Pathology of Giardiasis

Dr Sampurna Roy MD

Giardiasis is a small intestinal infection caused by the protozoa Giardia duodenalis (also referred to as Giardia lamblia and Giardia intestinalis).

 Giardia duodenalis is a pear or sickle shaped, binucleate protozoa.

Giardia exists as infectious cysts in contaminated food and water which spread by fecal-oral route and as trophozoites which multiply in the intestinal lumen and cause disease.

Clinical presentation:  

Usually asymptomatic. May present with epigastric or right upper quadrant pain and persistent steatorrhoea. Increase in severity of the case correlate with factors such as achlorhydria and low secretary IgA level (agammaglobulinemic patients)
 

How does it differ from Entamoeba histolytica?

Giardia duodenalis trophozoites are pear-shaped,have two nuclei and are flagellated.

Reside in the duodenum rather than colon.

Adhere to the intestinal epithelial cell rather than invading the epithelium, thus causing diarrhoea rather than dysentery.

Mode of action:  

The trophozoites adhere to the sugars on the intestinal epithelial cells via parasite lectin which is activated when cleaved by proteases. Tight contact is made between parasite and intestinal epithelial cell via sucker-like disc.
Giardia block nutrient absorption by covering the surface of the epithelial cells or by damaging the microvilli.

Histologic features:

One or two duodenal punch biopsy specimens are adequate for diagnosis (site of colonization of organism may vary ).

Diagnostic feature: Identification of sickle shaped organism attached to the surface or free within the mucus layer.

Biopsy features range from normal to abnormal appearance of the intestinal mucosa.

Mucosal changes are minimal in most cases.

In some cases here may be clubbing of villus and decreased villus-crypt ratio.

Crypt hyperplasia and focal epithelial damage may be noted.

An increased mononuclear infiltrate may be present in the lamina propria.

There may be increased intraepithelial lymphocytes.

The brush border of the absorptive cells may be irregular.

Sometimes villi may be absent and resemble atrophic stage of gluten-induced enteropathy.

In case of immunodeficient patients, the histopathologist should look for plasma cells in the lamina propria.

Nodular follicular hypertrophy of the mucosal lymphoid tissue is associated with common variable immunodeficiency. 

Crypt cell loss and apoptosis may be noted in HIV (human immunodeficiency virus) positive cases.

Further reading:

Giardiasis: a histologic analysis of 567 cases.

Histologic detection of trophozoites of Giardia lamblia in the terminal ileum.

Human giardiasis. A morphometric study of duodenal biopsy specimens in relation to the trophozoite count in the duodenal aspirate.

Giardiasis: analysis of histological changes in biopsy specimens of 80 patients.