Strongyloides stercoralis		Contents		Rev 09/07/2025
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
		Go to Nemaplex Main Menu		Go to Dictionary of Terminology

Classification:

Synonyms:

Anguillula stercoralis Bavay, 1876

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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 reproducee 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:

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Distribution:

Worldwide distribution, human gastro-intestinal parasite, causing strongyloidiasis.As many as 370 million people may be infected worldwide (Schar et al., 2013)..

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Feeding:

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

The adult parasitic stage lives in tunnels in the mucosa of the small intestine.

Besides humans, S. stercoralis has also been reported in domestic dogs and cats. However, the spexcies in dogs is usually S. canis

Non-human primates are commonly infected with S. fuelleborni and S. cebus, although S. stercoralis has been reported in captive primates

Symptoms of infection include itching at site of infection, pneumonia-like  symptoms if lung-infection occurs, and intestinal tissue damage, sepsisa nd even intestinal obstruction (Roberts and Janovy, 2009).

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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 free-living generation with an alternation of free-living and parasitic cycles.

• 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:

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Ecosystem Functions and Services:

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Management:

Strongyloides stercoralis infection is usually associated with fecal contamination of soil or water. Hence, infections in developed economies are quite rare. In developing countries, it is less prevalent in urban areas than in rural areas (where sanitation standards are poor). Strogyloides stercoralis infections are most common in tropical and subtropical climates.

Improved sanitation

Anthelmithics including ivermectin

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References:

Castelleto, M.L., Skimon, D., Patel, R. Schroeder, N.E., Hallem, E.A, 2024. Introduction to Strongyloides stercoralis anatomy. J. Nematology 56: DOI: 10.2478/jofnem-2024-0019

Roberts, L.S.; Janovy, J. Jr. 2009. Foundations of Parasitology, Eighth Edition. United States: McGraw-Hill

Schar, F; Trostdorf, U; Giardina, F; Khieu, V; Muth, S; Marti, H; Vounatsou, P; Odermatt, P. 2013. Strongyloides stercoralis: Global Distribution and Risk Factors. PLOS Neglected Tropical Diseases. 7 (7): e2288. doi: 10.1371.journal.pntd.0002288

Wikipedia: Accessed September, 2025

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Copyright © 1999 by Howard Ferris.
Revised: September 07, 2025.