A population genetic analysis of the nematode <i>Strongyloides stercoralis</i> in Asia shows that human infection is not a zoonosis from dogs.

Abstract

Gut nematode worms are important parasites of people and other animals. The parasitic nematode <i>Strongyloides stercoralis</i> infects an estimated 600 million people worldwide and is one of the soil-transmitted helminthiases, a WHO-defined neglected tropical disease. It has long been suggested that human <i>S. stercoralis</i> infection may be a zoonosis from dogs. We investigated this by whole genome sequence analysis of <i>S. stercoralis</i> from sympatric human and dog populations in Asia. We find that human- and dog-derived <i>S. stercoralis</i> have genetically distinct nuclear genomes, but we also find evidence of rare cross-infection. Analysis of the <i>S. stercoralis</i> mitochondrial genome reveals evidence of historical introgression between human- and dog-derived parasites. Based on these data, we suggest that <i>S. stercoralis</i> was originally a parasite of canids, that began to infect humans when people domesticated dogs, since when human- and dog-derived parasites have differentiated, but have not become separate species.