adult fluke numbers could accumulate in livestock. A perfect storm may have been created in the dry spring due to nutritional stress and grazing in previously marshy areas (where green pick may be heavily contaminated).
Disease due to liver fluke can present in a number of ways. Most commonly, liver fluke infection is quite chronic. The adult liver fluke in the bile ducts consume blood, causing anemia and chronic liver inflammation. Clinical signs develop slowly, with animals becoming increasingly anemic, pale, and reluctant to travel. Some may have decreased appetite and develop ‘bottle jaw’, or fluid under the jaw.
In acute infection animals may show signs of abdominal pain and become jaundiced prior to death from blood loss. Death usually occurs in 8-10 weeks due to severe anemia and liver failure. If infection is less acute, animals may present with jaundice, poor body condition, or pale mucous membranes.
If there is a history of liver fluke on your property you probably should be. In sheep, consider a WormTest (and tick the box for liver fluke testing). In cattle, you may be better off looking for antibody to liver fluke in blood samples as looking for liver fluke eggs is generally considered less reliable. If you have liver fluke on your property, consider drenching all stock with a drench that is effective against all stages of fluke and a regular control program.
Be sure to discuss your options with your local veterinarian.
And remember that liver fluke control is more than just about reliance on drenching – consider improved drainage, fencing, and grazing management.