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: J I Chan-Pérez, J F J Torres-Acosta, R I Rodríguez-Vivas, S L Villegas-Pérez
• Journal: Journal of helminthology (J Helminthol) Vol. 89 Issue 5 Pg. 641-5 (Sep 2015) ISSN: 1475-2697 [Electronic] England
• PMID: 25226395 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Anthelmintics
• Benzimidazoles
• benzimidazole

Topics

• Animals
• Anthelmintics (administration & dosage)
• Benzimidazoles (administration & dosage)
• Drug Resistance
• Feces (parasitology)
• Female
• Goat Diseases (drug therapy, parasitology)
• Goats
• Haemonchiasis (drug therapy, parasitology, veterinary)
• Haemonchus (drug effects, genetics, isolation & purification, physiology)
• Larva (drug effects, genetics, physiology)