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 |