title: Minimising the development of anthelmintic resistance, and optimising the use of the novel anthelmintic monepantel, for the sustainable control of nematode parasites in Australian sheep grazing systems.
abstract: OBJECTIVE
  To compare the risk of different treatment scenarios on selecting for anthelmintic resistance on Australian sheep farms.
  
  
  METHODS
  A computer simulation model predicted populations of Trichostrongylus colubriformis, Haemonchus contortus or Teladorsagia (Ostertagia) circumcincta, and the frequency of anthelmintic resistance genes.
  
  
  METHODS
  Nematode populations and the progression of drug resistance for a variety of treatment options and management practices in sheep-rearing areas of Western Australia (WA), Victoria (VIC) and New South Wales (NSW) were simulated. A scoring system was devised to measure the success of each option in delaying resistance to each anthelmintic and in controlling nematode populations.
  
  
  RESULTS
  The best option at all sites was combining the new anthelmintic (monepantel) with a triple mixture of benzimidazole, levamisole and abamectin (COM). The next best option was: in NSW, rotation at each treatment between monepantel, moxidectin and COM; in VIC, rotation at each treatment between monepantel and COM; and in WA, rotation at each treatment between monepantel (used in winter) and COM or moxidectin (used in summer-autumn). In WA, rapid selection for resistance occurred as a consequence of summer-autumn treatments; however, if a small percentage of adult stock were left untreated then this selection could be greatly reduced. Despite purposely assuming relatively high resistance to benzimidazole and levamisole, COM was still effective in controlling worms and delaying resistance.
  
  
  CONCLUSIONS
  Because of cost constraints, it may not be feasible or profitable for producers to always use the combination of all drugs. However, the second- and third-best options still considerably slowed the development of anthelmintic resistance.
authors.affiliation: School of Veterinary & Biomedical Sciences, Murdoch University, Murdoch, Western Australia 6150, Australia. R.Dobson@murdoch.edu.au
authors.forename: R J
authors.initials: RJ
authors.lastname: Dobson
authors.forename: B C
authors.initials: BC
authors.lastname: Hosking
authors.forename: R B
authors.initials: RB
authors.lastname: Besier
authors.forename: S
authors.initials: S
authors.lastname: Love
authors.forename: J W A
authors.initials: JW
authors.lastname: Larsen
authors.forename: P F
authors.initials: PF
authors.lastname: Rolfe
authors.forename: J N
authors.initials: JN
authors.lastname: Bailey
mesh_terms: D000607:Aminoacetonitrile / Q000031:analogs & derivatives* / Q000494:pharmacology; D000822:Animal Husbandry / Q000379:methods; D000818:Animals; D000871:Anthelmintics / Q000494:pharmacology*; D001315:Australia; D001562:Benzimidazoles / Q000494:pharmacology; D004351:Drug Resistance; D018432:Drug Resistance, Multiple; D004359:Drug Therapy, Combination; D005260:Female; D006374:Helminthiasis, Animal / Q000188:drug therapy* / Q000453:epidemiology / Q000469:parasitology; D007559:Ivermectin / Q000031:analogs & derivatives / Q000494:pharmacology; D007978:Levamisole / Q000494:pharmacology; D008297:Male; D012756:Sheep; D012757:Sheep Diseases / Q000188:drug therapy* / Q000453:epidemiology / Q000469:parasitology; D016896:Treatment Outcome
chemical_list: D000871:Anthelmintics; D001562:Benzimidazoles; D007978:Levamisole; D000607:Aminoacetonitrile; C048324:abamectin; D007559:Ivermectin; C533978:monepantel; C031000:benzimidazole