Re: Ivermectin-resistant Ostertagia circumcincta from sheep in the lower North Island and their susceptibility to other macrocyclic lactone anthelmintics

Authors: Murphy A
Publication: New Zealand Veterinary Journal, Volume 49, Issue 3, pp 122-123, Jun 2001
Publisher: Taylor and Francis

Animal type: Livestock, Production animal, Ruminant, Sheep
Subject Terms: Alimentary system/gastroenterology, Animal remedies/veterinary medicines, Anthelmintics, Parasite control, Parasites - internal, Nematode, Treatment/therapy
Article class: Correspondence

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Abstract: Correspondence: Re: Ivermectin-resistant Ostertagia circumcinta from sheep in the lower North Island and their susceptibility to other macrocyclic lactone anthelmintics. Leathwick et al (2000) examined the efficacy of 3 macrocyclic lactone anthelmintics against a 23-day-old infection with an ivermectin-resistant strain of Ostertagia circumcincta. The efficacy of moxidectin against this strain was 99.9-100%. The efficacy of abamectin, at 92-96%, was higher than the efficacy of ivermectin but less than that of moxidectin. In their discussion, Leathwick et al (2000) did not differentiate the efficacy of moxidectin and abamectin and there are no probability statistics included in the paper. However, analysis of the results provided using log transformed data demonstrates that the difference between counts in lambs treated with moxidectin and lambs treated with abamectin is significant (p=0.02). This difference suggests that moxidectin would be 95.7% (geometric mean) to 97.7% (arithmetic mean) effective against the worms left behind by abamectin. The efficacy of moxidectin against ivermectin-resistant parasites is well documented…

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