The drug, monepantel – sold under the trade name Zolvix – was reclassified from POM-V to POM-VPS in 2017, despite the BVA’s concern it was “in direct opposition to the trend in Europe”
The first case of resistance to a key anthelmintic drug for sheep has been reported – slightly more than a year after the VMD reclassified it from POM-V to POM-VPS.
At the time the drug, monepantel – sold under the trade name Zolvix – was reclassified in 2017, the BVA registered its concern and warned only vets should prescribe Zolvix to safeguard its efficacy.
In a press release in March 2017, then BVA president Gudrun Ravetz said: “The reclassification of Zolvix from POM-V to POM-VPS is in direct opposition to the trend in Europe, where we are seeing increased control over dispensing of anthelmintics in species where resistance is a serious threat to animal welfare and profitable production.”
The first UK report of monepantel resistance in the UK, ”Lack of efficacy of monepantel against trichostrongyle nematodes in a UK sheep flock”, has been published in Veterinary Parasitology.
The paper revealed monepantel was found to be less than 80% effective and resistance developed despite attempts to use the drug responsibly.
The predominant resistant nematode was Trichostrongylus vitrinus and the authors expressed their concern for the sustainability of pharmaceutical control of ovine roundworms.
Reacting to the news, BVA president John Fishwick said: “This is the first UK report of resistance to the anthelmintic monepantel and it is a very worrying development, underlining the need for these medicines to be responsibly prescribed and used carefully.
“We know resistance to anthelmintics has been increasing in grazing animals, and if it becomes widespread, it could have a potentially catastrophic impact on animal welfare and production as our ability to tackle parasites becomes more limited.”
In a statement, the VMD said: “The publication… detailing the first case of lack of efficacy of monepantel in a sheep flock in the UK highlights the need for adoption of best practice guidance regarding integration of the group 4-AD and 5-SI anthelmintics into worm control programmes.
“[Sustainable Control of Parasites in Sheep] guidance recommends targeted use of these ‘newer’ anthelmintics as a quarantine drench or mid/late-season lamb break dose, alongside appropriate pasture management to reduce the risk of selection for anthelmintic resistance.”