The initial investigation into suspected reduced ivermectin efficacy was undertaken by the veterinary practitioner in conjunction with APHA. The results from the on-farm study led to a controlled efficacy trial being undertaken at the Moredun Research Institute in collaboration with APHA and AHDB Pork using worms from the farm on which the initial investigation took place. This trial confirmed the finding of the first reported case of resistance to ivermectin in adult O. dentatum worms in the UK.
Factors that might have played a role in ivermectin resistance development include long-term use of ivermectin for parasite control in pigs on the farm and continued use of outdoor paddocks without land rotation for decades. Fortunately, FECR testing suggest that benzimidazole treatment remains effective. Wider testing is recommended to determine whether this detection is an isolated incident or is of wider significance. Faecal egg count reduction (FECR) testing is a well-recognised preliminary test to assess suspected reduced anthelmintic efficacy.
July 2018/ APHA-GB Emerging Threats
Quarterly Report / United Kingdom.