Species-specific identification of equine cyathostomes resistant to fenbendazole and susceptible to oxibendazole and moxidectin by macroarray probing.

This research investigated the resistance of cyathostome horse worm populations in central Italy to fenbendazole, a common deworming treatment, through the Faecal Egg Count Reduction Test. The researchers also tested the efficacy of oxibendazole and moxidectin as alternatives, using a Reverse Line Blot (RLB) assay to identify specific species. They found 97% and 100% treatment effectiveness in oxibendazole and moxidectin respectively and confirmed fenbendazole resistance, while the RLB provided valuable information about the distribution of parasite species under field conditions.

Methods and Objectives

• The researchers wanted to assess the resistance of cyathostome species (also known as small strongyles – a type of parasitic roundworm in horses) to fenbendazole (FBZ), a commonly used treatment.
• They conducted the research on two horse farms in central Italy known to have a history of FBZ resistance.
• A Faecal Egg Count Reduction Test was conducted pre- and post-treatment of horses on these farms to evaluate their susceptibility to FBZ, as well as two other alternative treatments – oxibendazole and moxidectin.
• A Reverse Line Blot (RLB) assay was used to molecularly examine faecal eggs and accurately identify specific cyathostome species.

Findings

• The research confirmed that resistance to FBZ was prevalent on both study farms.
• Alternatively, both oxibendazole and moxidectin showed high success rates as treatment methods, with effectiveness of 97% and 100% respectively.
• The RLB assay identified eight cyathostome species in samples taken before treatment, with two species found to be present even after FBZ treatment.
• Additionally, two species were found to be less than 100% susceptible to oxibendazole.

Implications and Conclusions

• These findings confirmed that resistance to the benzimidazoles class of wormers (which includes FBZ) is established in cyathostome populations from horse farms in Italy.
• It was found that these worm populations are, however, susceptible to treatment with moxidectin.
• Oxibendazole was found to be effective for the first time against Italian populations of cyathostomes resistant to other treatments from the same class (benzimidazoles).
• The RLB assay proved to be a useful tool in studying the distribution of these parasitic populations at the species level under actual field conditions, indicating it could serve a role in broader investigations of drug resistance in horse farms in multiple countries.