Giardia

Giardia duodenalis (or Giardia lamblia or Giardia intestinalis) is a single celled animal, i.e., a protozoan, that moves with the aid of several flagella. It is sometimes referred to as Lamblia intestinalis. It is the causative agent of giardiasis, an infection of the small intestine and the most frequent cause of nonbacterial diarrhea in North America.