Strongyloides hyperinfection — DTM&H MCQ

Correct answer: B — Strongyloides stercoralis hyperinfection

The correct answer is B, Strongyloides stercoralis hyperinfection. This ex-POW from Southeast Asia is a classic at-risk host: chronic, often decades-long, asymptomatic Strongyloides carriage via the autoinfective cycle is well documented in former prisoners of war and military personnel who served in the tropics. Starting prednisolone suppresses the Th2 immune response that normally contains the rhabditiform to filariform (L3) transformation, allowing massive, accelerated autoinfection (hyperinfection syndrome), which is exactly what the filariform larvae on stool microscopy indicate. Migrating filariform larvae physically breach the bowel wall carrying enteric flora with them, producing secondary gram-negative septicaemia (E. coli, Klebsiella), a hallmark complication of hyperinfection. This triad of steroid exposure, filariform larvae, and gram-negative sepsis in a patient with tropical exposure history is pathognomonic and mandates urgent ivermectin and screening of at-risk migrants before immunosuppression. Why the other options are wrong: B Ascaris hyperinfection: Ascaris does not have an autoinfective larval cycle and does not cause a steroid-triggered hyperinfection syndrome; its larvae are not the filariform (L3) form described in stool. C Hookworm reactivation: Hookworm larvae do not undergo internal autoinfection or reactivation with immunosuppression, and hookworm eggs, not filariform larvae, are typically seen in stool. D Schistosoma japonicum reactivation: Schistosomiasis is diagnosed by ova in stool or urine, not filariform larvae, and steroids do not precipitate a hyperinfective larval migration or gram-negative sepsis in this way. E Toxocara visceral larva migrans: Toxocara is a dead-end zoonotic infection in humans with no enteric autoinfective cycle, no filariform larvae in stool, and no steroid-induced bacteraemic complication. Key point: Filariform larvae in stool plus recent corticosteroid exposure plus gram-negative sepsis in anyone with past tropical residence (including ex-POWs) equals Strongyloides hyperinfection until proven otherwise.

Reference: Strongyloides stercoralis infection in the UK: a systematic review and meta-analysis of published cases, PMC (2024), https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11342261/