A 7-year-old child from a daycare center presents with foul-smelling, greasy stools, abdominal bloating, and failure to thrive. Stool microscopy reveals pear-shaped trophozoites with two nuclei and four flagella. Which organism is responsible?

• A Cryptosporidium parvum
• B Isospora belli
• C Entamoeba histolytica
• D Giardia lamblia ✓

Explanation

Giardia lamblia trophozoites are characteristically pear-shaped (teardrop), bilaterally symmetrical, with two nuclei giving an 'owl-eye' appearance and four pairs of flagella. It causes malabsorptive diarrhea with steatorrhea in children and daycare outbreaks. Cryptosporidium appears as acid-fast oocysts on stool; Entamoeba trophozoites are motile with ingested RBCs; Isospora oocysts are ellipsoidal and acid-fast.

Reference: Jawetz, Melnick, and Adelberg's Medical Microbiology, 28th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.