Liver fluke are found in most of Victoria and Tasmania, South-Eastern New South Wales, the irrigation areas of NSW and Victoria, the Northern Tablelands and North coast of NSW, and Southern Queensland.

Liver fluke is not found in Western Australia. In Australia, there is only one species of liver fluke found in sheep, Fasciola hepatica.

Liver flukes are fleshy, flat worms about two cm. long. Adult liver flukes live in the bile ducts and juvenile flukes in the liver tissue. Liver fluke mainly infect cattle and sheep but can develop in many animals including: horses, pigs, goats, kangaroos, wombats and rabbits.

Humans can also be infected with liver fluke. Humans are usually infected when they eat watercress collected from contaminated streams, or use contaminated water on fruit and vegetable gardens.

Liver fluke can cause serious economic losses in animals. In sheep, infection with liver fluke reduces production, including wool growth and wool quality, lambing percentages and growth rate of lambs. Sheep can also die as a result of liver fluke infection.

Find out more about liver fluke:

• Life cycle
• Location in the sheep
• Effects on the sheep
• Diagnosing liver fluke
• Treatment

 Liver fluke life cycle

Liver fluke have an indirect life cycle using snails as the intermediate host. The presence of the snail is essential for transmission of the fluke. Without the snails, the fluke cannot become infective to the sheep or other hosts. This explains why fluke infections occur only in the areas where the snails survive. Western Australia has the snails but no fluke.

The hermaphroditic adults lay eggs in the bile ducts of the sheep’s liver and they are eventually excreted in the dung. A fluke can lay 20,000 – 50,000 eggs per day. These eggs hatch and the larvae (called miracidia) infect the snail.

Each larva is capable of multiplying inside the snail to many hundreds of the next larval stage (called metacercariae). These emerge from the snail, attach to vegetation and form a cyst.

The cyst is able to survive very harsh environmental conditions. The transition from egg to cyst takes between five and seven weeks when conditions are favourable, and may be much longer if conditions are not so favourable. When the sheep or other host eats the cyst, it loses its tough wall in the small intestine and the immature fluke emerges.

The immature fluke migrates through various tissues for four to six days until they reach the liver. In the liver they wander through the liver tissue for five to six weeks, eventually settling in the bile ducts. The immature fluke is only about 2mm in length, but can cause enormous damage to the liver tissue.

The full life cycle takes from seven weeks in summer and up to 25 weeks in winter.

The adult fluke can live for 10 years. If things go right for a fluke it can produce over 10,000,000,000 infective cysts.

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 Location of liver fluke in the sheep

Adult liver fluke are found in the bile ducts of the liver.

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 Effects of liver fluke on the sheep

After sheep eat the fluke cyst on grass, a juvenile fluke is released into the sheep's gut and starts its journey to the liver.

The fluke then moves through the liver for six to seven weeks, eating liver tissue and blood. They grow to adults and enter the bile ducts where they feed on blood.

The flukes' eating behaviour causes serious damage to the liver and anaemia due to blood loss. The liver damage and anaemia lead to loss of body weight, reduced wool growth, and reduced milk production and poor breeding performance in ewes. The degree of damage and economic loss varies - the more flukes in the liver the more serious the disease. A well-fed sheep can cope with about 20 flukes.

Acute fluke disease (fasciolosis) occurs soon after sheep are moved to heavily cyst contaminated, wet areas during drought where they eat several hundred fluke cysts in a short space of time. Many flukes develop at once and the result is fatal within a few weeks.

Prior to death sheep may have jaundice or abdominal pain, or be reluctant to move. Chronic fluke disease occurs after a slow accumulation of flukes and is caused by adult liver flukes in the bile ducts. Animals become progressively more anaemic, listless and weak, lose their appetite, lose condition and are reluctant to move.

Some animals develop 'bottle jaw' - a swelling under the lower jaw associated with severe anaemia. These signs may lead producers to misdiagnose the fluke infestation as a barbers pole infestation.

Black disease is a fatal, liver disease of cattle and sheep set off by fluke infection. Sheep can be vaccinated against black disease using clostridial (5-in-1) vaccine. The livers damaged by flukes have no value.

Liver fluke damage to liver

This image was kindly supplied by Dr R Woodgate, Western Australian Department of Agriculture

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 Diagnosing liver fluke

Liver fluke can be diagnosed two ways:

1. Conducting a fluke egg count. This is done differently to a normal worm egg count. It provides a 'present or absent' diagnosis. Because of the potential of fluke to rapidly increase and the damage they cause, if fluke are present the sheep should be treated.
2. Conducting an 'elisa' test on blood or milk. This test indicates presence or absence of fluke in a flock.

Both methods have limitations.

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 Treatment of liver fluke

Treatment options:

• Narrow spectrum, short acting specific for fluke – triclabendazole
• Narrow spectrum (fluke and barbers pole) short acting – nitroxynil
• Narrow spectrum (fluke and barbers pole) long acting on barbers pole – closantel
• Broad spectrum, short acting – oxyclozanide

Resistance to triclabendazole has been found in fluke in some very localised districts in NSW and Victoria.