Liver Fluke in Sheep and Goats

Introduction

Liver fluke (Fasciola hepatica) is a parasite affecting a range of livestock and other species. Final hosts in which it can develop to sexual maturity include livestock such as sheep, cattle, horses, pigs, goats, alpacas and deer. Other species include kangaroos, wallabies, rabbits, and humans. People can be infected by eating water cress or other plants growing along creeks in fluke-infested country.

Millions of sheep, goats and cattle graze pastures where liver fluke is endemic, mainly in south-eastern Australia.

Adult liver fluke (marked x) on cut surface of liver. Source: Bruce Watt Central Tablelands LLS

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 swimming larvae and provide a habitat for aquatic 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, and to small areas in Queensland and South Australia. Liver fluke may also be found in irrigation areas and also coastal areas of Queensland.

Life cycle

Adult fluke in bile ducts produce eggs that flow in the bile to the intestines and are passed out in the host’s faeces. The eggs hatch in wet areas on pasture when mean daily temperatures are over 10°C. Larvae (miracidia) invade the intermediate hosts, which are aquatic lymnaeid snails: most commonly Austropeplea (Lymnaea) tomentosa in southern Australia and New Zealand.

In coastal subtropical Queensland and NSW, the exotic snail Pseudosuccinea (Lymnaea) columella has become endemic and is known to transmit liver fluke. A third host snail, Radix viridis – has been introduced from the Pacific Islands (Guam). It lives in various habitats and its range is expanding.

Once inside the snail, larvae develop and multiply as sporocysts, rediae and cercariae. A single snail can produce up to 4,000 cercariae. The tadpole-like cercariae leave the snails, swim until they find vegetation and form cysts (metacercariae), which are the stages infective to sheep, goats, cattle, other species and humans. Grazing animals ingest the cysts, which release immature flukes in the small intestine. The young flukes 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. Egg production starts 8–10 weeks after infection. Adult fluke can live for several years and produce over 20,000 eggs per day.

Liver fluke disease (fasciolosis)

Liver fluke disease can be acute, sub-acute or chronic, depending on the size of the infection and how quickly it is acquired. Disease is due to haemorrhage and tissue damage from immature fluke migrating through the liver, from damage to the bile ducts, and blood loss due to the feeding adult fluke.

Acute fasciolosis: Possibly causes death, with or without abdominal pain, jaundice and anaemia.

Sub-acute fasciolosis: Causes jaundice, ill thrift, anaemia, and possibly death after several weeks.

Chronic fasciolosis: The most common form; slowly developing clinical signs include anaemia, loss of appetite, and ‘bottle jaw’ (submandibular oedema).

Black disease: This 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 young fluke migrating through the liver. It is preventable by vaccination with 5-in-1 (clostridial vaccine).

Treatment and prevention

Treatment is by use of flukicide drenches — antiparastic drugs effective against liver fluke. As some drenches only kill adult liver fluke, care should be taken to ensure an appropriate flukicide is chosen according to the season and the risk of immature fluke being present.

Control is by combining strategic treatment with flukicides and grazing management.

As ‘flukey’ areas are confined to certain parts of a farm, grazing of 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. 1–3 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 that has been tested for efficacy) should be used.

Newly-introduced animals should be assessed for risk and given an effective flukicide prior to grazing.

All flukicides are subject to the development of resistance. This has been confirmed in triclabendazole and closantel.

A simple method of checking for resistance is to take dung samples for a fluke egg count on the day of treatment, then again 30 days after treatment. In winter, there should be no eggs in the dung samples

Regular monitoring should be undertaken. Testing options include:

• Liver fluke egg counts, using faecal samples, but remember fluke eggs only appear in the faeces of the host 8–10 weeks after infection. Samples from a large number of animals in a mob (minimum 10–15) should be taken as fluke egg excretion is not consistent.
• An antibody test (ELISA) using blood samples or, in the case of dairy cattle, milk samples.
• A faecal antigen test from: NSW Veterinary Diagnostic Laboratory, Menangle or Charles Sturt University, Wagga Wagga, NSW.

Further control and treatment options

NSW and Queensland

Victoria

Tasmania

South Australia—while liver fluke do occur in South Australia, sheep are no longer run in these areas.

Western Australia—liver fluke does not occur in Western Australia.

Acknowledgement

This information is largely drawn from the Primefact: ‘Liverfluke disease in sheep and cattle’ by Joe Boray.

Further information

NSW DPI Primefact – Liverfluke the Facts (86 KB)

NSW DPI Primefact – Liverfluke disease in sheep and cattle (555 KB)