Definition: Strongyloidiasis is an infection with Strongyloides stercoralis, a round worm occurring widely in tropical and subtropical areas.
The genus Strongyloides is classified in the order Rhabditida, and most members are soil-dwelling microbiverous nematodes. Fifty-two species of Strongyloides exist, but most do not infect humans. S. stercoralis is the most common pathogen for humans.
The adult male worm is passed in the stool after fertilizing the female worm - it is not a tissue parasite. The adult female worm is very small and almost transparent. It measures approximately 2.2-2.5 mm in length with a diameter of 50 µm; it lives in tunnels between the enterocytes in the human small bowel.