Strongyloides stercoralis

• Commonly known as threadworm

Background

Life Cycle

• Eggs are released in the small intestine, then hatch to release rhabditiform larvae
• The rhabditiform larvae are excreted, where they molt and develop into infective filariform larvae or into free-living adult males and females
  • Free-living adults mate and produce rhabditiform larvae
  • Rhabditiform larvae can also develop into filariform larvae within the large bowel, then perforate through the bowel or rectal mucosa and enter the venous blood supply to complete an autoinnoculation cycle
• Filariform larvae enter humans often through the feet, get into venous blood, then to lungs, then migrate up bronchi and are swallowed
  • 18 to 28 days after initial infection, they enter the small bowel
• In the small bowel, adult female begins releasing eggs through parthogenesis (no male needed)

Epidemiology

• Endemic in the tropics, especially Jamaica, Haiti, Laos, Cambodia, Vietnam, and the beaches of western Africa
• May still be endemic in Appalachia, southeastern US, Europe, Australia, and Japan
• Has been transmitted through organ donation
• Infections can last years or decades

Risk Factors for Severe Disease

• Immune suppression
  • Prednisone (even one dose)
  • Transplant
  • Hematologic malignancy
  • HTLV-1
  • NOT HIV
• Diabetes mellitus
• Malnutrition
• Renal failure
• Chronic alcohol abuse

Clinical Presentation

Larva currens

• Itchy linear rash that can be watched spreading over hours (10 cm/h)
• From intradermal migration of the filariform larva
• Much faster than cutaneous larva migrans (caused by hookworm)

Intestinal strongyloidiasis

• Incubation period is about 2 weeks
• Most are asymptomatic, with or without fluctuating eosinophilia
  • Eosinophilia can be as high as 10-15% of leukocytes
  • Eosinophilia may not be present in immunocompromised patients
• GI symptoms, including weight loss, diarrhea, abdominal or epigastric pain, nausea, and vomiting
• Rarely pulmonary symptoms unless COPD
• May have larva currens or non-specific itchy rash, usually perianal

Hyperinfection syndrome

• Occurs in immunosuppressed patients, including post-transplant, GVHD, prolonged steroids, TNF-alpha inhibitors, heme malignancies, diabetes, and HTLV-1 infection (but not HIV)
• Still adheres to the usual gut-to-lung-to-gut cycle
• Polymicrobial bacteremia and infections secondary to colonic mucosal damage
  • Usually Gram-negatives, enterococci, and Bacteroides
• Often no eosinophilia (because immunosuppressed)

Disseminated strongyloidiasis

• Severe hyperinfection with dissemination of the larvae to any organ
• Not limited to gut and lung, can involve brain, kidneys, liver, etc
• Usually no eosinophilia

Diagnosis

• Stool O&P is 75% sensitive, so it's done three times to improve it to 90%
• Serology can be negative early in disease
  • Usually decreased or negative by 6 to 12 months after treatment
• Consider HTLV-1 coinfection
• If unwell, check for larvae in blood, sputum, CSF, and urine
• On colonoscopy, it can mimic ulcerative colitis

Management

• First-line: ivermectin 200 mcg/kg po daily for 2 days
  • Needs special access, as it it a veterinary medication
  • DO NOT use if onchocerciasis or loiasis
• Second-line: albendazole 400 mg po BID for 10-14 days, but not as effective
• Hyperinfection or dissemination:
  • Stop any immune-supressing medications
  • Ivermectin 200 mcg/kg po daily until stool O&P is negative for 2 weeks
• To confirm eradication, check feces up to 1 year after treatment, and serology 1 to 2 years after treatment
  • IgG should decline or serorevert 6 to 12 months after treatment
  • Eosinophilia (if present) should resolve
• HTLV-1 coinfection
  • May need to treat 2 days every 2 weeks to keep suppressed