title: Phenotypic and genotypic analysis of benzimidazole resistance in the ovine parasite Nematodirus battus.
abstract: Benzimidazole resistance is common amongst many ovine trichostrongylid nematodes species globally. Although anthelmintics have been used for over half a century in some areas of the world for the control of Nematodirus battus, resistance has never been detected. Veterinary investigations conducted in 2010 demonstrated reduced efficacy in a flock that had been treated previously with fenbendazole (FBZ), suggesting probable resistance in N. battus. Infective larvae (L3; designated MNba2) were generated from the original material to conduct a controlled efficacy test (CET). Faecal egg counts showed an average of 37% reduction in the FBZ treated group 7 days post treatment compared to the untreated lambs. Average worm burden results showed no reduction after FBZ treatment compared to the untreated group (3850 and 3850 worms respectively). A molecular assay to assess the frequency of the commonly associated single nucleotide polymorphisms (SNP) in the β-tubulin isotype 1 gene, F200Y and E198A, was developed. Larval genotypes were predominantly homozygous resistant at codon 200 SNP, ranging from 56%-83% and remained stable at 70% for adult worm populations taken from treated and control lambs in the CET. Only susceptible genotypes were found at codon 198. The allele frequency for F200Y ranged between 80-83% in adult worms taken from the CET from treated and control lambs. The results confirmed initial findings and demonstrated the first report of FBZ resistance in N. battus whilst providing evidence that the P200 point mutation in the β-tubulin isotype 1 gene is a potential mechanism of resistance in the species.
authors.affiliation: Moredun Research Institute, Pentlands Science Park, Bush Loan, Penicuik, EH26 0PZ, UK. alison.morrison@moredun.ac.uk.
authors.forename: Alison A
authors.initials: AA
authors.lastname: Morrison
authors.affiliation: Animal Health and Veterinary Laboratories Agency, Camarthen, Job's Well Road, Johnstown, Camarthen, SE31 3EZ, UK. Sian.Mitchell@ahvla.gsi.gov.uk.
authors.forename: Sian
authors.initials: S
authors.lastname: Mitchell
authors.affiliation: Animal Health and Veterinary Laboratories Agency, Penrith, Merrythought, Calthwaite, Penrith, Cumbria, CA11 9RR, UK. Rebecca.Mearns@ahvla.gsi.gov.uk.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Mearns
authors.affiliation: Care of Westmorland Veterinary Group, Riverside Business Park, Natland Road, Kendal, LA9 7SX, UK. iain@lakesvet.demon.co.uk.
authors.forename: Iain
authors.initials: I
authors.lastname: Richards
authors.affiliation: Moredun Research Institute, Pentlands Science Park, Bush Loan, Penicuik, EH26 0PZ, UK. jacqui.matthews@moredun.ac.uk.
authors.forename: Jacqui B
authors.initials: JB
authors.lastname: Matthews
authors.affiliation: Moredun Research Institute, Pentlands Science Park, Bush Loan, Penicuik, EH26 0PZ, UK. dave.bartley@moredun.ac.uk.
authors.forename: David J
authors.initials: DJ
authors.lastname: Bartley
mesh_terms: D000818:Animals; D000871:Anthelmintics / Q000494:pharmacology; D001562:Benzimidazoles / Q000494:pharmacology*; D004351:Drug Resistance / Q000235:genetics*; D005243:Feces / Q000469:parasitology; D005838:Genotype; D015801:Helminth Proteins / Q000235:genetics* / Q000378:metabolism; D007814:Larva / Q000187:drug effects; D057808:Nematodirus / Q000187:drug effects* / Q000235:genetics*; D010270:Parasite Egg Count / Q000662:veterinary*; D016133:Polymerase Chain Reaction / Q000662:veterinary; D020641:Polymorphism, Single Nucleotide; D012756:Sheep; D012757:Sheep Diseases / Q000469:parasitology / Q000517:prevention & control; D017206:Strongylida Infections / Q000469:parasitology / Q000517:prevention & control / Q000662:veterinary; D014404:Tubulin / Q000235:genetics* / Q000378:metabolism
chemical_list: D000871:Anthelmintics; D001562:Benzimidazoles; D015801:Helminth Proteins; D014404:Tubulin; C031000:benzimidazole