[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Nematodes](https://durgical.com/en/microbiology/groups/nematodes/) › Strongyloides stercoralis

[Microbiology](https://durgical.com/en/microbiology/) · [Nematodes](https://durgical.com/en/microbiology/groups/nematodes/)

# Strongyloides stercoralis

- Parasite
- Exam priority: high

A worm that reinfects its host and can live in the body for decades. Under steroids it multiplies out of control and can cause fatal infection.

Updated 2026-11-01

Also called: threadworm (Strongyloides)

## Key points

- Larvae (not eggs) in stool.
- Autoinfection: persists for decades after leaving the endemic area.
- Steroids and HTLV-1 → hyperinfection with mortality near 90%.
- Unexplained gram-negative sepsis or meningitis: think Strongyloides.
- Ivermectin is the drug of choice; mass-campaign benzimidazoles do not control it well.

## At a glance

**Shape**
Threadlike parasitic female embedded in the small-bowel mucosa

**Family**
Strongyloididae

**Type**
Intestinal nematode with a free-living soil cycle

**Size**
Parasitic female about 2–3 mm

## Morphology

- Stool shows rhabditiform larvae, not eggs.
- Rhabditiform larva with a short buccal canal and a prominent genital primordium (hookworm larvae have a long buccal canal).
- Filariform larva with a notched tail.

## Transmission

- Skin penetration by filariform larvae from contaminated soil.
- Internal or perianal autoinfection, which keeps the infection going for decades.
- Rarely, transplant of an organ from an infected donor.

**Reservoir:** Humans; Warm moist soil (free-living cycle)

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Life cycle

- The filariform larva in soil penetrates skin and migrates to the small bowel.
- Females embed in the mucosa and reproduce without males (parthenogenesis).
- Eggs hatch in the mucosa: rhabditiform larvae, not eggs, leave in stool.
- In soil the larvae become filariform or form free-living adults that reproduce.
- Autoinfection: larvae turning filariform in the gut reinvade the bowel wall or perianal skin.
- With steroids or HTLV-1, autoinfection speeds up: hyperinfection and dissemination.

## Virulence factors

- Autoinfection allows decades-long infection, even far from endemic areas.
- In hyperinfection, millions of larvae cross the bowel wall carrying enteric bacteria.
- This explains gram-negative bacteraemia and meningitis in disseminated disease.
- Larva currens: a fast-moving serpiginous rash on the buttocks, perineum and thighs.

## Diseases it causes

- Chronic strongyloidiasis and hyperinfection syndrome or disseminated disease [Strongyloidiasis →](https://durgical.com/en/conditions/strongyloidiasis/)
- Gram-negative sepsis in hyperinfection [Sepsis and septic shock →](https://durgical.com/en/conditions/sepsis-and-septic-shock/)

## Clinical picture

- Many chronic carriers are asymptomatic or have mild GI symptoms.
- Recurrent larva currens and mild eosinophilia in chronic infection.
- Hyperinfection: lung infiltrates, ileus, GI bleeding, gram-negative sepsis and meningitis.
- Eosinophilia is often absent in hyperinfection; its absence does not rule it out.

## Diagnosis

- Larvae in serial stool samples: direct microscopy is insensitive and several samples are needed.
- Agar plate culture (Koga method), the most sensitive stool method; Baermann also used.
- Duodenal aspirate or string test; larvae in bronchoalveolar lavage in hyperinfection.
- Serology (EIA) for screening and follow-up; PCR in reference centres.

## Treatment

Ivermectin is the drug of choice; albendazole is an alternative. People from endemic areas are screened (and treated if positive) before steroids, chemotherapy or transplant, as are those with HTLV-1.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

- [Ivermectin](https://durgical.com/en/pharmacology/ivermectin/)
- [Albendazole](https://durgical.com/en/pharmacology/albendazole/)

## Prevention

- Shoes and basic sanitation.
- Screening before steroids or other immunosuppressants in exposed people.
- Consider Strongyloides in anyone with HTLV-1.
- Screening of organ donors from endemic areas.

## In Colombia

Present in warm, humid parts of the country but underdiagnosed, because routine stool exams rarely detect the larvae. Agar plate culture and serology improve detection.

## Memory aid

The guest who never leaves: Strongyloides reinfects itself, and steroids open the door to the bloodstream, bacteria and all.

## Test yourself

Think of the answer, then tap the question to see it.

## What is looked for in stool to diagnose Strongyloides?

Rhabditiform larvae, because the eggs hatch in the mucosa before leaving the body.

## Which drug class most often triggers Strongyloides hyperinfection?

Corticosteroids, which accelerate autoinfection.

## Why does hyperinfection come with gram-negative sepsis?

Larvae cross the bowel wall en masse and carry enteric bacteria into the blood.

## What is the most sensitive stool method for Strongyloides?

Agar plate culture (Koga method).

## Which virus is linked to severe strongyloidiasis?

HTLV-1.

[Add to my cards (5)](https://durgical.app/estudiar/?add=/en/microbiology/strongyloides-stercoralis/)

## Related

- [Necator americanus / Ancylostoma duodenale](https://durgical.com/en/microbiology/necator-americanus-ancylostoma-duodenale/)
- [Ancylostoma braziliense / Ancylostoma caninum](https://durgical.com/en/microbiology/ancylostoma-braziliense-ancylostoma-caninum/)

## Related conditions

- [Strongyloidiasis](https://durgical.com/en/conditions/strongyloidiasis/)
- [Sepsis and septic shock](https://durgical.com/en/conditions/sepsis-and-septic-shock/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

[← Back to the group: Nematodes](https://durgical.com/en/microbiology/groups/nematodes/)

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [CDC - DPDx - Strongyloidiasis](https://www.cdc.gov/dpdx/strongyloidiasis/index.html) (CDC, 2019); [Clinical Overview of Strongyloides | Strongyloides | CDC](https://www.cdc.gov/strongyloides/hcp/clinical-overview/index.html) (CDC, 2026); [Clinical Care of Strongyloides | Strongyloides | CDC](https://www.cdc.gov/strongyloides/hcp/clinical-care/index.html) (CDC, 2024); [Strongyloidiasis: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000630.htm) (MedlinePlus (NLM), 2024).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/microbiology/strongyloides-stercoralis/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/strongyloides-stercoralis/