11th October 2021
A dry, cool spring across most of the UK, followed by some hot, dry spells over the summer, means the liver fluke risk is generally going to be low this autumn and winter. However, the Sustainable Control of Parasites in Sheep (SCOPS) and Control of Cattle Parasites Sustainably (COWS) groups say producers need to test on their own farms to avoid treating unnecessarily or being caught out – and need to consider treatment options carefully given the withdrawal of Trodax from the market.
Speaking on behalf of both groups, Philip Skuce of the Moredun Research Institute says: “We are already beginning to see the first signs of liver fluke infection acquired this year. Using lambs and calves born this spring as sentinels for fluke infection in the West of Scotland, we have seen a significant proportion of both serum antibody and coproantigen tests come back positive. This suggests some animals encountered a fluke challenge as early as mid-July. This may seem odd in such a dry year, but many farms rely on field springs and streams to provide water for grazing stock, which can lead to permanent wet patches where the mud snails can persist. This is supported by negative test results for a group supplied by a water trough.”
Matt Colston, a vet with Elanco Animal Health, adds: “In a year like this, it is imperative we use the tests available to monitor the fluke situation on individual farms. We can’t just make assumptions based on general forecasts or previous history. Each farm needs to know if treatment is required, when to do it and what product to use.”
The NADIS Liver Fluke Forecast, based on the latest Met Office rainfall and temperature data, also suggests a generally low risk this autumn. However, there are indications of a moderate risk in some parts of the west of the UK, including Western Scotland and Northern Ireland, and the possibility of a higher risk where animals are forced to graze areas where snails are present. Avoiding areas such as open watering points is one way to reduce the risk to stock, with SCOPS and COWS recommending farmers access useful information from Moredun to Fight the Fluke and Test Don't Guess.
The liver fluke treatment situation has been further complicated by the discontinuation of the flukicide Trodax. The injectable anthelmintic (nitroxynil), manufactured by Boehringer-Ingelheim, was licensed for use in sheep and cattle in the UK with activity against liver fluke from immature through to adult stages. It was valuable because of its spectrum of activity and because it was also a different chemical class to the other flukicides (triclabendazole, closantel etc) so allowed for a strategic rotation of products.
The withdrawal of Trodax from the market means there are now only four actives authorised in the UK and available for sheep – and two of those are adulticides that only kill adult fluke. There are five actives in cattle, three of which are adulticides.
Rebecca Mearns, Sheep Veterinary Society President, says: “To minimise the extra pressure on the only two actives that can kill immature fluke (triclabendazole and closantel), we need to be more careful than ever to make informed decisions about timing of treatment and product choice. We cannot afford to guess. There are good diagnostic tests available and we urge livestock farmers to consult their vet or adviser to decide how best to investigate whether fluke is present and what actions, if any, to take.”
There are other flukicides with nitroxynil as the active ingredient available outside the UK and it may be possible for veterinary surgeons to import these under a Special Import Certificate (SIC) obtained from the VMD in accordance with their clinical assessment – see the relevant section on the VMD website.