Liver Fluke in Cattle

Liver fluke (Fasciola hepatica) is a parasite affecting a range of livestock, and often goes undiagnosed because infected animals show no obvious signs or symptoms while having a hidden impact on production.

Figure 1. Young adult liver fluke (marked x) on cut surface of liver. Image courtesy of Bruce Watt Central Tablelands LLS

Figure 2. Adult liver fluke showing mouth at top with ventral attachment sucker below (damage to specimen visible at lower left). Image courtesy of Mukund Madhav

Figure 3. Pickled liver flukes. Image courtesy of Mukund Madhav

Distribution of liver fluke

Liver fluke occurs in regions and areas on individual farms where watery environments, such as springs, slow-moving streams with marshy banks, irrigation channels and seepages, suit hatching of fluke eggs into free-swimming larvae, and most importantly, also provide suitable habitat for freshwater ‘fluke’ snails.

Liver fluke is limited to the higher rainfall (>600 mm per year) areas of NSW (typically the tablelands in the eastern part of the state, and nearby coastal areas to the east and slopes to the west), Victoria and Tasmania, to small areas of coastal and subcoastal south east Queensland, and small areas of South Australia.

It does not occur in Western Australia (quarantine requirements are in place to prevent its introduction).

Location in cattle

Adult liver flukes are located in the bile ducts of the liver of cattle, and sometimes in the gall bladder. Immature (pre-adult) flukes are found tunnelling (migrating) through the liver.

Life cycle

These trematodes have a two-host indirect life cycle with adult flukes in cattle, and the intermediate stages in freshwater lymnaeid ‘fluke’ snails.

Adult fluke in bile ducts produce eggs that move with the bile into the intestines and then the dung. Eggs released onto wet areas, once free of dung, hatch when mean daily temperatures are over 10°C. The released free-swimming miracidium has 24-30 hours to locate the freshwater fluke snail otherwise it dies.

Once inside the snail, the miracidium transforms and multiplies through several more stages. After 4-7 weeks, tadpole-like cercariae leave the snail, swim around, and drop their tails as they encyst on vegetation to produce the metacercarial cysts infective to sheep, goats, cattle, other species. Infection of a snail with one miracidium can produce over 600 metacercariae.

Grazing animals ingest the cysts with the vegetation. Immature flukes once released in the small intestine penetrate the intestinal wall, make their way to the liver, and then migrate through the liver tissue for 6–7 weeks before entering the bile ducts to become adults. Adult fluke can live for several years and produce over 20,000 eggs per day. The pre-patent period is 8–10 weeks after infection.

The ‘fluke’ snail most commonly found to transmit liver fluke in Australia is the indigenous Austropeplea (Lymnaea) tomentosa (Figure 4), which has characteristic broad triangular shaped, ear-like tentacles. Introduced snails Pseudosuccinea columella, and Radix viridis are commonly found in warmer coastal areas and have been identified as potential fluke hosts.

Figure 4. The liver fluke intermediate snail host, A. tomentosa, has a shell that spirals clockwise and flat, triangular shaped tentacles. Image courtesy of Mark Blacket

Liver fluke disease

Infections have been associated with three types of liver disease in domestic animals:

• Acute (not often seen in cattle).
• Subacute necrotic (death of tissues) disease due to traumatic injury caused by juvenile flukes migrating through the liver.
• Chronic fibrotic (thickening and scarring of connective tissue) disease due to the feeding activities of adult flukes feeding in the bile ducts. The severity of the disease also depends on the size of the infection and how quickly it is acquired.

Sub-acute disease causes jaundice, ill thrift, anaemia, and possibly death after several weeks. Trauma to the liver by the migrating immature fluke predisposes to black disease infection (a bacteria that produces toxins in the liver).

Chronic disease is the most common form of the disease in cattle and is the result of ingestion of metacercariae, usually in small numbers over many months. It is associated with adult fluke in the bile duct. Typically, there is a gradual loss of condition with progressive signs such as weakness, anaemia and lethargy, loss of appetite, and occasionally ‘bottle jaw’ (submandibular oedema) becoming apparent. Cattle develop distended and thickened bile ducts which later calcify to produce what looks like a branching system of clay pipes and referred to as ‘pipe stem livers’ which are thought to indicate protection against reinfection. Some flukes can become encapsulated in the liver tissues and develop cysts, 2-3 cm in diameter. Small adult flukes are not infrequently found in the lungs in semi-caseous nodular lesions.

In beef cattle, clinical signs are seen in yearlings when sufficient numbers of adult fluke have established, or when infections of immature fluke continue in the presence of a substantial burden of adult fluke in the bile ducts.

In dairy cattle, the most common symptom is a loss of body condition after calving and a significant fall in milk production. Affected cattle have rough coats which become pale in breeds, such as Herefords, that have red coats.

Black disease is an acute and fatal liver disease of ruminants such as sheep, goats and cattle, which is caused by the bacterium Clostridium novyi, usually in association with traumatic injury caused by young fluke migrating through the liver. It is preventable by vaccination with a multi-valent clostridial vaccine (e.g. ‘5 in 1’).

Treatment and prevention

Flukicide drenches i.e. anthelmintics effective against liver fluke, are used to treat infection.

Control is by a combination of strategic flukicide treatment and pasture management. As ‘flukey’ areas are confined to certain parts of a farm, grazing these areas can be managed or even precluded. For example, grazing affected areas by the most vulnerable stock (sheep, goats and young cattle) can be minimised.

Strategic treatments can help to reduce liver fluke populations. One to three treatments may be needed per year, depending on the severity of the problem. The most important treatment is the April–May treatment, and a highly effective flukicide (one based on triclabendazole or clorsulon) should be used.

The Annual Program provides liver fluke treatment advice for different regions around Australia.

Regular monitoring should be undertaken. Testing options include:

• A sedimentation / centrifugation test on dung samples for liver fluke eggs, but remember fluke eggs only appear in the dung of the cattle 8-10 weeks after infection.
• An antibody test (ELISA) using blood samples or, in the case of dairy cattle, milk samples.
• A faecal antigen test.

Further information

• NSW DPI primefact: Liver fluke – a review.

Tropical liver fluke

Figure 5. Tropical liver fluke, Fasciola gigantica, adult. Image courtesy of Constantin Constantinoiu