Which finding supports Entamoeba histolytica over Entamoeba dispar in a stool sample?

• A. Erythrophagocytosis in trophozoites
• B. Cysts with four nuclei
• C. Acid-fast staining of oocysts in stool
• D. Perianal tape test positive

Answer: (A)

The key idea is that the pathogenic Entamoeba histolytica trophozoites uniquely ingest red blood cells, a process called erythrophagocytosis. Seeing trophozoites with visible red blood cells inside their cytoplasm in a stool sample strongly supports infection with E. histolytica, because E. dispar does not exhibit this RBC ingestion and is considered nonpathogenic. This feature ties directly to invasive disease and distinguishes the two species in microscopy.

Cysts with four nuclei can be seen with Entamoeba species but don’t reliably separate histolytica from dispar. Acid-fast staining of oocysts highlights coccidian parasites such as Cryptosporidium, not Entamoeba. A positive perianal tape test indicates Enterobius vermicularis, not Entamoeba.