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Liver fluke (sheep)

Liver fluke, Fasciola hepatica, is a highly pathogenic parasite that causes severe liver damage, especially in sheep, and can result in the sudden death of previously healthy animals, costing the industry millions of pounds a year.

Now spreading to new regions liver fluke can increasingly be found throughout the UK, largely due to the impact of climate change, including:

  • Warmer temperatures throughout the year
  • Increased rainfall in autumn and winter
  • Dry eastern areas becoming wetter
  • Flooding moving snails infected by the parasite into new areas
  • Increased movement of liver fluke infected animals around the country
  • Resistance to some commonly used flukicides

Indeed, the changing weather patterns over the last decade has affected the lifecycle, allowing both the level and timings of fluke challenge to become more variable.

Liver fluke lifecycle

The liver fluke lifecycle is comprised of two main phases (1) inside the animal, and (2) outside the animal. Both phases are important and influence the treatment and management required. For both cattle and sheep the lifecycle is largely the same with the only difference being the length of time it takes in the animal (the lifecycle inside the animal from ingestion to egg laying is 2 weeks longer in cattle than sheep).

Liver fluke

Liver fluke develop through 3 stages – early immature, immature and adult – which takes approximately 10-12 weeks. All stages damage the liver and can cause clinical disease and production losses. Once the bile duct is reached, up to 50,000 eggs can be laid by adult fluke every day.

Eggs, passed in faeces, start to develop when temperatures reach 10°C, with most of the eggs deposited over the winter hatching in May and June.

The larvae (miracidium) once hatched seek out mud snails (the intermediate host) to continue their development. Those that are successful then take between 5 weeks and a few months to multiply in number by several hundred times before final stage larvae (cercaria) are released from the snail.

The cercaria form infective cysts (metacercariae) on grass which are consumed by animals such as sheep and cattle. For long-term sustainable liver fluke control it is important to consider the importance of treating the right stages of liver fluke, at the right time, with the right product as well as adopting the 4 point plan.

The 4-point plan

Developed in conjunction with experts, the 4 elements of sustainable liver fluke control are (see numbers points on the lifecycle):
(1) Pasture protection – to prevent liver fluke eggs reaching the pasture when snails are active.
(2) Pasture management – to reduce snail habitats and therefore reduce snail numbers.
(3) Grazing management – to avoid grazing high risk pastures with susceptible animals at high risk times of year.
(4) Strategic treatments for at risk animals – using the right product at the right time in the right animals.