Abstract
Helminth infections cause an enormous disease burden in humans, livestock and companion animals. Helminth control is heavily dependent on the regular administration of anthelmintic drugs. Resistance to these drugs is widespread in many livestock systems, and there is concern that mass drug administration programs to control human helminths may be selecting for resistance. Here, we build on two previous genetic crosses between ivermectin resistant and sensitive isolates of the parasitic nematode Haemonchus contortus, an economically important gastrointestinal parasite of small ruminants that is a model for anthelmintic research. By combining genetic mapping and whole genome sequencing with novel analyses, we identify the first single genomic locus conclusively associated with ivermectin resistance in a parasitic nematode. This locus is common between two geographically and genetically divergent strains and does not include leading candidate genes. This work represents the first example of a major anthelmintic resistance locus being identified by genetic mapping in a parasitic nematode and represents the most comprehensive genetic analysis of this trait in a parasitic nematode to date.