Liver fluke infections have increased in some European countries by 12 fold in recent years.
The underlying cause seems to be climate change, particularly the trend for milder, wetter weather. These climate changes improve the survival and development of liver fluke stages that live outside the sheep and its intermediate host, the mud snail. This may be why liver fluke has spread further across some countries in the past 40 years.
In the 1970s fluke was pretty much restricted to occasional cases in the wetter areas, but has now spread into traditionally dryer regions. The climate changes have also meant that fluke has become less seasonal; more fluke survive over winter on the pasture leading to more infections breaking out earlier in the year.
Treatment strategies are quite dependent on weather conditions, lambing and service dates on each farm. Timing is also based on the assumption that peak levels of infective stages on the pasture will usually occur in autumn and winter. The following strategies are only a guide and advice should be sought from your vet or animal health advisor for your individual farm.
In years with normal or below average rainfall, treat for adult fluke in late April/early May. Later in October, treat for adult and immature fluke and then treat for adult fluke in January.
In years with above average rainfall, or high risk years, treat for adult fluke in late April/early May. Four to six weeks later treat for adult and immature fluke in June. This approach, ie treating for both immature and adult fluke, should be followed up in October with flockowners treating for adult an immature fluke again in November. The cycle is completed with a treatment for adult fluke in January.
Animals should be weighed to prevent under dosing which can leave some fluke alive and help select for resistance. Dosing equipment needs to be regularly checked and calibrated and ensure the drench goes over the back of the tongue or the injection goes into the animal.
With regard to flukicides, Triclabendazole is licensed to kill immature flukes from two days old and adult fluke. Closantel will kill adult fluke and immature fluke down to five-six weeks of age, and delays egg shedding for up to 13 weeks after treatment.
Albendazole and oxyclozanide drenches and a nitroxynil injection are also licensed for adult fluke in sheep. Nitroxynil has some activity against immature fluke.
(Source – Farming Life – 26/09/2013)