The prevalence of anthelmintic resistance of horse strongyles in The Netherlands.

The article explores the prevalence of anthelmintic resistance among horse strongyles in The Netherlands by testing the effectiveness of three common anthelmintic drugs: cambendazole, pyrantel pamaote and ivermectin. The research indicates that benzimidazole resistance, especially, is widespread and common, suggesting these class of drugs should be excluded for strategic use in horses.

Research Methodology

• In conducting the study, a total of 616 horses from 22 different farms were subjected to the survey. The study utilized egg count reduction tests as a primary method of determining the effectiveness of the drugs.
• Three commonly used anthelmintic drugs were selected for the test: cambendazole, pyrantel pamaote and ivermectin. These drugs were chosen due to their widespread use in the treatment of parasitic worms in horses.

Findings of the Study

• The efficacy of the drugs varied widely: cambendazole exhibited a wide range of effectiveness between 0% and 93%, and pyrantel’s effectiveness ranged from 93% to 100%. In stark contrast, ivermectin treatments were found to be 100% effective on all farms.
• Larval cultures were examined after the treatments: those after cambendazole treatments consisted exclusively of cyathostome larvae, a common type of parasitic roundworm in horses. Following pyrantel treatments, a mix of cyathostome and other larvae were observed. However, only a few cyathostome larvae were noted after ivermectin treatments.

Conclusion

• The results suggest that resistance to benzimidazoles (chemical class of cambendazole) among cyathostomes is very common and widespread in The Netherlands. Due to this prevalence in resistance, the class of drugs known as benzimidazoles, including pro-benzimidazoles, are recommended to be excluded for strategic use in horses. This means that other anthelmintic drugs should be preferred in regular parasite control programs for horses in the region.