In Giardia, ingestion of cysts converts to what stage in the duodenum?

• A. Giardia Intestinalis Cyst
• B. Giardia Intestinalis Trophozoite Stage
• C. Trichomonas vaginalis trophozoite
• D. Plasmodium species

Answer: (B)

The key idea is that Giardia cysts are the dormant infectious form, and when they reach the duodenum they undergo excystation to release the active, motile trophozoite stage. These trophozoites are the replicating form that colonizes the small intestine after ingestion, attaching to the mucosa as they multiply. Later, they can encyst again as they move toward the colon to be shed in feces, continuing the life cycle. So, after ingesting cysts, the stage that appears in the duodenum is the trophozoite stage. The cyst itself is the form you ingest, and the other organisms mentioned are not part of Giardia’s life cycle.