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Liver Fluke in Sheep

The Crookwell district is liver fluke country. Fasciola hepatica, the liver fluke, is widespread across NSW in areas where annual rainfall is 600mm or higher. In good years, that includes the Tablelands and nearby slopes.

Liver fluke can develop to sexual maturity in sheep, cattle, horses, pigs, goats, alpacas and deer. Fluke don’t just affect production animals - other hosts include kangaroos, wombats and rabbits, and these species can act as reservoirs, maintaining contamination of pastures.

Fluke are dangerous! They are a zoonosis (ie can affect humans) with people becoming infected by eating watercress growing in contaminated creeks.

Apart from the enormous cost of fluke drenches and death of stock in severe infestations, fluke cause generalised loss of production with poor growth rates, reduced milk production, lower lambing percentages etc.

Life cycle

Liver fluke have two key requirements – a suitable snail to act as intermediate host and a watery environment. That means land with slow-running streams, springs, marshes and irrigation channels. The most important snail used by fluke in Australia as intermediate host is Lymnaea tomentosa, a native freshwater snail.

Fluke eggs pass out in faeces onto pastures and hatch in wet areas when temperatures rise above 10 degrees C. The warmer the temperature, the faster the eggs take to develop into larvae (between 3 to 12 weeks). These first larvae invade the snails and go through a number of developmental stages over 2 to 3 months to become a tadpole-like organism (cercariae). These leave the snail and swim to vegetation where they encyst.

These encysted metacercariae are the infective stage of liver fluke. When eaten by sheep, cattle or other hosts (including humans) they “excyst” in the small intestine, releasing small immature flukes. The young fluke pass through the gut wall into the abdominal cavity, penetrate the liver capsule and migrate through liver tissues for 6 to 7 weeks before entering the bile ducts and growing into adult fluke. From 8 to 10 weeks after being eaten as larvae, adult flukes are laying eggs (between 20,000 to 50,000 per day) that pass out in faeces and the cycle starts again.

Grazing patterns and infection

By choice and if other food is available, sheep and goats will graze away from the wet marshy areas favoured by snails with metacercariae encysted on vegetation (cattle prefer the wetter pastures). All species are more likely to ingest the infective fluke when forced to graze in swampy areas during extended dry periods. Stock can also be forced to graze in these areas if a property is overstocked.

Diagnosis

At CVH we can detect fluke eggs in faecal samples and/or undertake autopsies to identify adult fluke in the bile ducts. We also recommend the ELISA blood test. We use this to provide an overall profile of fluke infections on a property – the test shows whether stock have been infected by fluke in the previous 3 months, regardless of whether they have been treated or not.

The ELISA blood test is more sensitive than the fluke egg test in faeces. The process involves taking 10 blood samples per representative group of stock ie those that have been running on fluke-prone country.

Symptoms

At CVH we most commonly see the chronic form of the disease in both sheep and cattle, after the adult fluke have reached the bile ducts. Here they ingest blood and cause inflammation of the ducts. Classic symptoms include severe anaemia with oedema (fluid) under the jaw (“bottle jaw”), pale membranes in the mouth and eyes, poor appetite and weakness.

Acute liver fluke disease (fasciolosis) – more commonly diagnosed in sheep – usually results from a massive but brief intake of metacercariae when stock are forced to graze heavily contaminated wet areas. Some animals may show no obvious symptoms, others will have abdominal pain and/or develop jaundice. Death is usually due to blood loss from haemorrhage in the liver caused by migration of immature fluke.

Livestock with subacute fasciolosis have jaundice, ill thrift and anemia from the extensive damage caused by burrowing fluke. Death usually occurs in 8 to 10 weeks.

Treatment

Talk to our vets about the diagnosis, treatment and control of fluke. Treatment can be complex, depending on the nature of the disease, and it is not a substitute for an effective control program. In acute fluke outbreaks or the management of chronic fluke infestations, note that only some anthelmintics are effective against immature fluke. Success will depend on the correct selection and use of chemicals – talk with us about treatment options.

Strategic control

Managing liver fluke on your property requires a three-pronged approach:

  1. Strategic drenching with the correct chemical groups to reduce the number of fluke in the host and the number of fluke eggs on pasture. In Crookwell, we recommend drenching all livestock species in autumn and spring to achieve maximum effect against both immature and adult fluke, protecting stock and reducing pasture contamination.
  2. Reducing the number of host snails in the environment. This can be challenging as the snail reproduces readily and there is as yet no product registered for snail control in Australia. This means managing the environment as below is critical.
  3. Managing these fluke-prone areas to reduce exposure to infection ie fencing out your poorly drained snail habitats is the most economical and straightforward way to keep stock out of contaminated areas. Or, drain these wet pastures. The use of trough watering systems can be very effective. Fence out fluke areas, and ensure the trough system uses water from non-fluke contaminated sources.