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DPDx

DPDx is an education resource designed for health professionals and laboratory scientists. For an overview including prevention and control visit www.cdc.gov/parasites/giardia.

Giardiasis

[Giardia duodenalis (syn. G. lamblia, G. intestinalis)]

G. duodenalis cysts in a wet mount stained with iodine.

Giardia duodenalis cyst in a wet mount stained with iodine.


G. duodenalis cysts stained with trichrome.

G. duodenalis cyst stained with trichrome.


G. duodenalis trophozoites stained with trichrome.

G. duodenalis trophozoite stained with trichrome.

Causal Agents

Giardia duodenalis is a protozoan flagellate (Diplomonadida).

Life Cycle:

Life cycle of giardia

Cysts are resistant forms and are responsible for transmission of giardiasis. Both cysts and trophozoites can be found in the feces (diagnostic stages) The number 1. The cysts are hardy and can survive several months in cold water. Infection occurs by the ingestion of cysts in contaminated water, food, or by the fecal-oral route (hands or fomites) The number 2. In the small intestine, excystation releases trophozoites (each cyst produces two trophozoites) The number 3. Trophozoites multiply by longitudinal binary fission, remaining in the lumen of the proximal small bowel where they can be free or attached to the mucosa by a ventral sucking disk The number 4. Encystation occurs as the parasites transit toward the colon. The cyst is the stage found most commonly in nondiarrheal feces The number 5.  Because the cysts are infectious when passed in the stool or shortly afterward, person-to-person transmission is possible. While animals are infected with Giardia, their importance as a reservoir is unclear.

Geographic Distribution:

Worldwide, more prevalent in warm climates, and in children.

Clinical Presentation

The spectrum varies from asymptomatic carriage to severe diarrhea and malabsorption. Acute giardiasis develops after an incubation period of 1 to 14 days (average of 7 days) and usually lasts 1 to 3 weeks. Symptoms include diarrhea, abdominal pain, bloating, nausea, and vomiting. In chronic giardiasis the symptoms are recurrent and malabsorption and debilitation may occur.

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  • Page last reviewed November 29, 2013
  • Page last updated November 29, 2013
  • Content source: Global Health - Division of Parasitic Diseases and Malaria
  • Notice: Linking to a non-federal site does not constitute an endorsement by HHS, CDC or any of its employees of the sponsors or the information and products presented on the site.
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