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

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 contort its. We crossed a multi-drug resistant field isolate of H. contortus with a well-characterized laboratory strain susceptible to 4 drug classes. The F-2 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 F-2 worms were analysed using amplicon length polymorphisms (ALPs). We looked for field isolate alleles over- or under-represented in F-2 populations compared to the unselected F-2 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.