Strongyloidiasis: Causative Organism Characteristics
The correct answer is C: Hyperinfection is a complication of the causative organism (Strongyloides stercoralis). This patient's presentation of abdominal discomfort, serpiginous urticarial rash (larva currens), barefoot walking history, and rhabditiform larvae in stool is classic for strongyloidiasis, and hyperinfection syndrome represents its most life-threatening complication 1.
Why Hyperinfection is the Correct Answer
Hyperinfection syndrome occurs due to the unique autoinfection capability of S. stercoralis, where the parasite can replicate and increase in numbers without leaving the host. 1 This distinguishes strongyloidiasis from other helminthic infections and creates the potential for overwhelming infection decades after initial acquisition 1.
Key Features of Hyperinfection:
- Immunosuppression triggers catastrophic disease, particularly corticosteroid therapy, which is the most common precipitant 1, 2
- Massive larval invasion of the gastrointestinal tract and lungs occurs, with potential dissemination to other organs 2, 3
- Fatal outcomes are common if unrecognized, with larvae piercing the bowel wall and causing gram-negative bacteremia from enteric flora translocation 2
- Eosinophilia may be absent during hyperinfection, making diagnosis more challenging 1
Why the Other Options are Incorrect
Option A: Rhabditiform larvae is NOT the infective stage
- Filariform larvae are the infective stage, not rhabditiform larvae 4
- Rhabditiform larvae are the non-infective form excreted in feces 4
- These rhabditiform larvae can develop into filariform larvae in soil OR directly in the gut (causing autoinfection) 4, 3
Option B: Humans are the DEFINITIVE host, not intermediate
- Humans serve as the definitive host where parasitic females reside in the small intestine and reproduce via parthenogenesis 4
- There is no intermediate host required in the S. stercoralis life cycle 4
Option D: Adult worms reside in the SMALL INTESTINE, not caecum
- Adult parasitic females reside in the small intestine, specifically the duodenum and jejunum 4, 5
- The caecum is not the primary location for S. stercoralis adult worms 4
Critical Clinical Implications
Screening for strongyloidiasis before initiating immunosuppression is essential to prevent hyperinfection syndrome. 1, 6 This patient's history of walking barefoot in endemic areas warrants:
- Serological testing (sensitivity >80%) as the primary diagnostic method, since single stool examination has low sensitivity 1, 6
- Treatment with ivermectin 200 μg/kg for 2 consecutive days before any corticosteroid therapy 7, 8
- Avoidance of corticosteroids until strongyloidiasis is excluded or treated, as this can precipitate fatal hyperinfection 6, 7
The serpiginous rash (larva currens) this patient exhibits is pathognomonic for strongyloidiasis, representing rapid larval migration through the skin at several millimeters per second 7.