Strongyloidiasis: Really a Zoonosis?

More than 600 million people are estimated to be infected with the nematode Strongyloides stercoralis, which is often overlooked during routine parasitological diagnostics. Some of the young worms mature to infective larvae within the host, enabling this parasite to establish long-lived, self-sustaining infections. While most of these infections are mild, they can self-enhance, resulting in complicated strongyloidisas, which if not treated in time, is normally lethal. While it is undisputed that dogs are susceptible to experimental infection with human-derived S. stercoralis, it has long been debated if Strongyloides sp. naturally found in dogs are human infective S. stercoralis or belong to a different species, S. canis. Based on recent studies, I argue that dogs naturally carry S. stercoralis, in addition to at least one other species, for which we have no indication that it infects people. I argue that for all practical purposes of S. stercoralis treatment and prevention, dogs should be seriously considered as possible sources for human S. stercoralis. However, from a rigorous scientific point of view, we must admit that currently we have no idea about the relative importance of zoonotic transmission compared with human to human transmission