Resistance to benzimidazole anthelmintics in equine strongyles. 2. Evidence of side-resistance, and susceptibility of benzimidazole-resistant strongyles to non-benzimidazole compounds.

This study investigates the resistance of small strongyles, a type of parasite found in horses, to various anthelmintics (worming drugs). The researchers found that thiabendazole-resistant strongyles responded well to non-benzimidazole drugs and also to a certain combination of benzimidazole compounds. However, other benzimidazole drugs showed less effectiveness.

Methodology of the Study

• This research involved multiple studies testing the effectiveness of different anthelmintic drugs on horses infected with thiabendazole-resistant small strongyles. The strongyles are parasites in the family of Cyathostominae.
• In each study, the horses were divided into groups and treated with different anthelmintics. The drugs used included both benzimidazole and non-benzimidazole types, as well as their combinations.
• The effectiveness of each treatment was evaluated based on the reduction in faecal strongyle egg counts 20 days post-treatment.

Key Findings

• The first study found that treatment with morantel tartrate, a non-benzimidazole anthelmintic, and a combination of thiabendazole, piperazine and trichlorphon produced significant reductions in strongyle egg counts.
• In contrast, treatment with mebendazole, febantel, and febantel plus trichlorphon—all benzimidazole anthelmintics—did not significantly decrease strongyle egg counts.
• When treatments failed, small strongyles of the sub-family Cyathostominae were always found to be involved.
• In a subsequent study, treatment with either morantel tartrate or haloxon (another non-benzimidazole anthelmintic) were also proved efficient in reducing faecal strongyle egg counts.
• In the final study, treatments with oxibendazole, piperazine, and combinations of benzimidazole and piperazine were found to significantly reduce faecal strongyle egg counts.
• On their own, most benzimidazole anthelmintics failed to significantly reduce these counts. The one exception was with oxibendazole.

Conclusion

• The study concluded that thiabendazole-resistant small strongyles were susceptible to certain non-benzimidazole anthelmintics and to a combination of certain benzimidazole compounds.
• The research also confirmed that there was no increase in benzimidazole resistance level as a result of drug treatment over one generation.

This research provides valuable insight into the resistance characteristics of these parasites and the effectiveness of different treatment strategies. It helps suggest more effective treatment options for horses infected with benzimidazole-resistant strongyles.