The Strongyloides stercoralis nervous system.

The skin-penetrating, human-parasitic nematode Strongyloides stercoralis infects over 600 million people worldwide, causing extensive morbidity and socioeconomic burden. Outside the host body, these nematodes usually live in moist soil as infective third-stage larvae (iL3s), a life stage that is considered to be evolutionarily homologous to the dauer stage of free-living nematodes such as Caenorhabditis elegans. S. stercoralis iL3s navigate their local environment and seek out hosts using sensory cues such as heat, host-emitted odorants, and carbon dioxide. Once host contact is made, iL3s actively explore the surface of the skin before penetrating the tissue and entering the body. Inside the body, iL3s navigate to the small intestine, where they live and reproduce as parasitic adults. The nervous system of S. stercoralis orchestrates the various sensory and motor behaviors that are necessary for successful passage through the parasite life cycle. Here, we describe our current understanding of the structure of the nervous system of the S. stercoralis iL3 stage. We highlight the neurons that drive behaviors such as dispersal, host seeking, and skin penetration. Additionally, we identify differences between the nervous systems of S. stercoralis iL3s and C. elegans dauers; these adaptations likely contribute to the differences in behavior and lifestyle between these two species of nematodes.