Giardia duodenalis

Giardia duodenalis
Giardia lamblia cell, SEM
Scientific classification
Domain:	Eukaryota
Phylum:	Metamonada
Order:	Diplomonadida
Family:	Hexamitidae
Genus:	Giardia
Species:	G. duodenalis
Binomial name
Giardia duodenalis Stiles, 1902
Synonyms
Cercomonas intestinalis Lambl, 1859 Lamblia intestinalis Blanchard, 1888 Giardia lamblia (Lambl, 1859) Kofoid & Christiansen, 1915 Giardia intestinalis Kulda & Nohýnková, 1995

Giardia duodenalis, also known as Giardia intestinalis and Giardia lamblia, is a flagellated parasitic protozoan microorganism of the genus Giardia that colonizes the small intestine, causing a diarrheal condition known as giardiasis.^[1][2][3] The parasite attaches to the intestinal epithelium by an adhesive disc or sucker, and reproduces via binary fission.^[4] Giardiasis does not spread to other parts of the gastrointestinal tract, but remains confined to the lumen of the small intestine.^[5] The microorganism has an outer membrane that makes it possible to survive even when outside of its host, and which can render it tolerant to certain disinfectants. Giardia trophozoites are anaerobic, and absorb their nutrients from the intestinal lumen. If the organism is stained, its characteristic pattern resembles the familiar "smiley face" symbol.^[6]

Chief pathways of human infection include ingestion of untreated drinking water (which is the most common method of transmission for this parasite),^[3] food, soil contaminated with human feces, and sewage, a phenomenon particularly common in many developing countries.^[7][3] Contamination of natural waters also occurs in watersheds where intensive grazing occurs.

Giardia infections occur worldwide. It is the most commonly identified intestinal parasite among children in day-care centers, hikers, immunocompromised adults and their family members in the United States and Canada. About 20,000 cases per year in the United States are reported.^[8]