Giardia lamblia (PCR): the pathway in the body

Giardia lamblia (PCR) is part of the pathway “Intestinal parasites”. This page shows the whole pathway; the station of Giardia lamblia (PCR) is highlighted.

Where this laboratory value sits: Forms in the stool — DNA detected by PCR. Most of these organisms form a wall again and leave the body with the stool. A PCR test looks for sections of their DNA there and so shows which species is present. Source 1, 4, 5

In brief

Intestinal parasites are single-celled organisms such as Giardia lamblia, Entamoeba histolytica or Cryptosporidium. They reach the gut as a dormant form, hatch there and later shed new cysts with the stool.

The pathway step by step

1. Cysts, oocysts → Excystation · Stomach acid, Bile salts Stomach acid, body warmth and bile salts are the signal to open the wall. The motile forms hatch in the small intestine. Source 1, 2
2. Excystation → Active form Giardia lamblia, Entamoeba histolytica, Blastocystis and Dientamoeba fragilis live in the gut as trophozoites. In Cryptosporidium and Cyclospora, the hatching form is called a sporozoite. Source 1, 2, 5, 6
3. Active form → Attachment Giardia holds on to the cell surface with an adhesive disc. Entamoeba binds to sugar chains of the mucus layer via a lectin. Cryptosporidium and Cyclospora enter the gut cell. Source 1, 2, 3
4. Attachment → Multiplication In the gut, the single-celled organisms divide. Cryptosporidium and Cyclospora pass through several forms in succession, including a sexual stage. Source 2, 4
5. Multiplication → Forms in the stool Encystation Most of these organisms form a wall again and leave the body with the stool. A PCR test looks for sections of their DNA there and so shows which species is present. Source 1, 4, 5
6. Mucosa → Dendritic cells Dendritic cells pick up fragments of the organisms and present them to T cells in the lymphoid tissue of the gut wall. Source 7
7. Dendritic cells → T cells T cells coordinate the response: they release signalling molecules that attract further immune cells, and they prompt B cells to form antibodies. Source 7
8. T cells → IgA in the gut B cells form antibodies of the IgA class. These are released through the gut wall into the mucus, where they bind to the surface of the organisms. Source 7

Cofactors in this pathway

• Gastric acid (protons) — The acidic stomach content is one of the signals that opens the wall of the dormant form Source 1, 2
• Bile salts — The second signal for hatching in the small intestine, besides warmth and acid Source 1, 2In the ORY catalogue as a laboratory value: Gallensäuren (Stuhl)
• Cholesterol — Giardia does not make it itself; when the supply in the gut falls, cyst wall formation starts Source 8
• Vitamin A — Retinoic acid is formed from it and makes gut B cells switch to the IgA class Source 9
• Vitamin D — The active form makes maturing B cells express the homing receptor CCR10 Source 10In the ORY catalogue as a laboratory value: Vitamin D

Sources

1. Einarsson E, Ma'ayeh S, Svärd SG. An up-date on Giardia and giardiasis. Curr Opin Microbiol 2016 · PubMed 27501461
2. Tzipori S, Griffiths JK. Natural history and biology of Cryptosporidium parvum. Adv Parasitol 1998 · PubMed 9554069
3. Mann BJ. Structure and function of the Entamoeba histolytica Gal/GalNAc lectin. Int Rev Cytol 2002 · PubMed 12049210
4. Almeria S, Cinar HN, Dubey JP. Cyclospora cayetanensis and Cyclosporiasis: An Update. Microorganisms 2019 · PubMed 31487898
5. Stark D, Barratt J, Chan D et al. Dientamoeba fragilis, the Neglected Trichomonad of the Human Bowel. Clin Microbiol Rev 2016 · PubMed 27170141
6. Tan KS. New insights on classification, identification, and clinical relevance of Blastocystis spp. Clin Microbiol Rev 2008 · PubMed 18854485
7. Fink MY, Singer SM. The Intersection of Immune Responses, Microbiota, and Pathogenesis in Giardiasis. Trends Parasitol 2017 · PubMed 28830665
8. Luján HD, Mowatt MR, Byrd LG et al. Cholesterol starvation induces differentiation of the intestinal parasite Giardia lamblia. Proc Natl Acad Sci U S A 1996 · PubMed 8755526
9. Mora JR, von Andrian UH. Role of retinoic acid in the imprinting of gut-homing IgA-secreting cells. Semin Immunol 2009 · PubMed 18804386
10. Shirakawa AK, Nagakubo D, Hieshima K et al. 1,25-dihydroxyvitamin D3 induces CCR10 expression in terminally differentiating human B cells. J Immunol 2008 · PubMed 18292499

Whole pathway: Intestinal parasites

As of 2026-09-16. Draft, written by Claude to schema v2; sources checked in PubMed; expert approval pending
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