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[Strongyloides stercoralis]

Infective, third-stage filariform larvae (L3) of Strongyloides stercoralis are up to 600 µm long.  The tail is notched and the esophagus to intestine ratio is 1:1.  Infective L3 larvae are found in soil and invade the human host by direct penetration of the skin.  They may be found in respiratory specimens during cases of autoinfection.

A	B

A: Filariform (L3) larva of S. stercoralis in an unstained wet mount.
B: Filariform (L3) larva of S. stercoralis in a sputum specimen, stained with Giemsa.  Image taken at 200x magnification.

C

C:  Higher magnification (1000x oil) of the worm in Figure B.  Notice the notched tail.