Which trophozoite is suspected if ingested red cells are seen on a saline wet mount?

Which trophozoite is suspected if ingested red cells are seen on a saline wet mount?

• A. Giardia lamblia
• B. Entamoeba histolytica
• C. Entamoeba coli
• D. Dientamoeba fragilis

Answer: (B)

Red blood cell ingestion by a trophozoite is a hallmark of Entamoeba histolytica. When this parasite invades the intestinal mucosa, its trophozoites actively phagocytose host cells, including erythrocytes, which you can sometimes observe inside the trophozoite on a saline wet mount or stained smear. This feature helps distinguish it from other intestinal amoebae and from Giardia lamblia, which has a distinct pear-shaped trophozoite with two nuclei and does not ingest red cells. Entamoeba coli and Dientamoeba fragilis lack this red-cell–ingesting trophozoite behavior, so seeing red cells inside a trophozoite on a wet mount strongly points to Entamoeba histolytica. This finding supports invasive amebiasis and can guide confirmation with antigen testing or molecular assays if needed.

Red blood cell ingestion by a trophozoite is a hallmark of Entamoeba histolytica. When this parasite invades the intestinal mucosa, its trophozoites actively phagocytose host cells, including erythrocytes, which you can sometimes observe inside the trophozoite on a saline wet mount or stained smear. This feature helps distinguish it from other intestinal amoebae and from Giardia lamblia, which has a distinct pear-shaped trophozoite with two nuclei and does not ingest red cells. Entamoeba coli and Dientamoeba fragilis lack this red-cell–ingesting trophozoite behavior, so seeing red cells inside a trophozoite on a wet mount strongly points to Entamoeba histolytica. This finding supports invasive amebiasis and can guide confirmation with antigen testing or molecular assays if needed.