Impaired efficacy of fenbendazole and ivermectin against intestinal nematodes in adult horses in Iran

This study aimed to evaluate the efficacy of fenbendazole and ivermectin on strongyles and Parascaris sp. infecting adult riding horses in three regions with different climates. During 2021 and 2022 fecal specimens were randomly collected from 483 horses older than three years in 31 equestrian clubs in Hamedan (n = 217), Yazd (n = 146) and Tabriz cities (n = 120). Eggs were counted by McMaster technique, and the strongyle larvae were identified using coproculture, PCR and sequencing. Horses with strongyles and Parascaris egg counts ≥150 were enrolled in fecal egg count reduction (FECR) examination following treatment with ivermectin or fenbendazole. In total, 26.5% of examined horses were positive with at least one parasite. Infection rates varied in three cities i.e., 25.8% in Hamedan, 28.8% in Yazd, 25% in Tabriz. Fifty-seven horses had FECR measured. FECR below <90% was observed for IVM-strongyle in two horses in Tabriz, for FBZ-strongyle in two horses in Tabriz and two horses in Hamedan, for IVM-Parascaris in one horse in all three cities, and for FBZ-Parascaris in one horse in Yazd. Furthermore, FECR 90-100% was observed in IVM-Parascaris and FBZ -Parascaris groups in Tabriz. Data herein presented demonstrate different degrees of resistance of strongyles and Parascaris infecting horses in Iran against both ivermectin and fenbendazole. Since non-principled use of anthelminthics is common among horse owners, urgency of test-and-treatment strategy should be educated and implemented by policy-making organizations. Evaluating efficacy of different anthelminthics and choosing the most effective treatment in each region is suggested.

Evaluation and Correlation of Multiple Anthelmintic Resistances to Gastrointestinal Nematodes Using Different Fecal Egg Count Reduction Methods in Small Ruminants of Punjab, India

PURPOSE

Concordance of multiple anthelmintic resistances for gastrointestinal nematodes in small ruminants by three average-based and two individually based fecal egg count reduction (FECR) tests was evaluated and corrected.

METHODS

Sheep and goats (≥ 8 weeks) from five farms were randomly assigned to three treatment groups (I, II, III; n = 10 per group) and one untreated control group (Group IV; n = 10). Group I received fenbendazole at the dose rate of 5 and 10 mg/kg, Group II received ivermectin at the dose rate of 0.2 and 0.4 mg/kg, and Group III received levamisole at the dose rate of 8 and 12 mg/kg body weight orally for sheep and goat, respectively. Three average-based methods of FECR (FECR₁, FECR₂ and FECR₃) and two individually based methods of FECR (iFECR₁ and iFECR₂) were evaluated.

RESULTS

For fenbendazole resistance, Spearman correlation coefficient for FECR₁ was non-significant with other formulae, but for FECR₂ with FECR₃, FECR₃ with iFECR₁ and iFECR₁ with iFECR₂ coincidence was significant at 1%, while for FECR₂ with iFECR₂ and FECR₃ with iFECR₂ it was significant at 5%. Spearman correlation coefficients for ivermectin resistance were significant at 1% level and for levamisole it showed significant coincidence at 1% for FECR₁ with FECR₂ and iFECR₁, FECR₂ with FECR₃ and iFECR₁, and iFECR₁ with iFECR₂, while for FECR₁ with FECR₃ and iFECR₂ coincidence was significant at 5% level. Concordance of kappa values indicated that the coincidence of the prevalence of anthelmintic resistance (95% CI) among the five farms was non-significant.

CONCLUSIONS

Concordance between the standard average-based FECR and individually based methods suggests that either method could be applied to small ruminant farms.