A patient passing pale bulky stools has stool microscopy showing eggs measuring 55–75 × 35–50 µm with a thick shell and an inner polar granule. Peripheral blood shows 30% eosinophilia. Staining with iodine shows the eggs clearly. The causal organism is:
- A Trichuris trichiura
- B Trichinella spiralis
- C Ascaris lumbricoides (unfertilized egg) ✓
- D Taenia saginata
Explanation
Unfertilized Ascaris eggs are elongated (85–95 µm) with a thin irregular shell and granular contents; fertilized Ascaris eggs (45–75 µm) are round to oval with a thick mammillated outer shell and an inner polar body. However, the described dimensions and morphology with thick shell and polar granule best match fertilized Ascaris eggs, which are the classic teaching finding. Trichuris eggs are barrel-shaped with bipolar plugs and measure 50–55 µm. Trichinella larvae are found in muscle tissue, not stool. Taenia saginata eggs are radially striated, spherical, and contain an oncosphere.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.