Liver fluke can be fatal. Charlotte Mouland outlines the key facts about this canny parasite, what disease it causes in ruminants and how best to control it
Liver fluke, by Charlotte Mouland
LIVER FLUKE used to be thought of as a disease only affecting particularly wet farms, but with warmer, wetter weather patterns and increased movement of livestock around the country it is now widespread.
Mature liver fluke parasites reside in the bile ducts of cattle and sheep and release their eggs into the bile, which are eventually excreted in the host animal’s faeces. Adult liver fluke can grow up to 3.5cm in length and take a very distinctive flat, leaf shape. The liver fluke eggs are infective to other ruminants, but only after a number of key steps in their lifecycle. Knowing this helps to explain the seasonality and geographical spread of liver fluke. At temperatures above 10°C, liver fluke eggs develop and hatch into a motile larval stage called a miracidia; Miracidia have a very short lifespan of just three hours and their sole intention in this time is to find a host water snail. If successful, within the snail a further three larval stages develop to form a cercaria; Cercaria are shed from the snail and attach to grass blades, developing into the final and infective larval stage, the metacercariae; Infective larvae are eaten by ruminants and migrate through the liver, causing extensive damage on their way to the bile duct. The liver fluke lifecycle is therefore a very long and detailed process and depends both on the correct temperatures and the availability of water snails.
What disease does liver fluke cause?
There are two stages in the lifecycle where liver fluke causes disease to the infected animal. Firstly, when the larvae migrate through the liver of the sheep or cow which can cause severe tissue damage; the extent of this injury depends on how many larvae are eaten.
The second stage of disease occurs when the mature fluke take residence in the bile ducts. Because sheep have much smaller livers than cattle, the damage caused by immature fluke tracking across the liver is more prominent in sheep and may cause sudden death. Longer-term disease caused by adult fluke damaging the bile ducts is more commonly seen in cattle and can cause weight loss, diarrhoea and occasionally ‘bottle jaw’ (fluid swelling under the jaw).
Control on your holding
There are two ways to control fluke on your farm: a) reducing the water snail populations on the land or b) using flukicides to treat infected animals. Reducing water snail populations isn’t as simple as it sounds, but fencing off wet areas or waterways can help.
Strategic use of flukicides should be considered in holdings that host liver fluke parasites. Unlike with gut worms, adult ruminants don’t develop an immunity to liver fluke, so all ages are susceptible to disease. Work with your vet to determine if liver fluke are present on your holding and devise a specific liver fluke control plan. The long dry weather this summer will probably have pushed stock closer to natural waterways to graze, so we will have to wait and see how this affects the liver fluke picture this autumn and winter.
A liver showing acute damage from liver fluke