Last updated: February 6, 2023

Summarytoggle arrow icon

Giardiasis is a common parasitic infection caused by the protozoan Giardia lamblia. Transmission usually occurs via the fecal-oral route (e.g., from contaminated drinking water) when traveling or living in an endemic region. Giardia live in two states: as active trophozoites in the human body and as infectious cysts surviving in various environments. Following the ingestion of the cyst, individuals may experience abdominal cramps and frothy, greasy diarrhea. Diagnosis of giardiasis involves analyzing stool for microscopic confirmation of cysts or trophozoites, and possibly immunoassays to detect antigens. Treatment is indicated in nonpregnant symptomatic individuals and usually consists of tinidazole.

Epidemiologytoggle arrow icon

  • Giardia lamblia is widespread throughout the world and affects ∼ 200 million people per year worldwide.
  • Incidence: estimated 5–8/100,000 per year in the US
  • In the US, giardiasis is the most common intestinal disease caused by parasites.

Epidemiological data refers to the US, unless otherwise specified.

Etiologytoggle arrow icon

  • Pathogen: Giardia lamblia; (also known as Giardia intestinalis or duodenalis), a protozoan [1]
  • Transmission [2]
    • Waterborne: from drinking recreational water (e.g., lakes, rivers, ponds, swimming pools)
    • Fecal-oral (e.g., through food handlers, people in daycare and nurseries, oral-anal sexual contact): Giardia cysts are passed into the environment from the feces of infected people and animals. [2][3]
    • Infection is more likely to occur after traveling to endemic regions such as the tropics, subtropics, and North-American mountain regions.

Pathophysiologytoggle arrow icon

  • Life cycle ; [1][4]
    • Giardia have 2 stages in the life cycle.
      1. Trophozoite: active form of the pathogen that multiplies, lives within the host's body
        • Morphology: long oval shape with two nuclei and four pairs of flagella that resemble a kite
      2. Cysts: excreted, infectious form of the pathogen, able to survive in moist environments
        • Morphology: oval, four nuclei
    • Ingestion of cysts → excystation and conversion to trophozoite form → rapid multiplication, adhesion to intestinal walls → encystation in large bowel → excretion of cysts → possible reinfection
  • Mechanism [5]

Clinical featurestoggle arrow icon

Infection with Giardia lamblia must be considered as a differential diagnosis for persistent diarrhea. [9]

To remember that GiARDia causes fatty DIarrhea, think “Gee, Arty has fatty stools.”

Diagnosticstoggle arrow icon

Treatmenttoggle arrow icon

  • First-line [11]
    • Tinidazole (single oral dose): studies have shown it has fewer side effects, higher cure rates, and a lower antibiotic resistance rate than other agents
    • Nitazoxanide (three day course)
  • Alternatives

Referencestoggle arrow icon

  1. Parasites - Giardia - Illness & Symptoms. Updated: July 21, 2015. Accessed: May 9, 2017.
  2. Parasites - Giardia - Diagnosis & Detection. Updated: July 21, 2015. Accessed: January 4, 2018.
  3. Shane AL, Mody RK, Crump JA, et al. 2017 Infectious Diseases Society of America Clinical Practice Guidelines for the Diagnosis and Management of Infectious Diarrhea. Clin Infect Dis. 2017; 65 (12): p.e45-e80.doi: 10.1093/cid/cix669 . | Open in Read by QxMD
  4. Parasites - Giardia - Pathogen & Environment. Updated: February 16, 2017. Accessed: January 4, 2018.
  5. Adam RD. Biology of Giardia lamblia. Clin Microbiol Rev. 2001; 14 (3): p.447-475.doi: 10.1128/cmr.14.3.447-475.2001 . | Open in Read by QxMD
  6. Troeger H, Epple H-J, Schneider T, et al. Effect of chronic Giardia lamblia infection on epithelial transport and barrier function in human duodenum. Gut. 2007; 56 (3): p.328-335.doi: 10.1136/gut.2006.100198 . | Open in Read by QxMD
  7. Yel L . Selective IgA deficiency. J Clin Immunol. 2010; 30 (1): p.1-16.doi: 10.1007/s10875-009-9357-x . | Open in Read by QxMD
  8. Chapel H, Cunningham-Rundles C. Update in understanding common variable immunodeficiency disorders (CVIDs) and the management of patients with these conditions. Br J Haematol. 2009; 145 (6): p.709-727.doi: 10.1111/j.1365-2141.2009.07669.x . | Open in Read by QxMD
  9. Immunodeficiency. Updated: January 1, 2020. Accessed: July 13, 2020.
  10. Parasites - Giardia - Sources of Infection & Risk Factors. Updated: July 21, 2015. Accessed: May 9, 2017.
  11. Shelton AA. Sexually Transmitted Parasitic Diseases. Clinics in Colon and Rectal Surgery. 2004; 17 (04): p.231-234.doi: 10.1055/s-2004-836943 . | Open in Read by QxMD

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