Soil-transmitted nematode (Strongyloides stercoralis) causing chronic GI/skin disease and life-threatening hyperinfection in immunocompromised hosts.
Also known as: Strongyloides stercoralis, strongyloidiasis, hyperinfection syndrome, threadworm
Overview
Infection by the soil-transmitted intestinal nematode Strongyloides stercoralis. Unique among helminths in its capacity for autoinfection, allowing infection to persist for decades and to cause overwhelming hyperinfection syndrome in immunocompromised hosts.
Epidemiology
Endemic to tropical and subtropical regions worldwide, with foci in the southeastern United States (Appalachia), Caribbean, sub-Saharan Africa, Latin America, and Southeast Asia. Estimates of global prevalence range from 30 to 600 million. US veterans of World War II Pacific theater, Vietnam, and Korean conflicts remain at risk decades later due to autoinfection.
🔒 Free preview limit reached
Keep reading — start your free trial
You've read your 2 free diagnosis previews. Create your free account to unlock the full Strongyloidiasis outline — plus all 514 diagnoses, 3,500+ board-style questions, flashcards, and an AI tutor. Your 7-day free trial includes everything, and there's no credit card required.
Residence in or travel to endemic tropical/subtropical regions
Walking barefoot on contaminated soil
Immunosuppression — particularly CORTICOSTEROIDS at any dose (most important reversible risk factor for hyperinfection)
HTLV-1 infection (major risk factor for hyperinfection)
Solid organ transplantation, hematologic malignancy
Older age (institutionalized adults)
Alcoholism, malnutrition
Pathophysiology
Filariform larvae penetrate skin → migrate via venous circulation to lungs → ascend trachea → swallowed → mature in small intestine. Female worms produce rhabditiform larvae that pass in stool OR mature within the host and reinvade the intestinal mucosa or perianal skin (autoinfection). Corticosteroids accelerate autoinfection by suppressing host eosinophil response and possibly directly stimulating the parasite, leading to hyperinfection — massive larval dissemination to lungs, CNS, and other organs, often with co-translocated gram-negative bacterial sepsis.
Cutaneous larva currens — pruritic, urticarial, serpiginous, rapidly migrating rash on buttocks, perineum, and lower trunk (pathognomonic, moves cm/hour)
Pulmonary: cough, wheezing, transient infiltrates (Loeffler syndrome) during initial migration
Hyperinfection: fever, severe abdominal pain, GI bleeding, ileus, ARDS, gram-negative bacteremia and meningitis
Disseminated infection in immunocompromised host with extraintestinal larvae in lungs, CNS, skin, liver
Signs / physical exam
Eosinophilia (often the only chronic finding; ABSENT in many hyperinfection cases — ominous)
Urticaria, larva currens pattern
Wheezing, crackles in pulmonary disease
Peritoneal signs in severe enteritis
Petechiae or 'thumbprint' periumbilical purpura in disseminated disease
Classic findings
Chronic peripheral eosinophilia in an immigrant or veteran from an endemic region. Larva currens (serpiginous, rapidly migrating urticarial rash). Hyperinfection in a patient started on corticosteroids without prior screening — sometimes with concurrent gram-negative bacteremia and meningitis.
Differential diagnosis
Other intestinal nematode infection (ascariasis, hookworm) — Eosinophilia, anemia in hookworm, GI/respiratory symptoms in ascariasis; ova on stool ovum-and-parasite exam
Loeffler syndrome (transient pulmonary infiltrates with eosinophilia) — Ascaris, hookworm, Strongyloides all cause migratory larval pneumonitis
Hyper-eosinophilic syndrome — Sustained eosinophilia without identifiable infection; rule out parasitic disease before steroids
Drug reaction with eosinophilia — Temporal medication exposure; recent antibiotic or anticonvulsant
Toxocara, Schistosoma, filariasis — Different geography and clinical syndrome; eosinophilia in many parasitic infections
Gram-negative sepsis / ARDS (in hyperinfection setting) — Often coexists with hyperinfection due to translocation of gut bacteria by migrating larvae
Diagnostic workup
Diagnostic criteria
Identification of larvae in stool, sputum, BAL, or tissue is definitive. In screening before immunosuppression, positive serology is sufficient indication for empirical treatment given the consequences of missed infection.
