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[Strongyloides stercoralis]

Adults of Strongyloides stercoralis may be found in the human host or soil.  In the human host there are no parasitic males, and parasitic females are long, slender and measure 2.0-3.0 mm in length.  In the environment, rhabditoid larvae may develop into infective filariform (L3) larvae (direct cycle) or free-living adults that contain both males and females (indirect cycle).  Free-living adult males measure up to 750 µm long; free-living females measure up to 1.0 mm long.

A	B

A: Free-living adult male S. stercoralis. Notice the presence of the spicule (red arrow).
B: Free living adult male S. stercoralis, showing a spicule (red arrow).  A smaller, rhabditiform larva lies adjacent to the adult male.

C	D

C: Adult free-living female S. stercoralis alongside a smaller rhabditoid larva.  Notice the developing eggs in the adult female.
D: Adult free-living female S. stercoralis.  Notice the row of eggs within the female’s body.