NEMATODES – STRONGYLOIDES STERCORALIS

**NEMATODES – STRONGYLOIDES STERCORALIS **

definition – Strongyloides stercoralis is a small intestinal nematode that causes strongyloidiasis, ranging from silent infection to fatal disseminated disease

causes – ingestion of infective filariform larvae is rare; main route is skin penetration of larvae from contaminated soil, especially in warm, moist areas; fecal‑oral spread possible in overcrowded settings

types of infection – autoinfection (continuous internal cycle) → hyperinfection syndrome (massive increase of larvae in usual sites) → disseminated strongyloidiasis (larvae reach ectopic organs)

pathogenesis –

1. filariform larva penetrates skin (often foot) →
2. enters peripheral blood →
3. carried to right heart → lungs →
4. crosses alveolar wall, ascends bronchial tree →
5. swallowed, reaches duodenum →
6. matures to adult female (parthenogenetic) in mucosa →
7. produces eggs that hatch in lumen →
8. rhabditiform larvae emerge →
9. either passed in stool (free‑living cycle) or develop to filariform larvae →
10. filariform larvae either exit in feces or re‑penetrate intestinal wall/perianal skin → autoinfection loop

memory rhyme for steps 1‑5: “Skin, Blood, Lung, Cough, Swallow – the larva’s travel!”

morphology – adult female 2–4 cm long, 0.3 mm wide, thin, ribbon‑like; no male needed (parthenogenesis)
rhabditiform larva: short buccal cavity, straight tail, 0.2–0.4 mm
filariform larva: elongated body, pointed tail, 0.3–0.5 mm, infective form

life cycle –

1. rhabditiform larva in stool →
2. → develops to free‑living adult in soil →
3. → produces eggs →
4. → hatches to rhabditiform larva →
5. → → filariform larva (infective) →
6. → penetrates human skin →
7. → bloodstream → lungs → throat → swallowed → intestine → adult female → eggs → repeat

funny trick: “R‑F‑F‑S‑P – Rhabditiform to Free to Filariform to Skin to Person”

clinical features –

• most infections asymptomatic
• gastrointestinal: watery diarrhea, abdominal cramps, malabsorption, weight loss
• cutaneous: “larva currens” – rapidly moving, itchy, serpiginous rash near perianal area
• respiratory: cough, wheeze, dyspnea (especially during hyperinfection)
• eosinophilia common in chronic infection

complications –

• hyperinfection syndrome (massive larval burden in gut and lungs) → severe diarrhea, hemorrhage, respiratory failure
• disseminated strongyloidiasis (larvae in brain, liver, kidneys) → sepsis, meningitis, multiorgan failure
• secondary bacterial sepsis from gut flora translocation (Staphylococcus, Gram‑negative bacilli)

diagnosis –

• stool microscopy: fresh stool examined for rhabditiform/filariform larvae (multiple samples increase yield)
• agar plate culture: characteristic serpentine tracks of larvae
• serology: ELISA or Western blot for IgG antibodies (useful in chronic/low‑burden cases)
• duodenal/jejunal biopsy: adult females in mucosa (rare)
• sputum or BAL for larvae in hyperinfection

management –

• first‑line: ivermectin 200 µg/kg orally once daily for 2 days (extend to 5‑7 days in hyperinfection)
• alternative/older drug: thiabendazole 25 mg/kg three doses daily for 2 days (more side effects)
• severe cases: ivermectin via nasogastric tube or rectal enema, plus broad‑spectrum antibiotics for bacterial sepsis
• monitor eosinophil count and repeat stool exams to confirm cure

prevention –

• wear shoes in endemic areas → stop skin penetration
• improve sanitation, proper disposal of human feces → break fecal‑oral cycle
• avoid walking barefoot on moist soil, especially in tropical farms
• health education on personal hygiene and safe water

essential NCH points – autoinfection makes infection chronic; immunosuppressed (steroids, HTLV‑1) are at highest risk for hyperinfection; ivermectin is drug of choice for both uncomplicated and complicated disease.