Sheep farmers are being warned that while liver fluke epidemics may have failed to hit the headlines during the recent winter, they have not disappeared, according to vets from Scotland's Rural College.
The disaster of the wet summer and winter of 2012/13 and the devastation the parasites caused for sheep health in both traditional fluke areas and others previously untouched may not have been repeated this year, but there is no cause for flockmasters to lower their guard.
According to Dumfries-based Vet Heather Stevenson from the SAC Consulting arm of SRUC there are two reasons why liver fluke was less reported: “The very welcome drier summer of 2013 put the brakes on fluke development.
"There were fewer wet areas for the mud snail that hosts the fluke during part of its life cycle and this in turn meant there were fewer numbers of infectious cysts on the autumn grass for sheep to ingest. In addition the increased awareness of fluke encouraged farmers to treat their stock for fluke and reduced losses.”
Liver fluke (Fasciola hepatica) is a parasite of sheep and cattle, but can also infect other mammals including horses, deer, goats, camels and llamas. Adult fluke in the liver produce large numbers of eggs
which are excreted in faeces.
The hatching fluke then penetrate a mud snail (Galba truncatula) where they develop and multiply for several weeks. On leaving the snail they form the infectious cysts which are found stuck to vegetation in greatest numbers during autumn.
Wet summers suit the mud snail host and lead to higher numbers of infectious cysts on the autumn grass. After ingestion the fluke migrate through the liver, taking 10 -12 weeks to develop into adults in the bile ducts.
Heavy infections can lead to sheep deaths after 4-8 weeks, due to haemorrhage and destruction of the liver. Ingestion of smaller numbers means fewer deaths but sheep that are unhealthy and fail to thrive.
Heather warns that the bad memories may have faded but if we get another wet summer we could find ourselves in another battle.
“If it rains a lot this summer fluke eggs
passed in dung at this time of year will end up as infectious cysts on the autumn grazing,” she says. “Since the weather can’t be accurately predicted it is better to be safe than sorry and the May/June period is a good time to treat sheep in order to break the fluke cycle.”
It is recommended that dung samples are collected and checked for fluke eggs
to find out if treatment is required.
Treatment should be targeted at killing adult fluke so products aimed at juvenile flukes, like those containing triclabendazole, are not recommended at this time of year.
The exception to this rule is when testing is being carried out to find out if triclabendazole is working properly on your farm.
This is valuable information to have as it will guide product choice in the autumn.