Giardiasis -  Life Cycle

• Infection occurs by the ingestion of cysts in contaminated water or food.
• In the small intestine, excystation releases trophozoites that multiply by longitudinal binary fission.
• The trophozoites remain in the lumen of the proximal small bowel where they can be free or attached to the mucosa by a ventral sucking disk.
• Encystation occurs when the parasites transit toward the colon, and cysts are the stage found in normal (non diarrheal) feces.
• The cysts are hardy, can survive several months in cold water, and are responsible for transmission.
• Because the cysts are infectious when passed in the stool or shortly afterward, person-to-person transmission is possible.