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Parasite life cycles - strongyloides stercoralis

4 important questions on Parasite life cycles - strongyloides stercoralis

Summary of free-living life cycle

Rhabditiform larvae are passed in the stool of definitive host.
These develop into infective filariform L3 larvae (direct development)

OR they develop into free-living adult males and females, that mate and produce eggs. From those eggs rhabditiform larvae hatch and become infective filariform larvae.

Summary of parasitic cycle

Filariform larvae in contaminated soil penetrate human skin and migrate to the small intestine
In the small intestine, the larvae become adult female worms
The female worms live in the small intestine and produce eggs via parthenogenesis, which yields rhabditiform larvae
The rhabditiform larvae can either be passed in the stool of cause autoinfection

How does autoinfection work

Rhabditiform larvae in the gut become infective filariform larvae that can penetrate the intestinal mucosa or the perianal skin

How do the larvae migrate to the intestine?

L3 larvae migrate via bloodstream and lymphatics to the lungs, where they are coughed up and swallowed.
L3 larvae may also migrate to the intestines via alternate routes