Which is the largest intestinal protozoan to infect humans?

Which is the largest intestinal protozoan to infect humans?

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

Answer: (C)

Balantidium coli is the largest intestinal protozoan that infects humans. It’s a ciliate, and its trophozoite is quite large—often tens to over a hundred micrometers long—with a thick-walled cyst also relatively large. By comparison, Giardia lamblia trophozoites are about 10–15 μm, Entamoeba histolytica ranges roughly 12–60 μm, and Dientamoeba fragilis is about 5–12 μm. The noticeable size difference makes Balantidium coli stand out as the largest intestinal protozoan in humans. It’s distinguished taxonomically by its cilia and its characteristic macronucleus, and infection occurs through ingestion of cysts, commonly linked to pigs.

Balantidium coli is the largest intestinal protozoan that infects humans. It’s a ciliate, and its trophozoite is quite large—often tens to over a hundred micrometers long—with a thick-walled cyst also relatively large. By comparison, Giardia lamblia trophozoites are about 10–15 μm, Entamoeba histolytica ranges roughly 12–60 μm, and Dientamoeba fragilis is about 5–12 μm. The noticeable size difference makes Balantidium coli stand out as the largest intestinal protozoan in humans. It’s distinguished taxonomically by its cilia and its characteristic macronucleus, and infection occurs through ingestion of cysts, commonly linked to pigs.