Total Failure of Fenbendazole to Control Strongylid Infections in Czech Horse Operations.
Authors: Nápravníková Jana, Várady Marián, Vadlejch Jaroslav
Journal: Frontiers in veterinary science
Summary
# Editorial Summary: Anthelmintic Resistance in Czech Horse Operations Anthelmintic resistance in equine strongylids has reached critical levels in the Czech Republic, with fenbendazole—once a cornerstone of parasite control—now completely ineffective across all tested operations. Researchers evaluated the efficacy of four commonly used anthelmintics on 48 horse operations meeting clinical infection thresholds, conducting 969 faecal egg count reduction tests and analysing results using Bayesian hierarchical models to determine both individual operation-level resistance and broader population efficacy patterns. Whilst ivermectin and moxidectin retained excellent efficacy (>99% in most operations), fenbendazole failed catastrophically, achieving only 19–78% efficacy across all 18 operations tested, with the alarming finding that 29% of treatments resulted in higher post-treatment egg counts than baseline. Pyrantel embonate showed intermediate problems, demonstrating adequate efficacy in only 15 of 22 operations tested, with suspected resistance developing in seven operations. For equine professionals in the UK and Europe, these findings underscore the urgency of moving away from benzimidazole reliance, implementing rotational strategic dosing protocols with macrocyclic lactones, conducting regular faecal testing to guide treatment decisions, and exploring non-chemical control measures to preserve remaining anthelmintic options.
Read the full abstract on PubMed
Practical Takeaways
- •Do not use fenbendazole for strongylid control in Czech operations—it has completely failed and may paradoxically increase parasite burdens in nearly 30% of cases.
- •Ivermectin and moxidectin remain highly effective options, though practitioners should monitor for emerging resistance and rotate between drug classes to slow further resistance development.
- •Implement targeted parasite control strategies beyond single-drug reliance: consider combination therapies, strategic timing of treatments, and regular fecal egg count monitoring to detect resistance early.
Key Findings
- •Fenbendazole showed complete failure across all 18 operations tested, with FECR ranging from 19.1-77.8% and 29.1% probability of negative efficacy (post-treatment counts exceeding pre-treatment).
- •Ivermectin and moxidectin demonstrated excellent efficacy (FECR 99.8-100% and 99.4-100% respectively) in 45 and 23 operations, maintaining effectiveness across the tested horse operations.
- •Pyrantel embonate showed sufficient efficacy in 15 operations but suspected resistance in 7 operations (FECR 88.1-99.1%), indicating emerging resistance patterns.
- •The study of 48 Czech horse operations with 969 fecal egg count reduction tests revealed widespread anthelmintic resistance requiring urgent intervention in parasite control strategies.