Small intestine & ampulla

Infectious disorders

Giardia lamblia

Last author update: 1 August 2012
Last staff update: 10 November 2022 (update in progress)

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PubMed Search: Giardia lamblia[TI] small bowel[mh]

Hanni Gulwani, M.B.B.S.
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Cite this page: Gulwani H. Giardia lamblia. website. Accessed February 3rd, 2023.
Definition / general
  • Protozoan infection associated with malabsorption, chronic diarrhea
  • Spreads by fecally contaminated water, common in underdeveloped countries
  • Affects 1/3 of homosexual men in urban communities
  • Attaches to mucosa but does not invade
  • May cause endoscopic duodenal nodularity (Indian J Pathol Microbiol 2011;54:312)
  • Causes epithelial barrier dysfunction by down regulating claudin1 and increasing epithelial apoptoses (Gut 2007;56:328)
Diagrams / tables

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Life cycle

  • Detect cysts, trophozoites or antigens in stool
Gross images

Contributed by Centers for Disease Control and Prevention


Microscopic (histologic) description
  • Variable villous blunting, increased inflammatory cells, organisms are teardrop (pear) shaped with paired nuclei in lumen between villi
  • Size of organism is similar to enterocyte nuclei
Microscopic (histologic) images

Contributed by Bobbi Pritt, M.D., Emily Fernholz and Case #157

Trichrome stained stool specimen, Giardia duodenalis


Giardial trophozoites
along the surface of
foveolar epithelial cells

Sickle shaped trophozoites

Positive stains

"Falling leaf" motion of trophozoite

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