Giardia lamblia

Giardia lamblia A parasite responsible for a common form of infectious diarrhea. The parasite lives in two stages: trophozoites and cysts. Trophozoites are the active form of the parasite inside the body. Cysts represent the resting stage that enables the parasite to survive outside the body. Infection begins from swallowing the Giardia cysts. The acid in the stomach activates the cysts, which in turn release the disease-causing trophozoites. The parasites attach to the lining of the small intestine, reproduce, and are swept down the intestine in the fecal stream. Cysts form in the lower intestines and are then passed in the feces. See also giardiasis.