A stool sample from a child with vague abdominal pain shows spherical, bile-stained eggs measuring about 60 micrometres, surrounded by a thick outer coat with a coarse, wavy, mammillated albuminous surface. The adult form of this parasite is characterised by:

• A A buccal capsule with cutting plates used to anchor to the jejunal mucosa
• B Being the largest intestinal nematode, with three prominent lips at the anterior end ✓
• C A whip-like anterior third embedded in the caecal mucosa
• D An arrowhead-shaped egg with a lateral spine

Explanation

The mammillated, bile-stained fertilised egg is diagnostic of Ascaris lumbricoides, the largest intestinal nematode, reaching 20 to 35 cm in length. Its anterior end bears three prominent lips. Cutting plates belong to Necator americanus, whose eggs are thin-shelled with a clear space between shell and embryo, quite different from the mammillated Ascaris egg. The whip-like anterior end describes Trichuris trichiura, and lateral-spined eggs describe Schistosoma mansoni.

Reference: Paniker's Textbook of Medical Parasitology, 9th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.