title: Reduction of benzimidazole resistance in established Haemonchus contortus populations in goats using a single infection with a benzimidazole-susceptible isolate.
abstract: An in vivo study in goats evaluated the effect of superimposing a single artificial infection with a benzimidazole (BZ)-susceptible Haemonchus contortus isolate upon established H. contortus populations of known BZ resistance by measuring the phenotypic BZ resistance of eggs collected from faeces before and after re-infection. Two H. contortus isolates, one benzimidazole resistant (BZR) and the other susceptible (BZS), were used to infect worm-free goats. Eight goats were initially infected with 2000 third-stage larvae (L3). In each case the inoculum contained a pre-determined proportion of the two isolates: 100% BZS (one goat), 75% BZS/25% BZR (two goats), 50% BZS/50% BZR (two goats), 25%BZS/75% BZR (two goats) and, finally, 100% BZR (one goat). The phenotypic BZ susceptibility of the H. contortus population formed in each goat after the first infection was determined on days 30 and 36 post-infection using an egg-hatch assay (EHA) that estimated the concentration of thiabendazole (TBZ) required for 95% inhibition of larval hatching (EC(95)) with a 95% confidence interval (95% CI). On day 49 post-infection, goats were re-infected with 2000 L3 of the BZS isolate alone. A second set of EHA bioassays was performed 28 days and 34 days after re-infection. The first infection protocol produced three populations classified as BZS (EC(95) 0.055-0.065 μg TBZ/ml) while four were categorized as BZR (EC(95) 0.122-0.344 μg TBZ/ml). The status of one other population could not be determined. After re-infection with BZS L3, the number of susceptible populations increased to six (EC(95) 0.043-0.074 μg TBZ/ml) while the remaining two were deemed resistant (EC(95) 0.114-119 μg TBZ/ml). Re-infection with BZS L3 thereby reduced the resistance status of most H. contortus populations.
authors.affiliation: Campus de Ciencias Biológicas y Agropecuarias, FMVZ, Universidad Autónoma de Yucatán,Km 15.5 Carretera Mérida-Xmatkuil,Mérida,Yucatán,México.
authors.forename: J I
authors.initials: JI
authors.lastname: Chan-Pérez
authors.affiliation: Campus de Ciencias Biológicas y Agropecuarias, FMVZ, Universidad Autónoma de Yucatán,Km 15.5 Carretera Mérida-Xmatkuil,Mérida,Yucatán,México.
authors.forename: J F J
authors.initials: JF
authors.lastname: Torres-Acosta
authors.affiliation: Campus de Ciencias Biológicas y Agropecuarias, FMVZ, Universidad Autónoma de Yucatán,Km 15.5 Carretera Mérida-Xmatkuil,Mérida,Yucatán,México.
authors.forename: R I
authors.initials: RI
authors.lastname: Rodríguez-Vivas
authors.affiliation: Campus de Ciencias Biológicas y Agropecuarias, FMVZ, Universidad Autónoma de Yucatán,Km 15.5 Carretera Mérida-Xmatkuil,Mérida,Yucatán,México.
authors.forename: S L
authors.initials: SL
authors.lastname: Villegas-Pérez
mesh_terms: D000818:Animals; D000871:Anthelmintics / Q000008:administration & dosage*; D001562:Benzimidazoles / Q000008:administration & dosage*; D004351:Drug Resistance; D005243:Feces / Q000469:parasitology; D005260:Female; D015511:Goat Diseases / Q000188:drug therapy / Q000469:parasitology*; D006041:Goats; D006188:Haemonchiasis / Q000188:drug therapy / Q000469:parasitology / Q000662:veterinary*; D006189:Haemonchus / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology; D007814:Larva / Q000187:drug effects / Q000235:genetics / Q000502:physiology
chemical_list: D000871:Anthelmintics; D001562:Benzimidazoles; C031000:benzimidazole