Shaping the future of animal health
South Africa

LIVER FLUKE IN CATTLE AND SHEEP

The parasite, its impact on the animal, and its control

Corné Mostert

Fascioliasis, caused by the liver fluke, is one of the most prevalent parasitic diseases in the world, including South Africa. It is responsible for major economic losses due to livers that are rejected at abattoirs, reduced milk and meat production (growth) and reproduction, secondary bacterial infection, and even death.

The parasite

Two liver-fluke species are found in South Africa, the common liver fluke (Fasciola hepatica) and the giant liver fluke (Fasciola gigantica). The lifecycle of the liver fluke is complex, with various stages of development inside and outside the livestock. Liver-fluke populations are maintained through the presence of freshwater snails that serve as intermediate hosts. Wet and marshy areas such as swamps, streams, and earthen dams are ideal habitats for the survival of freshwater snails. The water must be slow-moving or still.

The eggs are excreted along with the animal’s faeces and rainfall flushes them out of the excrement and maintains the bodies of water where freshwater snails can survive. Temperature also plays an important role. Both the liver fluke and freshwater snail thrives during the warmer months of the year. When the average daily temperature starts to drop below 10 °C, the eggs stop hatching, the development of liver-fluke larvae inside the freshwater snails slows down, and the snails become inactive. In the colder areas, the lifecycle of the liver fluke will therefore come to a halt. However, in warmer areas, the lifecycle can continue throughout the year, as do fluke infections, and the flukes’ numbers will increase.

Effect on the animal

 

The liver fluke causes severe damage to the animal from the time the metacercaria (infectious stage) is ingested until it is brought under control (or until the mature liver fluke dies – which can take 2 years). In cattle, ±25% of the metacercaria reach the liver within 2 weeks to 85 days from time of consumption. The rest migrates through the body and inflicts damage to other organs until the flukes eventually die.

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The liver is one of the most important organs and is involved in more than 500 functions in the animal’s body. It can be regarded as both the animal’s “pantry” and “oven”. If the liver is not fully functional due to damage caused by the liver fluke, the following functions, amongst others, are impaired:

 

  • Protein and energy metabolism – affects growth and production.
  • The liver’s ability to produce bile salts (the precursors of cholesterol and sex hormones, as well as being required for efficient digestion in the lower intestinal tract and the production of Vit A from carotene) – affects reproduction and growth.
  • The ability to store trace minerals – affects reproduction and immunity.

Control strategy

Effective liver-fluke control can be a challenge. Control must be aimed at reducing the number of parasites in the host and to limit the fluke population in the area. Effective and sustainable control is dependent on an integrated parasite-control programme that includes, amongst other measures, chemical control within the animal, pasturage management, fencing off contaminated areas (where possible), and the repair of leaking troughs (which reduces the habitat of the intermediate host). The chemical control of freshwater snails through the administering of copper sulphate is usually impractical and may be harmful to the animals.

The timing of fascioliasis is one of the two key factors of effective liver-fluke control. It is based on the following:

  • Curative treatment:

Autumn (April/May) – with the autumn treatment, it is essential to control early immature, immature, and mature flukes to reduce liver damage.

  • Preventative treatment:

Late winter / early spring (Aug./Sept.) – the treatment is essential to remove the remaining flukes and reduce recontamination of the pasturage.

  • Optional treatment:

Summer (Jan./Feb.) – in areas where liver-fluke contamination is high, this treatment is necessary to ensure optimal control.

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Product choice is the second key factor in effective control of the liver fluke. Use Flukazole C once to twice in the liver-fluke control programme, especially in areas where contamination is high.

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