Eggs or larvae recovered in the stool are not routinely used to diagnose infections caused by which helminth?

Eggs or larvae recovered in the stool are not routinely used to diagnose infections caused by which helminth?

• A. Strongyloides stercoralis
• B. Trichinella spiralis
• C. Necator americanus
• D. Ascaris lumbricoides

Answer: (B)

Stool-based diagnosis relies on the parasite releasing eggs or larvae into the intestinal lumen that are then shed in feces. Trichinella spiralis doesn’t follow that pattern. After ingestion of infected meat, the adult worms reside in the small intestine and release larvae that migrate to and encyst in muscle tissue. No eggs or larvae are routinely excreted in the stool, so stool microscopy isn’t used to diagnose Trichinella infections. Diagnosis is usually by muscle biopsy showing encysted larvae or serology for antibodies, along with relevant clinical signs.

In contrast, the other parasites listed do shed diagnostic stages in stool. Strongyloides stercoralis can be detected by finding larvae in stool. Necator americanus and Ascaris lumbricoides shed eggs that can be seen in stool samples.