Genus: Giardia

Introduction

• Species of giardia are pyriform to elliptical in shape and bilaterally symmetrical
• Anterior end is broadly rounded and posterior end is drawn out and somewhat pointed
• Dorsal side is convex and large sucking disc is present on ventral side
• There are two anterior nuclei, two slender median axostyles, eight flagella arranged in four pairs and a pair of darkly stained bodies placed medially
• Cysts are produced which are oval or elliptical and possess two or four nuclei and number of familiar remnants of trophozoite organelles

Note: Species of Giardia  occurring in vertebrates have similar morphology. At least 10 species have been distinguished on basis of light microscopic characteristic and more recently using molecular methods; species are group into assemblages, system which is still Evolving.

Life cycle

• Simple and direct life cycle
• Trophozoite stage divide by binary fission to produce further trophozoite
• Trophozoite encyst forming resistant cyst stages
• Cyst are passed out in faceces of host