Answer: Giardiasis

Histology: The villi within this duodenal biopsy show slight villous blunting and evidence of epithelial injury. Plasma cells are decreased, which reflects the patient’s clinical history of common variable immunodeficiency syndrome. Focally, one identifies the trophozoites of Giardia along the surface of the epithelial cells and in the lumen. The trophozoites have a sickle to pear shape, with prominent paired nuclei and flagella.

Discussion: Cryptosporidium would appear as small blue dots adherent to the mucosal epithelial surface. Strongyloides would yield eggs and larvae within the lamina propria. Microvillus inclusion disease would be characterized by an absence of a crisp brush border on PAS staining. This condition is incompatible with prolonged life without an intestinal transplant.

Giardia is common, especially in underdeveloped countries or where the water supply becomes easily contaminated. The bowel histology may range from normal to a pattern of villous blunting with epithelial injury, so it is always important to examine the lumen of a GI biopsy for these parasites, particularly when a history of diarrhea is provided. Diff-Quick or trichrome stains can help identify the organism. The organism must be distinguished from the more common mucus fragments and squamous cell debris which may be in the bowel lumen.