Strongyloides stercoralis

Strongyloides stercoralis	Contents	Rev 07/01/2025
Human threadworm	Classification	Biology and Ecology
	Morphology and Anatomy	Life Cycle
Return to Strongyloides Menu		Ecosystem Functions and Services
	Distribution	Management
Return to Strongyloididae Menu	Feeding	References
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Classification:

Class: Chromadorea; SubOrder: Rhabditia
Order: Rhabditida
Suborder: Tylenchina: Superfamily Strongyloidoidea
Family: Strongyloididae

Strongyloides stercoralis Stiles & Hassall, 1902

Morphology and Anatomy:

Strongyloides stercoralis Rhabditiform larva.

Males: free-living male adults are avout 0,9 mm long and 43um wide tail broad and slightly curved spicules paired	Female: parasitic females are long and slender, approximately 2.4 mm long and 37 um wide (hence the term threadworm). free-living females are approximately 1.1 mm long and 62 u wide, with a conical pointed tail parasitic and free-living females are amphidelphic parasitic females reproduce inside the host by parthenogenesis and generate both male and female larval progeny. free-licving females reprocude sexually and generate female larval progeny Rhabditiform Larvae: first-stage (L1), second-stage (L2) third-stage (L3) larvae, and fourth-stage (L4) larvae destined to become free-living adults consume bacteria and have a rhabditiform pharynx Ref: Castelleto et al., 2024
Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:

Distribution:

Workdwide distribution, human gastro-intestinal parasite

Feeding:

A skin-penetrating gastro-intestinal parasitic nematode that infects hundreds of millions of people worldwide.

Biology and Ecology:

Like other Strongyloides species, S. stercoralis can cycle through a free-living generation feeding on soil bacteria.

Cycles of autoinfection in healthy patients can result in chronic strongyloidiasis, which may be asymptomatic and can persist undetected for decades. In contrast, infections are often fatal in immuno-suppressed individuals or individuals with certain viral inefctions (Castelleto et al., 2024).

Like adults of Caenorhabditis elegans, the gonad of adults in the free-living generation is syncytial. Consequently, exogenous DNA can be introduced into free-living adults by intragonadal microinjection to generate transgenics and knockouts in their progeny. That makes the nematode very amenable as a genetic model system for the study of human-parasitic nematode biology (Castelleto et al., 2024).

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Life Cycle:

Like other Strongyloides species, S. stercoralis is capable of cycling through a a single free-living generation.

Parasitic adult females of S. stercoralis colonize the mucosal layer of the host small intestine. They produce eggs via mitotic parthenogenesis and deposit them in
the mucosal epithelium.
The eggs hatch into male and female post-parasitic first-stage larvae which migrate to the host intestinal lumen
Male larvae pass into the environment with the feces and develop into free-living adults.
Female post-parasitic larvae have three potential developmental routes: (i) pass into the environment with the feces and execute four molting cycles to become free-living adults which reproduce sexually to produce female larvae which develop to the L3 stage where development is arrested; (ii) develop directly to the L3 stage and on to free-living male and female adults which reproduce; (iii) remain in the host intestine and become autoinfective within the host.
Soil-dwelling L3s locate and penetrate a host, emerge from the developmentally-arrested state (activation), migrate to the lungs then through capillaries to the alveoli, are coughed up and swallowed by the host. Once they pass through the stomach into the intestine, the larvae develop into adult females (Castelleto et al., 2024)..

Ecophysiological Parameters:

For Ecophysiological Parameters for this species, click	If species level data are not available, click for genus level parameters