title: Characterisation of an avermectin resistant strain of Australian Haemonchus contortus.
abstract: A strain of Haemonchus contortus (CAVR) isolated in Australia was found to be resistant to ivermectin (IVM) with 0.4 mg kg-1 of the anthelmintic failing to significantly reduce worm burdens. Resistance to IVM was sex-influenced in the CAVR strain with adult males showing a greater sensitivity to IVM. Cross resistance to moxidectin was evident with approximately 15% of the population surviving a dose of 0.1 mg kg-1. The free-living stages of the CAVR isolate had a reduced sensitivity to avermectin (AVM) inhibition of development and motility. Similar structure-activity patterns and resistance factors were obtained for a series of related AVMs as inhibitors of larval development and L3 motility in CAVR and White River II, an IVM-resistant H. contortus isolate from South Africa. Further, both isolates were found to be 3 times more sensitive to paraherquamide than a susceptible H. contortus isolate. This suggest that the same resistance mechanism is operating in both isolates. The CAVR strain is susceptible to the benzimidazoles, levamisole and closantel.
authors.affiliation: C.S.I.R.O. Division of Animal Health, Pastoral Research Laboratory, Armidale, N.S.W., Australia.
authors.forename: L F
authors.initials: LF
authors.lastname: Le Jambre
authors.forename: J H
authors.initials: JH
authors.lastname: Gill
authors.forename: I J
authors.initials: IJ
authors.lastname: Lenane
authors.forename: E
authors.initials: E
authors.lastname: Lacey
mesh_terms: D000818:Animals; D000871:Anthelmintics / Q000494:pharmacology* / Q000627:therapeutic use; D000900:Anti-Bacterial Agents / Q000494:pharmacology / Q000627:therapeutic use; D001315:Australia; D001562:Benzimidazoles / Q000494:pharmacology; D004351:Drug Resistance; D004359:Drug Therapy, Combination; D005260:Female; D006188:Haemonchiasis / Q000188:drug therapy / Q000469:parasitology / Q000662:veterinary*; D006189:Haemonchus / Q000187:drug effects* / Q000302:isolation & purification; D007559:Ivermectin / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use; D007978:Levamisole / Q000494:pharmacology / Q000627:therapeutic use; D018942:Macrolides; D008297:Male; D012458:Salicylanilides / Q000494:pharmacology / Q000627:therapeutic use; D012756:Sheep; D012757:Sheep Diseases / Q000188:drug therapy / Q000469:parasitology*
chemical_list: D000871:Anthelmintics; D000900:Anti-Bacterial Agents; D001562:Benzimidazoles; D018942:Macrolides; D012458:Salicylanilides; D007978:Levamisole; D007559:Ivermectin; C019264:avermectin; C023342:closantel; C027837:moxidectin