Characterisation of milbemycin-, avermectin-, imidazothiazole- and benzimidazole-resistant Teladorsagia circumcincta from a sheep flock

N. D. Sargison, F. Jackson, David Wilson, D. J. Bartley, C. D. Penny, J. S. Gilleard

Research output: Contribution to journalArticlepeer-review

Abstract

Selection for milbemycin resistance in a population of Teladorsagia circumcincta was examined in a sheep flock in which a lack of persistence of an oral dose of 0.2 mg/kg moxidectin against T circumcincta had previously been identified. A faecal egg count reduction test also showed resistance to benzimidazole, levamisole and avermectin anthelmintic groups. Bioassays were used to compare the moxidectin-resistant T circumcincta with another previously characterised benzimidazole-, levamisole- and ivermectin-resistant (MTci5) strain that had been isolated from a sheep flock in the same region in south-east Scotland and with an anthelmintic-susceptible (MTci3) strain of T circumcincta. The mean ED50 value (the concentration of drug required to prevent 50 per cent of eggs from hatching) obtained for thiabendazole in egg hatch assays was higher in the moxidectin-resistant T circumcincta than in the ivermectin-resistant MTci5 strain. The inclusion of the cytochrome p450 inhibitor piperonyl butoxide in larval feeding inhibition assays increased the level of ivermectin resistance in vitro in the ivermectin- and moxidectin-resistant populations, but not in the ivermectin-susceptible MTci3 strain of T circumcincta.

Original languageEnglish
Pages (from-to)681-686
Number of pages6
JournalVeterinary Record
Volume166
Issue number22
DOIs
Publication statusPublished - 29 May 2010

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