An intestinal parasite seen in an iodine-stained fecal wet mount described as 25 μm in diameter with a central body and a ring of cytoplasm containing nuclei; best describes which organism?

• A. Blastocystis hominis
• B. Endolimax nana
• C. Entamoeba dispar
• D. Lodamoeba butschlii

Answer: (A)

Recognizing a vacuolated intestinal protozoan on an iodine-stained fecal mount is key here. Blastocystis hominis often appears as a relatively large cell with a prominent central body (central vacuole) and a surrounding ring of cytoplasm that contains nuclei. The overall size can reach around 25 μm, which matches the description, and the central vacuole with peripheral cytoplasm is a classic look for this organism in stool preparations.

The other organisms have different morphologies: Endolimax nana is smaller and lacks a large central vacuole with a peripheral ring; Entamoeba dispar and related amoebae are typically 10–15 μm with a single nucleus and do not show a central vacuole surrounded by a cytoplasmic ring; Lodamoeba butschlii has distinct amoeboid features that don’t fit the described vacuolated, ring-with-nuclei appearance.