Heligmosomoides americanus is shown by molecular phylogenetic analysis of 3 nuclear (28S, ITS1, and ITS2) and 2 mitochondrial (cytochrome oxidase 1 and cytochrome b) loci to be a distinct species of heligmosomid nematode with a long-independent evolutionary history, and not a subspecies of Heligmosomoides polygyrus. Rather than being a recent arrival in North America, the species probably originated as a Beringian immigrant with the host vole Phenacomys, approximately 2 million years ago (MYA).

2015
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