Giardia lamblia is a protozoan parasite that has a worldwide distribution;in the United States and most other highly industrialized countries, it is the intestinal parasite identified most commonly. G lamblia was identified in 1681 by Von Leewenhock in his stools, and for centuries it was thought to represent a nonpathogenic organism. In the past 20 years, however, data have accumulated demonstrating that, at times, G lamblia can be a pathogen,causing disease in both sporadic and epidemic forms. Nevertheless, the majority of human infections are asymptomatic.

G lamblia is a flagellated protozoa that has two life cycle stages: trophozoite and cyst. The trophozoite usually is seen in preparations of duodenal mucosa or fresh diarrheic stools. It is pear-shaped and dorsally convex with a spiral organelle, the sucking disk, on the ventral surface, which is its mode of attachment to the mucosal surface. The trophozoite is 10 to 21 mcm in length...

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