Pathophysiology of Giardiasis

Giardia cyst

Giardia trophozoite, after
process of Excystation

          

In the colon, Giardia cyst undergo excystation and develop into trophozoite that will develop tails called flagella. The trophozoite will then invade the enterocytes at microvillus-covered surface of the duodenum and jejunum.

When they reach the enterocytes, the trophozoite uses special disk on their ventral side to attach to enterocyte and with the help from lectin on surface of Giardia to bind with sugar found on the surface of enterocyte.

Attachment of Giardia trophozoite to enterocytes will cause changes to the architecture of the villous at jejunum and duodenum then cause malabsorption.

Trophozoite that attached at enterocyte will reproduce and multiply to produce more trophozoite at the site of attachment.

This multiplication will create physical barrier between intestinal lumen and enterocytes that will further interfere with nutrient lead to severe nutrient malabsorption.

Multiplication of trophozoites eventually lead to enterocytes damage, villi atrophy, cysts hyperplasia and intestinal hyperpermeability brush border damage that causes a reduction in disaccharidase enzyme secretion.

Besides disaccharidase, other cytopathic substances such as lectins, glycoproteins and proteinases may cause direct damage to intestinal mucosa.

Giardia trophozoites only infect intestinal lumen and not other areas such as surrounding tissue and bloodstream.

Study has shown that Giardia trophozoite can induce cell apoptosis by activating intrinsic and extrinsic pathway, down regulation of antiapoptotic protein Bcl-2 and up regulation of proapoptotic Bax that is strongly associated with induction of cell apoptosis.

REVIEW OF GIARDIASIS PATHOPHYSIOLOGY