The use of DNA markers to map anthelmintic resistance loci in an intraspecific cross ofHaemonchus contortus

Abstract

The use of DNA markers to track the development of anthelmintic resistance in parasites of livestock would allow informed choices for the management of this important problem. We describe a genetic mapping approach for the discovery of DNA markers for anthelmintic resistance in Haemonchus contortus. We crossed a multi-drug resistant field isolate of H. contortus with a well-characterized laboratory strain susceptible to 4 drug classes. The F2 were separately selected with 5 anthelmintics from 4 drug classes, producing drug-resistant populations carrying gene variants derived from both the field isolate and the laboratory strain. Individual F2 worms were analysed using amplicon length polymorphisms (ALPs). We looked for field isolate alleles over- or under-represented in F2 populations compared to the unselected F2 and/or the laboratory strain. The data we obtained suggest that marker association can be used to link neutral markers with resistance, but also that more markers and perhaps more inbred laboratory strains would make the procedure more likely to succeed.

Introgression of Ivermectin Resistance Genes into a Susceptible Haemonchus contortus Strain by Multiple Backcrossing

“…Previous genetic crossing experiments have been performed to assess the level of dominance of resistance genes and test for evidence of linkage of a P-glycoprotein with the ivermectin resistance phenotype [9], [11], [43]–[45]. More recently, a genetic mapping approach was undertaken in which resistant F 2 were selected and AFLP used to look for markers associated with resistance [8]. This was a potentially powerful approach although, in that case, the ability to analyze the F 2 progeny was limited by the lack of genetic differentiation of the parental strains used.…”

“…It is also one of the most amenable parasitic nematodes to experimental manipulation which, together with recent progress in sequencing its genome makes it a potentially powerful model system to study drug resistance in the strongylid nematode group [7]. In addition, genetic crossing is technically possible in this parasite and has potentially powerful applications in the study of anthelmintic resistance providing we can develop the necessary techniques and resources [8]–[11].…”

Recent advances in candidate-gene and whole-genome approaches to the discovery of anthelmintic resistance markers and the description of drug/receptor interactions

“…In more recent years, the continued absence of useful molecular markers for ivermectin and other ML resistances in field populations of parasites (as described in the previous section) has led to a re-examination of the likely genetic mechanisms of resistance. A study of F2 populations of H. contortus crosses between a field resistant isolate (Wallangra2003) and a laboratory cultured susceptible parent (McMaster 1931), indicated that the level of IVM resistance displayed by the F2 (and derived from Wallangra2003) could not be explained using a single gene model ( Hunt et al, 2010 ). This has recently been supported by two serial backcross experiments between the susceptible strain MHco3 (ISE) and two ivermectin resistant strains MHco10 (ISE) and MHco4 (WRS) in which the proportion of the phenotypically resistant individuals present after the fourth backcross was consistent with a multi-genic basis of resistance ( Redman et al, 2012 ).…”

Population genomic and evolutionary modelling analyses reveal a single major QTL for ivermectin drug resistance in the pathogenic nematode, Haemonchus contortus

“…Genome-wide and genetic mapping approaches are emerging for H. contortus due to progress in genetic crossing methodologies [21,[35][36][37][38][39][40] and an increasing complement of genomic resources [19][20][21] . Two serial backcrosses have previously been undertaken between the susceptible isolate MHco3(ISE) and two geographically independent ivermectin resistant isolates, MHco4(WRS) and MHco10(CAVR) [39] ( Fig 1 A,B ).…”