Vets from Scotland’s Rural College have warned sheep farmers liver fluke epidemics have not disappeared and should not be forgotten.
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 experts have warned there is no cause for flock masters 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.
She said: “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 fewer infectious cysts on the autumn grass for sheep to ingest. In addition, increased awareness of fluke encouraged farmers to treat their stock for fluke and reduced losses.”
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 to 12 weeks to develop into adults in the bile duct. Heavy infections can lead to sheep deaths after 4 to 8 weeks, due to haemorrhage and destruction of the liver. Ingestion of smaller numbers means fewer deaths, but sheep are unhealthy and fail to thrive.
Ms Stevenson warns the bad memories may have faded, but another wet summer could mean 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 added. “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 to break the fluke cycle.”
Treatment should be targeted at killing adult fluke so products aimed at juvenile flukes, such as those containing triclabendazole, are not recommended at this time of year.