Update on liver fluke in sheep and cattle

It is difficult to define the true cost of liver fluke infection to UK farming, but the Agriculture and Horticulture Development Board (AHDB) estimated a cost of £6 per infected lamb and £96 per infected beef calf (AHDB, 2012). At the herd level, Fasciola hepatica infection results in an estimated 12% and 6% reduction in net profit on an average dairy and beef unit, respectively (Shrestha et al, 2020). Changing weather patterns in the UK over recent years have often resulted in milder winters and summers that may be hot or wet but are above all unpredictable, affecting the epidemiology of liver fluke (Howell et al, 2023).

The liver fluke life cycle takes around 20 weeks to complete and requires a snail intermediate host (Figure 1). Mature flukes (Figure 2) reside in the liver of the definitive host. Fluke eggs are passed out in the faeces of infected livestock and develop on pasture. This development is temperature-dependent and takes 2–4 weeks. Eggs then hatch to release miracidia that seek out a host snail. After burrowing into the snail via its foot, the parasites undergo clonal division in the snail body cavity over several weeks, producing several thousand genetically identical cercariae that are then released from the snail (Hodgkinson et al, 2018). The cercariae encyst on plant matter as metacercariae, which are the infective stage. When eaten by a grazing animal, the metacercariae excyst and the young flukes migrate through the gut wall into the liver. It then takes a further 10 weeks for fluke to mature and produce eggs that can be detected in faeces.