title: Substitution of benzimidazole-resistant nematodes for susceptible nematodes in grazing lambs.
abstract: Multi-drug-resistant gastrointestinal nematode parasite populations are becoming more and more prevalent. Since anthelmintic treatments are of limited effectiveness, one solution could be to replace the anthelmintic-resistant population by a susceptible population, in order to re-establish the possibility of drug-based anthelmintic control. We investigated this substitution strategy in 4 paddocks of 0.7 ha, each of which was seeded with a benzimidazole-resistant Teladorsagia circumcincta population. The proportion of benzimidazole-resistant worms in these paddocks ranged from 20% to 89%. A 2-step replacement was performed: first, the paddocks were not grazed for 6 months (from December to July), and then the grass was cut to eliminate any residual infective larvae, before contaminating each of the paddocks with 10 seeder lambs experimentally infected with a benzimidazole-susceptible strain of T. circumcincta (from July to November). At the end of the experiment, all the populations on the 4 paddocks were phenotypically benzimidazole-susceptible, but genotyping indicated that 2 populations harboured 1% and 3% resistant worms respectively. This study demonstrates that nematode replacement is feasible in temperate areas, using semi-intensive stock management, even when the initial levels of benzimidazole-resistance are very high. Further research should next assess replacing the whole community to cope with the species diversity observed under field conditions.
authors.affiliation: INRA, UR1282 Animal Infectious Diseases and Public Health, F-37380 Nouzilly, France.
authors.forename: M-N
authors.initials: MN
authors.lastname: Moussavou-Boussougou
authors.forename: A
authors.initials: A
authors.lastname: Silvestre
authors.forename: J
authors.initials: J
authors.lastname: Cortet
authors.forename: C
authors.initials: C
authors.lastname: Sauve
authors.forename: J
authors.initials: J
authors.lastname: Cabaret
mesh_terms: D000818:Animals; D000871:Anthelmintics / Q000494:pharmacology*; D001562:Benzimidazoles / Q000494:pharmacology*; D004351:Drug Resistance / Q000502:physiology*; D005838:Genotype; D009348:Nematoda / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D009349:Nematode Infections / Q000469:parasitology / Q000662:veterinary*; D012756:Sheep; D012757:Sheep Diseases / Q000469:parasitology*
chemical_list: D000871:Anthelmintics; D001562:Benzimidazoles; C031000:benzimidazole