JOHN BAVOSI / SCIENCE PHOTO LIBRARY JOHN BAVOSI / SCIENCE PHOTO LIBRARY
Illustration of the parasite Giardia lamblia, a single-celled protozoan that causes the human intestinal disorder giardiasis (known also as lambliasis). Here, the motile trophozoite stage is seen with its four sets of flagellae; it has two nuclei (at top, purple). Most common in tropical areas, Giardia lamblia is acquired in unhygienic conditions, from contaminated water or food, or by direct contact with a sufferer. Swallowed cysts hatch into this trophozoite stage, which attaches by means of sucking discs to microvilli in the human intestine. The result is abdominal discom- fort, cramps, attacks of diarrhoea, and nausea. Drug treatment may be necessary.
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