Giardia lamblia belongs to the flagellates. Its name has often been changed; some clinicians still call it Lamblia intestinalis. The parasite can be found in every part of the world. A number of similar species in animals have been described, but it is still a question whether the mouse or the rat can be a host of the type of Giardia found in human beings. The incidence of the parasite was estimated at 12 per cent in the United States by Hegner and at about 10 per cent in Hungary by Lörincz.1 The infection is more common among children than among adults.
Giardia lamblia has a vegetative and a cystic stage. The vegetative form is pear shaped, about 14 microns in length and 8 microns in diameter, with two symmetric sides. Each side has a nucleus and four free flagella. The axostyle is crossed by a typical parabasal body.