Benzimidazole resistance of equine strongyles: critical tests of several classes of compounds against population B strongyles from 1977 to 1981.

The research paper discusses a study conducted between 1977 and 1981 that evaluated the effectiveness of several drugs on strongyles, a kind of parasitic worm, in horses. The study found varying levels of success with each compound, indicating some forms of resistance to certain drugs among different species of the parasite.

Methodology

• The study was carried out on a random population of 10 horses naturally infected with Population B strongyles, a type of parasitic worm that affects the intestine.
• A variety of compounds were tested, including oxibendazole, albendazole, a combination of thiabendazole and trichlorfon, a mixture of thiabendazole with piperazine, febantel at various doses, and pyrantel pamoate.

Findings

• Large strongyles, namely Strongylus vulgaris (present in 9 of the horses) and Strongylus edentatus (found in 5 horses), were successfully eliminated by each compound and mixture. The removal of these strongyles was deemed 100% effective.
• Five species of small strongyles, which had previously demonstrated resistance to 5 different benzimidazoles (a class of antiparasitic drugs), were thoroughly removed by Oxibendazole, Albendazole, the mixture of TBZ and Piperazine, Febantel (at 24mg/kg), and Pyrantel Pamoate.
• However, these 5 species appeared resistant to a smaller dose of Febantel (6mg/kg) in 3 of the experiment’s horse foals. A small strongyle, Cylicostephanus minutus, was also found to be resistant to the same dosage of Febantel in 2 out of 3 foals.
• When the dosage of Febantel was increased to 12mg/kg, the average removal of these resistant species increased to 88%.
• The effectiveness of the mixture of thiabendazole and trichlorfon varied between the species. It was generally ineffective against Cyathostomum catinatum, Cyathostomum coronatum, and Cylicostephanus longibursatus, but showed high efficacy (86-99%) against Cylicocyclus nassatus and Cylicostephanus goldi.

Significance

• This study gives a valuable insight into the resistance of different species of strongyles to different drugs. The varying results suggest that treatment outcomes may depend on the specific species of strongyle present, as well as the choice and dosage of the drug.
• The findings carry potentially important implications for the treatment of strongyle infections in horses. They highlight the importance of understanding specific species-drug interactions to improve parasitic resistance management strategies.