Introduction

Although there have been more than 40 species described in the genus Giardia, most of these have now been divided into 3 distinct morphologic groups, the largest of which, containing 20 formerly described species fall into the “duodenalis” group, are found mainly in mammals and a few from birds. Giardia duodenalis  (also called G. lamblia and G. intestinalis) falls into this group and is classified in the domain Eukarya, kingdom Protista, Phylum Sarcomastigophora, subphylum Zoomastigophora, Class Zoomastogophorea, Order Diplomonadida. The members of this subphylum, both free-living and parasitic, are commonly called animal-like (or non-photosynthetic) flagellates.