Entamoeba histolytica

Taxobox
name = "Entamoeba histolytica"

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image_width = 240px
image_caption = "Entamoeba histolytica" cyst
domain = Eukaryota
kingdom = Protista
phylum = Amoebozoa
classis = Archamoebae
genus = "Entamoeba"
species = "E. histolytica""For the infection and disease caused by this parasite, refer to Amoebiasis."

"Entamoeba histolytica" is an anaerobic parasitic protozoan, part of the genus "Entamoeba".cite book | author = Ryan KJ, Ray CG (editors) | title = Sherris Medical Microbiology | edition = 4th ed. | pages=pp. 733-8 | publisher = McGraw Hill | year = 2004 | isbn = 0838585299] Predominantly infecting humans and other primates. "E. histolytica" is estimated to infect about 50 million people worldwide. Mammals such as dogs and cats can become infected transiently, but are not thought to contribute significantly to transmission.

Transmission

The active (trophozoite) stage exists only in the host and in fresh loose feces; cysts survive outside the host in water, soils and on foods, especially under moist conditions on the latter. The cysts are readily killed by heat and by freezing temperatures, and survive for only a few months outside of the host. [cite book|last = American Water Works Association|title=Waterborne Pathogens|date=2006-06|publisher=American Water Works Association|isbn=9781583214039] When cysts are swallowed they cause infections by excysting (releasing the trophozoite stage) in the digestive tract. The trophozoite stage is readily killed in the environment and cannot survive passage through the acidic stomach to cause infection.

Pathogenesis

"E. histolytica", as its name suggests ("histo"–"lytic" = tissue destroying), is pathogenic; infection can lead to amoebic dysentery or amoebic liver abscess. Symptoms can include fulminating dysentery, diarrhea, weight loss, fatigue, abdominal pain, and amebomas. The amoeba can actually 'bore' into the intestinal wall, causing lesions and intestinal symptoms, and it may reach the blood stream. From there, it can reach different vital organs of the human body, usually the liver, but sometimes the lungs, brain, spleen, etc. A common outcome of this invasion of tissues is a liver abscess, which can be fatal if untreated. Ingested red blood cells are sometimes seen in the amoeba cell cytoplasm.

Diagnosis

It can be diagnosed by stool samples but it is important to note that certain other species are impossible to distinguish by microscopy alone. Trophozoites may be seen in a fresh fecal smear and cysts in an ordinary stool sample. ELISA or RIA can also be used.

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See also

* List of parasites (human)

References

External links

* CDC [http://www.dpd.cdc.gov/dpdx/ "DPDx Parasitology Diagnostic Web Site"]
* LSHTM [http://homepages.lshtm.ac.uk/entamoeba/ "Entamoeba Homepage"]
* [http://pathema.jcvi.org/cgi-bin/Entamoeba/PathemaHomePage.cgi Pathema-"Entamoeba" Resource]
* Public domain [http://vm.cfsan.fda.gov/~mow/chap23.html "Entamoeba histolytica" article] from the Bad Bug Book, from which the original version of this article was adapted.