Molecular evidence of hybridization between pig and human Ascaris indicates an interbred species complex infecting humans

Abstract

Human ascariasis is a major neglected tropical disease caused by the nematodeAscaris lumbricoides. We report a 296 megabase (Mb) reference-quality genome comprised of 17,902 protein-coding genes derived from a single, representativeAscarisworm. An additional 68 worms were collected from 60 human hosts in Kenyan villages where pig husbandry is rare. Notably, the majority of these worms (63/68) possessed mitochondrial genomes that clustered closer to the pig parasiteAscaris suumthan toA. lumbricoides. Comparative phylogenomic analyses identified over 11 million nuclear-encoded SNPs but just two distinct genetic types that had recombined across the genomes analyzed. The nuclear genomes had extensive heterozygosity, and all samples existed as genetic mosaics with eitherA. suum-like orA. lumbricoides-like inheritance patterns supporting a highly interbredAscarisspecies genetic complex. As no barriers appear to exist for anthroponotic transmission of these ‘hybrid’ worms, a one-health approach to control the spread of human ascariasis will be necessary.