Which nematode is capable of autoinfection and can cause hyperinfection syndrome?

• A. Trichinella spiralis
• B. Strongyloides stercoralis
• C. Ascaris lumbricoides
• D. Enterobius vermicularis

Answer: (B)

The concept being tested is the unique ability of certain helminths to reinfect the same host from within, leading to potential widespread disease when immunity is suppressed. Strongyloides stercoralis can complete part of its life cycle inside the human host: some larvae in the gut can molt into infective filariform larvae that penetrate the intestinal wall or perianal skin, causing autoinfection. This allows the infection to persist for years and can escalate into hyperinfection syndrome, especially under immunosuppression such as corticosteroid use or HTLV-1 infection. In hyperinfection, the number of larvae increases and they disseminate to multiple organs, causing severe GI and pulmonary symptoms and risk of sepsis from translocated gut bacteria.

Trichinella spiralis is acquired by eating undercooked meat and the larvae encyst in muscle tissue, not by autoinfection in the gut. Ascaris lumbricoides involves ingestion of eggs that hatch and migrate through the lungs before returning to the intestine; it does not rely on autoinfection within the same host to cause hyperinfection. Enterobius vermicularis causes perianal itching and reinfection mainly through scratching and autoinfection is not associated with a disseminated, life-threatening hyperinfection syndrome.