The little-known scenario of anthelmintic resistance in equine cyathostomes in Italy.

Cyathostomes (Nematoda, Cyathostominae) cause colic, decreased performance and growth, peripheral edema, and dysorexia in equids. Also, the synchronous emergence of cyathostome larvae encysted in the colon and cecal wall causes larval cyathostominosis, which is characterized by protein-depriving enteropathy, chronic diarrhea, edema, weight loss, colitis, and may be fatal. In the past few decades, drug resistance in cyathostomes has become widespread, especially for benzimidazoles. Resistance to tetrahydropyrimidines is still confined to a few areas, and the recent reports of reduced efficacy in macrocyclic lactones are of great concern. Although cyathostomes are widely distributed in Italy, with a prevalence up to 100%, information on the presence of drug-resistant cyathostomes is scarce. The first study investigating drug resistance was conducted on a few farms in 1992 and showed the presence of cyathostome populations resistant to the (pro)benzimidazoles in northern Italy. A second survey was carried out 14 years later, with the focus on farms in central and southern regions. Cyathostomes resistant to fenbendazole and pyrantel pamoate were found, while macrocyclic lactones remained 98-100% effective. Recently, the efficacy of oxibendazole (97%) and moxidectin (100%) in removing fenbendazole-resistant cyathostomes in Italy has also been demonstrated. These few studies indicate that drug-resistant cyathostomes are present in multiple regions of Italy, but geographically and numerically broader investigations of farms are necessary. Finally, there is the undoubted need to use the remaining fully effective drugs (such as moxidectin) in a proper way to preserve their efficacy as much as possible.