Introduction

Giardia lamblia is a flagellate of world wide distribution. It is more common in warm climates than temporal climates.  It is the most common flagellate of the intestinal tract.

Morphology

The cysts of Giardia lamblia are 8 - 12 mm in size and are ellipsoid  in shape.  They contain 4 nuclei which do not tend to be obvious.  Longitudinal fibrils consisting of the remains of axonemes and parabasal bodies may also be seen.  Cysts may appear to shrink from the cell wall.

A cyst of Giardia lamblia stained with iodine

The trophozoites of Giardia lamblia are pear shaped and are an average size of 9 - 20 mm.  When stained, the trophozoite is seen to have 2 nuclei, 2 slender median rods (axostyles), and 8 flagella arising from the anterior end.  The movement of the trophozoite is described as tumbling leaf motility.

Clinical Disease

Giardia lamblia colonises the small intestine where the trophozoites adhere to the mucosal surface by means of their sucking disc.  Cysts are produced as the parasites descend the intestinal tract although trophozoites can be passed in the faeces in severe infections .  Giardia lamblia is transmitted through ingestion of cysts in contaminated water or food.  The main symptoms are abdominal pain, flatulence, and episodic diarrhoea with steatorrhea in severe cases.  However 50% of Giardia lamblia infections are symptomless.

Diagnosis

Cysts can be found by examination of the deposit of a formol-ether concentrate of a stool preparation.  Cysts may be excreted intermittently, therefore it is important to examine more than one stool.

Trophozoites are found by examination of saline wet preparations of fresh, diarrhoeic stool, duodenal or jejunal aspirate or in a permanently stained faecal preparation .

Trophozoites can also be found in the jejunal aspirate.  These can be recovered by the String Test or Enterotest capsule and the material examined microscopically for motile trophozoites.