Phenotypic and genotypic analysis of benzimidazole resistance in the ovine parasite Nematodirus battus

Alison A Morrison,Sian Mitchell,Iain Richards,Rebecca Mearns,Jacqui B Matthews,David J Bartley

doi:10.1186/preaccept-1940024174137375

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.

Highlights

There are several species of Nematodirus that cause disease and production losses in young lambs, most of the losses in the UK are caused by Nematodirus battus [1,2,3]
Lambs can present with severe scouring and other clinical signs before there are well established levels of adult worms and, eggs appearing in faeces
Parasite isolate Faecal material was collected from lambs following an on-farm FBZ faecal egg count reduction test (FECRT) which indicated the presence of benzimidazole resistance [27]

Summary

Introduction

There are several species of Nematodirus that cause disease and production losses in young lambs, most of the losses in the UK are caused by Nematodirus battus [1,2,3]. Nematodirosis is a disease that is normally seen in young lambs, the signs of infection are often acute and, if left unchecked, can result in a high (typically 5-20%) mortality rate [3]. All classes have licensed efficacy against N. battus, activity against certain life stages ( immatures) can vary by Several genetic mechanisms have been associated with BZ resistance in parasitic nematodes of sheep; for example, loss of isotype 2 of the β-tubulin gene and single nucleotide polymorphism (SNP) within isotype 1 of the β-tubulin gene [19,20]. SNPs in the β-tubulin gene are Morrison et al Veterinary Research (2014) 45:116

Methods

Results

Conclusion