Epidemiology and Etiology
- Worldwide prevalence: 100 million cases currently
- Most common in tropical and warm temperate regions, with ¾ of cases in Southeast Asia, Africa, and Western Pacific countries
Strongyloidiasis is caused by a parasitic infection by the roundworm (nematode) Strongyloides stercoralis. Roundworms are nonsegmented worms that can infect the GI tract, blood, or skin.
- The ability to “auto-infect” its host leads to chronic cases.
- Adult males: 0.9 mm (0.04 in) long, can be distinguished from females by size and presence of spicules (needle-like mating structure)
- Adult females: 2.0–2.5 mm (0.08–0.10 in) long
Life cycle of S. stercoralis
- Filariform larvae in contaminated soil penetrate human skin.
- Larvae migrate through bloodstream and lymphatics to lungs.
- In lung parenchyma, larvae penetrate alveoli and migrate up trachea and larynx.
- Larvae are then swallowed by the host.
- Swallowed larvae enter GI tract.
- Larvae mature within mucosa of small intestine.
- Adult larvae produce eggs, which yield noninfectious, rhabditiform larvae that migrate to intestinal lumen and are excreted in feces.
- Autoinfection can occur in hosts with compromised immune systems:
- Noninfectious, rhabditiform larvae mature into infectious, filariform larvae within the intestine.
- Filariform larvae penetrate intestinal mucosa or perianal skin to migrate through bloodstream and lymphatics to restart infectious cycle.
- Humans (most common)
- Cats and dogs
- Most common: larvae found in contaminated sand or soil penetrate skin
- Fecal-oral transmission (less common)
Host risk factors
- Walking barefoot on contaminated soil
- Contact with human waste or sewage
- Occupations that increase contact with contaminated soil (farming and coal mining)
Phases of strongyloidiasis infection
Strongyloidiasis can cause both acute and chronic infection. Symptoms correlate with the migration of the larvae from the skin, lung, and intestine.
- Cutaneous phase: secondary to penetration of larvae into skin
- Maculopapular rash with serpiginous lesions (larva currens)
- Pulmonary phase: secondary to migration of larvae through bronchial tree and alveoli
- 1 week after skin penetration
- Löffler syndrome (pulmonary eosinophilia): transient respiratory disorder characterized by accumulation of eosinophils in lungs due to parasitic infection
- Dry cough
- Throat irritation
- GI phase: secondary to adult larvae within mucosa of small intestine
- 3–4 weeks after skin penetration
- Abdominal pain
- Diarrhea or constipation
- Hyperinfection syndrome: occurs due to acceleration of Strongyloides life cycle
- Excessive worm burden within traditional reproductive route (skin, lungs, and intestines)
- Occurs most often in immunosuppressed patients
- Disseminated strongyloidiasis: due to widespread dissemination of larvae outside traditional reproductive route, often involving liver, brain, heart, and urinary tract
- Altered mental status
- Focal seizures
- Chest pain
- Dyspnea (can progress to acute respiratory distress syndrome)
- Abdominal pain
- GI inflammation and hemorrhage
- Small bowel obstruction
Diagnosis and Management
Diagnosis requires a high clinical suspicion test, based on symptoms.
- Common finding in chronic infections
- Nonspecific finding
- Skin biopsy: may provide microscopic identification of mobile rhabditiform larvae
- Serologic studies
- Indirect immunofluorescence microscopy
- Stool studies: identify parasite in feces
- Endoscopy not routinely performed
- Anthelmintic medication:
- 1st line: ivermectin
- For complicated infections in immunosuppressed individuals, albendazole may be added.
- Treatment may need to be repeated for persistent infections.
- Use of footwear when walking outdoors, especially on soil or sand in endemic regions
- Proper sewage disposal and fecal management
- Pulmonary phase:
- Tuberculosis: pulmonary bacterial infection caused by Mycobacterium tuberculosis, which may present asymptomatically or with fever, weight loss, night sweats, hemoptysis, and productive cough.
- Ascariasis: infection caused by a parasitic roundworm, Ascaris lumbricoides. May present asymptomatically or with abdominal discomfort, bowel obstruction, and Löffler syndrome.
- GI phase:
- Crohn’s disease: inflammatory bowel disease characterized by inflammation of GI tract, presenting with signs of malabsorption, abdominal pain, and non-bloody, chronic diarrhea.
- Peptic ulcer disease: presence of 1 or more ulcerative lesions in stomach or lining of duodenum, presenting with dyspepsia. May progress with signs of GI bleeding.
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