Efficacy of moxidectin against internal parasites of sheep.

The efficacy of injectable and oral formulations of moxidectin, at a dosage of 0.2 mg kg -1 live mass was evaluated by the non-parametric method (NPM) against the most common internal parasites of sheep in 9 trials involving a total of 201 sheep. Both formulations obtained an A classification (more than 80% effective in more than 80% of the treated animals) against the third (L3) and fourth (L4) larval and adult stages of Haemonchus contortus, Teladorsagia circumcineta, Trichostrongylus colubriformis, Gaigeria pachyscelis, Chabertia ovina, Oesophagostomum columbianum and Dictyocaulus filaria, and L3 Nematodirus spathiger. The injectable formulation was similarly effective against L4 Strongyloides papillosus and the oral formulation against L4 N. spathiger and adult S. papillosus and N. spathiger. In contrast, a B classification (more than 60% effective in more than 60% of the treated animals) was obtained by the oral formulation against L4 of S. papillosus and by the injectable formulation against L4 and adult N. spathigher. Both formulations were ineffective against L3 S. papillosus, and the oral formulation also against the adults of this species.

Efficacy of moxidectin against a strain of Haemonchus contortus resistant to ivermectin, a benzimidazole and a salicylanilide.

The efficacy of moxidectin at 0.2 mg kg-1 live body mass against the multiple anthelmintic resistant White River Krtz strain of H. contortus was determined and compared to that of ivermectin, a benzimidazole, a salicylanilide and levamisole. Moxidectin and levamisole were effective against this strain of H. contortus and reduced the arithmetic mean burdens of this parasite in the sheep by 99.98% and 99.59%, respectively, while the efficacy of ivermectin, albendazole and closantel was only 29.1%, 33.75% and 78.3%, respectively.