Effectiveness of Anthelmintic Treatments in Small Ruminants in Germany

Abstract

Widespread anthelmintic resistance is a concern for small ruminant health and production worldwide. The current situation regarding anthelmintic efficacy is, however, not very well studied in Germany. Thus, a nationwide field study was undertaken to assess the effectiveness of 253 treatments performed in 223 small ruminant flocks by faecal egg count reduction test (FECRT) using pooled samples and a modified McMaster method. The percentage of Haemonchus contortus and non-Haemonchus eggs was determined by fluorescence microscopy following peanut agglutinin-fluorescein isothiocyanate staining. Treatments were chosen and performed by farmers together with their local veterinarian, and potentially confounding factors for FECRT results were addressed as far as possible by rigorous inclusion criteria. Reduced effectiveness was observed for treatments with all examined anthelmintic classes, but treatments with benzimidazoles and moxidectin showed significantly poorer results than monepantel, a closantel and mebendazole combination, and levamisole. Low case numbers precluded reliable assessment of avermectins. Unsuccessful treatments were frequently associated with the survival of H. contortus, but this was also observed for non-Haemonchus genera. The results are highly concerning, and sustainable approaches to parasite control are urgently needed to prevent further deterioration of this situation.

Keywords: anthelmintic efficacy; avermectins; benzimidazoles; closantel; faecal egg count reduction test; goats; levamisole; monepantel; moxidectin; sheep.

Figure 1

Faecal egg count reduction (FECR) following 253 anthelmintic treatments (sheep: 218; goats: 35) performed in 223 small ruminant flocks (sheep: 193; goats: 30), and paired comparison between anthelmintic categories. n = number of flocks using anthelmintic category; MOX = moxidectin; AV = avermectins, LEV = levamisole; MOP = monepantel; BZ = benzimidazoles; CLOS + BZ = closantel and mebendazole combination product; X²_{Kruskal-Wallis}(5) = Kruskal–Wallis chi-squared statistics with the degrees of freedom, ε²_ordinal = effect size with CI_95% = 95% confidence intervals for the effect size; n_obs = number of observations. Interpretation of ε²_ordinal = 0.16: large effect size [44]. Explanation of scientific notation for p-values: 1.05e-06 is equivalent to p < 0.001.

Figure 2

Predicted probabilities of faecal egg count reduction (FECR) in sheep for the various anthelmintic categories, with error bars indicating the 95% confidence interval. MOX = moxidectin; AV = avermectins, LEV = levamisole; MOP = monepantel; BZ = benzimidazoles; CLOS + BZ = closantel and mebendazole.

Figure 3

Paired comparison of the pre- and post-treatment percentage of Haemonchus contortus eggs for treatments performed in sheep, by anthelmintic category. This analysis included all ovine treatments irrespective of their classification as successful or unsuccessful. MOX = moxidectin; AV = avermectins, LEV = levamisole; MOP = monepantel; BZ = benzimidazoles; CLOS + BZ = closantel and mebendazole; n = number of flocks treated per category with available paired results. r^rank_biserial = effect size with CI_95% = 95% confidence interval; n_pairs = number of paired results. Interpretation of r^rank_biserial: < 0.05: tiny; ≥0.05 and <0.1: very small; ≥0.1 and <0.2: small; ≥0.2 and <0.3: medium; ≥0.3 and <0.4: large; ≥0.4: very large [45]. Explanation of scientific notation for p-values: 3.46e-05 and 7.33e-04 are both equivalent to p < 0.001; 1.09e-03 is equivalent to p = 0.001.

Figure 4

Paired comparison of the pre- and post-treatment percentage of non-Haemonchus strongyle eggs for treatments performed in sheep, by anthelmintic category. This analysis included all ovine treatments irrespective of their classification as successful or unsuccessful. MOX = moxidectin; AV = avermectins, LEV = levamisole; MOP = monepantel; BZ = benzimidazoles; CLOS + BZ = closantel and mebendazole; n = number of flocks treated per category with available paired results. r^rank_biserial = effect size with CI_95% = 95% confidence interval; n_pairs = number of paired results. Interpretation of r^rank_biserial: <0.05: tiny; ≥0.05 and <0.1: very small; ≥0.1 and <0.2: small; ≥0.2 and <0.3: medium; ≥0.3 and <0.4: large; ≥0.4: very large [45]. Explanation of scientific notation for p-values: 4.61e-10, 1.20e-04, 2.76e-04 and 3.83e-06 are all equivalent to p < 0.001.

Figure 5

Paired comparison of the pre- and post-treatment percentage of H. contortus eggs for treatments performed in goats, by anthelmintic category. This analysis included all caprine treatments irrespective of their classification as successful or unsuccessful. MOX = moxidectin; BZ = benzimidazoles; n = number of flocks treated per category with available paired results. r^rank_biserial = effect size with CI_95% = 95% confidence interval; n_pairs = number of paired results. Interpretation of r^rank_biserial: <0.05: tiny; ≥0.05 and < 0.1: very small; ≥0.1 and <0.2: small; ≥0.2 and <0.3: medium; ≥0.3 and <0.4: large; ≥0.4: very large [45].

Figure 6

Paired comparison of the pre- and post-treatment percentage of non-Haemonchus strongyle eggs for treatments performed in goats, by anthelmintic category. This analysis included all caprine treatments irrespective of their classification as successful or unsuccessful. MOX = moxidectin; BZ = benzimidazoles; n = number of flocks treated per category with available paired results. r^rank_biserial = effect size with CI_95% = 95% confidence interval; n_pairs = number of paired results. Interpretation of r^rank_biserial: < 0.05: tiny; ≥0.05 and <0.1: very small; ≥0.1 and <0.2: small; ≥0.2 and <0.3: medium; ≥0.3 and <0.4: large; ≥0.4: very large [45]. Explanation of scientific notation for p-values: 6.70e-03 is equivalent to p = 0.007.