Labs
Stool ovum and parasite exam — LOW sensitivity even with multiple samples (rhabditiform larvae intermittently shed)
Stool agar plate culture and Baermann concentration — more sensitive
Strongyloides serology by ELISA — most sensitive screening test; preferred for screening before immunosuppression
Strongyloides PCR (where available)
CBC with differential (eosinophilia in chronic infection; may be absent in hyperinfection)
BMP, LFTs
Sputum or BAL for larvae in hyperinfection
Blood cultures (gram-negative bacteremia often accompanies hyperinfection)
HTLV-1 serology in high-risk patients
Imaging
Chest x-ray and CT: bilateral infiltrates or ARDS pattern in hyperinfection
Abdominal imaging if ileus or perforation suspected
MRI brain if neurologic findings (rare disseminated CNS larvae)
Diagnostic algorithm
flowchart TD
A[Filariform larvae<br/>penetrate skin] --> B[Venous migration to lungs<br/>Loeffler-like pneumonitis]
B --> C[Trachea -> swallowed -><br/>small bowel adult worms]
C --> D[Rhabditiform larvae in stool]
D --> E[Free-living cycle in soil]
C --> F[Autoinfection:<br/>larvae mature in host,<br/>reinvade bowel/perianal skin]
F --> G{Immunocompromise?<br/>Steroids? HTLV-1?}
G -->|No| H[Chronic infection<br/>eosinophilia, larva currens]
G -->|Yes| I[Hyperinfection /<br/>dissemination<br/>ARDS, GNR sepsis]
H --> J[Ivermectin 200 mcg/kg<br/>1-2 doses]
I --> K[Daily ivermectin until clear<br/>+ broad-spectrum antibiotics<br/>+ reduce immunosuppression]
Strongyloides lifecycle with autoinfection and the path from chronic infection to hyperinfection.
Treatment
First-line
Ivermectin 200 microg/kg PO daily for 1-2 days for uncomplicated chronic infection (some clinicians repeat dose at 2 weeks)
Hyperinfection or disseminated disease: ivermectin 200 microg/kg/day until stool and sputum are negative for at least 2 weeks (typically 1-2+ weeks of daily dosing); subcutaneous ivermectin (veterinary product, off-label) for patients with malabsorption or ileus, in consultation with infectious diseases
Add empirical broad-spectrum antibacterial coverage for gram-negative enteric organisms in hyperinfection (gut translocation)
Reduce or discontinue corticosteroids and other immunosuppressants when possible
Pre-immunosuppression screening with serology in patients from endemic regions and treatment of positive results before steroid therapy or transplant
Second-line / adjunct
Albendazole 400 mg PO BID for 7 days — less effective than ivermectin; alternative only when ivermectin unavailable or contraindicated
Combination ivermectin + albendazole has been used in refractory disease
Repeat testing 3-6 months post-treatment to document cure (serology may decline slowly)
Complications
Hyperinfection syndrome with massive autoinfection and end-organ damage
Disseminated strongyloidiasis to lungs, CNS, liver, skin
Gram-negative bacteremia and meningitis from larval bowel translocation
ARDS, shock, multiorgan failure
Death rates >50% in disseminated disease despite treatment
Chronic malabsorption and protein-losing enteropathy
PANCE pearls
Screen with Strongyloides serology in any patient from an endemic area BEFORE starting corticosteroids, biologics, transplant, or chemotherapy.
Larva currens — rapidly migrating serpiginous rash — is highly specific for Strongyloides.
Eosinophilia is the chronic-infection marker but is OFTEN ABSENT in hyperinfection; do not let normal eosinophils reassure you.
Co-existing HTLV-1 infection markedly increases the risk of hyperinfection and reduces ivermectin efficacy.
Hyperinfection patients often present with concurrent gram-negative bacteremia or meningitis — empirically cover gut flora.
References
CDC — CDC Parasites — Strongyloides: epidemiology, diagnosis, and treatment
WHO — WHO Guideline on control and elimination of human schistosomiasis and soil-transmitted helminthiases (includes Strongyloides considerations)
IDSA / ASTMH — Practice guidelines for the management of soil-transmitted helminth infections
Practice Infectious Disease questions on FirstPassPA
Turn this outline into retention. 3,500+ board-style questions with an AI tutor that explains every answer — free to start, no card required.
Educational use only. This outline is a study aid for PA students and is not medical advice or a substitute for clinical judgment. FirstPassPA is an independent study tool and is not affiliated with, endorsed by, or sponsored by NCCPA. PANCE® and PANRE® are registered trademarks of the National Commission on Certification of Physician Assistants.