Stool examination of an asymptomatic carrier shows quadrinucleate cysts measuring 10 to 15 micrometres that are morphologically indistinguishable from Entamoeba histolytica cysts. Which method can reliably differentiate this organism from pathogenic E. histolytica?

• A Measurement of cyst size by calibrated micrometry
• B Stool antigen detection assay specific for E. histolytica ✓
• C Counting the number of nuclei in the mature cyst
• D Observation of glycogen vacuoles in iodine preparation

Explanation

Entamoeba dispar is morphologically identical to E. histolytica at every stage, including cyst size and tetranucleate mature cysts, so microscopy alone cannot separate them. Differentiation requires species-specific methods such as E. histolytica antigen detection ELISA or PCR. This matters clinically because E. dispar is non-pathogenic and carriage needs no treatment. Nuclear count distinguishes mature from immature cysts within both species, and glycogen vacuoles appear transiently in immature cysts of both species as well.

Reference: Paniker's Textbook of Medical Parasitology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.