Worms passed in stool may be submitted to the microbiology laboratory for examination. Ascaris and Anisakid worms (A and B) are human pathogens; Lumbricus and horsehair worms (C and D) are not human pathogens.
(A) Adult Ascaris worms are 15 to 35 cm in length with a smooth surface and continuous color throughout.
(B) Anisakid worms (Anisakis or Pseudoterranova) L3 larva are 1 to 2 cm in length. They may be observed in stool; more commonly, they are observed on upper endoscopy. They may also be found in vomitus or in cooked fish. Anisakid worms appear translucent to light brown.
(C) Lumbricus worms are earthworms that may migrate into sewage systems and be found in toilet water; they are not human pathogens. The worms have ridges all along their body as well as a distinctive clitellum (smooth, ridgeless structure); variations in color may be observed.
(D) Horsehair worms live inside insects including crickets and cockroaches; they may be found in toilets after disposal of dead insects but are not human pathogens. The worms are about 10 cm and very thin; they are light to dark brown.
