For which organism is the trophozoite the infective stage for humans?

For which organism is the trophozoite the infective stage for humans?

• A. Endolimax nana
• B. Giardia duodenalis
• C. Entamoeba coli
• D. Dientamoeba fragilis

Answer: (D)

This item centers on whether the infectious form of a protozoan is a cyst or a trophozoite. Several intestinal protozoa infect humans via cysts that survive in the environment and are ingested with contaminated water or food, such as Giardia duodenalis, Endolimax nana, and Entamoeba coli. Dientamoeba fragilis is different: it has no true cyst stage, and infection is established by ingesting viable trophozoites, often carried into the host by Enterobius vermicularis eggs. Because the infectious form for this organism is the trophozoite, it is the best answer.

This item centers on whether the infectious form of a protozoan is a cyst or a trophozoite. Several intestinal protozoa infect humans via cysts that survive in the environment and are ingested with contaminated water or food, such as Giardia duodenalis, Endolimax nana, and Entamoeba coli. Dientamoeba fragilis is different: it has no true cyst stage, and infection is established by ingesting viable trophozoites, often carried into the host by Enterobius vermicularis eggs. Because the infectious form for this organism is the trophozoite, it is the best answer.