Re: Macrocyclic lactone resistance in sheep

Authors: Murphy A
Publication: New Zealand Veterinary Journal, Volume 49, Issue 4, pp 165-166, Aug 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: Macrocyclic lactone resistance in sheep. Leathwick and Sutherland (2001) endorse the concept raised in my letter (Murphy, 2001) that the use of some macrocyclic lactones could delay the onset of anthelmintic resistance to the action group when compared with other members of the group, but claim that I failed to adequately address 2 important issues: a) that I failed to apply the same calculations to abamectin that I used for moxidectin and; b) that I failed to recognise the implications of the persistent nature of moxidectin. With regard to the first issue: the efficacy of moxidectin against ivermectin-resistant parasites is well documented (Craig et al, 1992; Pankavich et al, 1992; Pomroy et al, 1992; Oosthuizen and Erasmus, 1993; Leathwick et al, 2000; Vickers et al, 2001) but there is relatively little information on the efficacy of abamectin against ivermectin-resistant parasites. Leathwick et al (2000) demonstrated that abamectin was 96% effective against a 23-day-old infection of an ivermectin-resistant strain of Ostertagia circumcincta. Moxidectin was 99.9% effective in the same trial and would therefore control more than 95% of the worms left behind by abamectin. Other authors have….

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