Small intestine & ampulla

• Giardia intestinalis infection causes enterocyte damage and loss of brush border of the epithelial cells of the small intestine, which leads to shortening of microvilli and altered epithelial barrier function (Curr Top Med Chem 2018;18:1287)
• Mucosal alterations cause watery diarrhea, malabsorptive steatorrhea, nausea, abdominal pain, vomiting and weight loss
• Main consequence of Giardia colonization is nutrient malabsorption
• Most infections are asymptomatic

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Contributed by Centers for Disease Control and Prevention

Contributed by Iresha Vithanage, M.B.B.S., M.D., Saroona Haroon, M.B.B.S., Bobbi Pritt, M.D.,
Emily Fernholz, MLS (ASCP), Suhail Muzaffar, M.B.B.S. and Bilal Karim Siddiqui, M.D. (Case #157), Vidya Arole, M.B.B.S. and Wei Chen, M.D., Ph.D. (Case #543)

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Contributed by @JMGardnerMD on Twitter

• Trichrome with iron hematoxylin counterstain; methylene blue positively stains the trophozoites; Giemsa stain
• CD117 / KIT immunostain is positive (Hum Pathol 2009;40:323)

• J Pak Med Assoc 1994;44:206, J Clin Pathol 1990;43:641, Scand J Gastroenterol 1995;30:905

After a long hiking trip, most children in a large family group developed watery diarrhea, fatigue and stomach cramps along with bloating. At the hospital visit, the affected children told the doctor that they drank directly from the streams and river without the use of water purifier tablets or filters during the trip. Various tests were requested, including multiple stool samples collected over several days. Stool microscopy with direct fluorescent antibody testing (DFA) showed that the kids had giardiasis. If a duodenal biopsy is performed, which of the following is most likely to be true of the findings?

1. Deeper part of the small intestinal mucosa is frequently invaded by Giardia
2. Duodenal villous architecture can never be normal in this condition
3. Giardia organisms are pear shaped
4. Giardia organisms cannot be seen by light microscope
5. Immunohistochemical studies are mandatory for diagnosis

C. Giardia organisms are pear shaped. This is the correct answer as Giardia organisms can be described as pear shaped or as having a falling leaves appearance. Answer B is incorrect because the duodenal mucosa's villous architecture can be normal with organisms only floating on the surface in giardiasis. Answer E is incorrect because immunohistochemical studies, although utilized in some cases (such as CD117), are not mandatory in routine diagnosis of Giardia in biopsies. Answer A is incorrect because the organisms are usually found floating freely in the lumen between the duodenal villi, adhered to the mucosal surface or in the cytoplasm of the superficial epithelial cells but never in deeper parts of mucosal tissue. Answer D is incorrect because Giardia organisms are identifiable on light microscopy on routine H&E stain and are similar in size to duodenal epithelial cells (Int J Surg Pathol 2021;29:257, Hum Pathol 2009;40:323).

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Reference: Giardia lamblia

A 39 year old man presents to a general physician with malaise, episodic watery diarrhea and mild weight loss for the past 3 months. There is no significant past medical or surgical history. His vitals are stable, apart from mild tachycardia. On upper GI endoscopy, there was duodenal nodularity. Biopsy is taken with the clinical suspicion of celiac disease. The histopathological section image is given above. What is the diagnosis?

1. Celiac disease
2. Duodenal amebiasis
3. Duodenal giardiasis
4. Helicobacter pylori infection
5. These are nonspecific findings

C. Duodenal giardiasis, since the photomicrograph shows many Giardia organisms on the mucosal surface of small intestinal villi. Answer A is incorrect because in celiac disease, although the histological features can be simulated, there will be no Giardia organisms. Answer B is incorrect because in duodenal amebiasis, the morphology of the organisms is different; it is also very rare. Answer D is incorrect because in Helicobacter pylori infection, there will be V shaped / sea gull shaped or curved comma shaped tiny organisms. Answer E is incorrect because there are organisms on the surface of duodenal mucosa; therefore, these findings are not nonspecific (Int J Surg Pathol 2021;29:257).

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Reference: Giardia lamblia

In giardiasis patients, it is necessary to evaluate for which of the following additional diseases / pathologies?

1. Celiac disease - look for increased intraepithelial lymphocytes and villous blunting
2. Common variable immunodeficiency (CVID) - look for absence of plasma cells
3. Inflammatory bowel disease - look for granulomas
4. Primary melanoma - look for atypical cells

B. Common variable immunodeficiency (CVID) - look for absence of plasma cells. Checking for plasma cells in the lamina propria is recommended in patients with giardiasis as they are often seen in patients with CVID due to chronic giardiasis. Answers A, C and D are incorrect because giardiasis is not associated with any of these options.

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Reference: Giardia lamblia