Efficacia della moxidectina nei confronti di popolazioni di cyathostomini resistenti al fenbendazolo Efficacy of moxidectin against fenbendazole-resistant cyathostomins

Cyathostomins are the most important helminth parasites of horses, for their cosmopolitan diffusion, their pathogenic potential and their ability to survive to anthelmintic treatments with major compounds available on the market. Resistance to benzimidazoles is globally diffused, and resistance to tetrahydropyrimidines is increasing as well. Furthermore, in the past few years reduced efficacy of macrocyclic lactones has been reported, especially for ivermectin. Recently, cyathostomin populations with reduced susceptibility to moxidectin have been reported from the Americas and Europe. In Italy, resistance to benzimidazoles has been mostly found in central and northern regions. The present trial, carried out in two horse stables with a known history of benzimidazole-resistant cyathostomins since 2008, aimed at evaluating the efficacy of fenbendazole and moxidectin against local cyathostomins by the Fecal Egg Count Reduction Test. The cyathostomin populations present in the two stables confirmed to be resistant to fenbendazole (efficacy ranging from 43.7 to 56.7%) and showed to be susceptible to moxidectin (100% of efficacy). The present work confirms the presence of fenbendazole -resistant cyathostomin populations in Italy and supports the necessity of effective worm control programs based on scientific criteria to limit the spread of drug resistant cyathostomins.