Strongyloidiasis (Threadworm)

A parasitic infection caused by the intestinal nematode Strongyloides stercoralis.

Aetiology

Causative Organisms

Strongyloides stercoralis
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Pathophysiology

The infection occurs via the fecal–oral route.

Life Cycle Stages

  1. Filariform larvae in soil penetrate human skin
  1. Enter bloodstream → migrate to lungs
  1. Ascend bronchial tree → swallowed
  1. Mature into adult female worms in small intestine
  1. Eggs hatch into rhabditiform larvae in intestine
  1. Larvae are:
      • Excreted in stool, or
      • Cause autoinfection by penetrating intestinal mucosa or perianal skin
Autoinfection explains chronic infection and hyperinfection syndrome.
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Pathogenesis

Stage
Pathology
Skin penetration
Local inflammation
Pulmonary migration
Eosinophilic pneumonitis
Intestinal phase
Mucosal inflammation
Autoinfection
Continuous parasite cycle
Hyperinfection
Massive dissemination in immunocompromised patients
Severe disseminated disease is common in patients with:
  • Corticosteroid therapy
  • Organ transplantation
  • Hematologic malignancy
  • Human Immunodeficiency Virus Infection (less common but possible)

Clinical Presentation

Cutaneous Manifestations

Feature
Description
Pruritic rash
At entry site
Larva currens
Rapidly migrating serpiginous rash
Urticaria
Hypersensitivity reaction
Larva Currens
Larva Currens

Pulmonary Manifestations

Symptom
Mechanism
Cough
Larval migration
Wheezing
Airway irritation
Dyspnea
Eosinophilic pneumonitis
 

Gastrointestinal Manifestations

Symptom
Description
Abdominal pain
Epigastric discomfort
Diarrhea
Intermittent
Nausea and vomiting
GI irritation
Malabsorption
Chronic infection

Hyperinfection Syndrome

Occurs mainly in immunocompromised patients.
System
Manifestation
GI
Severe diarrhea
Pulmonary
Respiratory failure
Sepsis
Gram-negative bacteremia
CNS
Meningitis

Investigations

Test
Findings
Stool microscopy
Rhabditiform larvae
Stool concentration techniques
Increased detection
Agar plate culture
Larval tracks
Serology (ELISA)
Detect antibodies
CBC
Eosinophilia
Sputum exam
Larvae in hyperinfection
Important point:
Eggs are rarely seen in stool because they hatch in the intestine.
 

Management

First-Line

Drug
Dose
Ivermectin
200 µg/kg/day for 1-2 days
Albendazole
400 mg 2x1 for 7 days