title: Selection for resistance to macrocyclic lactones by Haemonchus contortus in sheep.
abstract: An anthelmintic-sensitive Haemonchus contortus strain was selected for moxidectin and ivermectin resistance concurrently for 22 generations. Treatment with 0.002 mg moxidectin/kg BW or 0.02 mg ivermectin/kg BW produced >99% efficacy against the susceptible parent strain passaged for 22 generations without any anthelmintic exposure. However, to obtain similar efficacy the moxidectin-selected and the ivermectin-selected strains of H. contortus required 0.05 mg moxidectin/kg BW or 0.4 mg ivermectin/kg BW. These results indicate that development of resistance to one macrocyclic lactone, simultaneously results in resistance to another macrocyclic lactone. However, rates of resistance development differ between compounds and occurs more slowly with moxidectin than with ivermectin.
authors.affiliation: Fort Dodge Animal Health, PO Box 5366, Princeton, NJ 08543, USA. ranjans@pt.fdah.com
authors.forename: S
authors.initials: S
authors.lastname: Ranjan
authors.forename: G T
authors.initials: GT
authors.lastname: Wang
authors.forename: C
authors.initials: C
authors.lastname: Hirschlein
authors.forename: K L
authors.initials: KL
authors.lastname: Simkins
mesh_terms: D000818:Animals; D000871:Anthelmintics / Q000494:pharmacology* / Q000627:therapeutic use; D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000627:therapeutic use; D004351:Drug Resistance; D005260:Female; D006188:Haemonchiasis / Q000188:drug therapy / Q000662:veterinary*; D006189:Haemonchus / Q000187:drug effects* / Q000254:growth & development; D007559:Ivermectin / Q000494:pharmacology* / Q000627:therapeutic use; D018942:Macrolides; D008297:Male; D021261:Parasitic Sensitivity Tests / Q000662:veterinary; D011897:Random Allocation; D012641:Selection, Genetic; D012680:Sensitivity and Specificity; D012756:Sheep; D012757:Sheep Diseases / Q000188:drug therapy* / Q000469:parasitology
chemical_list: D000871:Anthelmintics; D000900:Anti-Bacterial Agents; D018942:Macrolides; D007559:Ivermectin; C027837:moxidectin