Strongyloides stercoralis

• Common name?

  Threadworm
• Disease?

  Strongyloidiasis, Cochin-China Diarrhea
• Strongyloides stercoralis is known for its extra ordinary conditions such as?

  leading both a free living and parasitic existence
• principal host of S. Stercoralis?

  Human
• is there a parasite male?

  no
• the parasitic female being parthenogenetic is capable of self-fertilization without the participation of the male.
• There are two distinct stages of larva?

  Rhabditiform larva and Filariform larva
• This is a long, delicate larva with a long esophagus and with a forked or notched tail?

  Filariform larva
• This larva has a short buccal cavity, muscular elongated esophagus with a pyriform posterior bulb and a relatively conspicuous genital primordium. This is passed out in the feces.?

  Rhabditiform larva
• Parasitic female's paired uteri

  • Contain a single file of thin-shelled, transparent, partially embryonated eggs
  • Eggs are squarish resembling "Chinese lantern"
• These eggs are seldom seen in the feces
• 3 main life cycle stages?


  direct, indirect, and autoinfection
• • Direct cycle:
  • In the soil, eggs hatch into rhabditiform larvae (first larval stage).
  • Rhabditiform larvae molt (shed their skin) twice to become filariform larvae (infective stage).
  • Filariform larvae penetrate human skin, enter the bloodstream, travel to the lungs, and are coughed up, swallowed, and reach the small intestine where they mature into adults
• Indirect cycle:

  • Rhabditiform larvae develop into free-living adult males and females in the soil.
  • Free-living females lay eggs that develop into rhabditiform larvae.
  • These larvae can either repeat the free-living cycle or become filariform larvae under certain conditions.
  • Filariform larvae then infect humans as in the direct cycle.
• Autoinfection:

  • Rhabditiform larvae can mature rapidly into filariform larvae within the host's intestine.
  • They can penetrate the intestinal lining further down (ileum or colon), enter the bloodstream, travel through the heart and lungs, and return to the small intestine to mature.
  • Alternatively, filariform larvae may be passed in feces and re-infect the same person through the skin around the anus.
• Three stool samples, one per day for 3 days are recommended because S. stercoralis larvae may occur in “showers”