Entamoeba histolytica
334768
225472962
2008-07-13T21:45:00Z
Blechnic
6713598
{{Taxobox
| name = ''Entamoeba histolytica''
| image = Entamoeba_histolytica_01.jpg
| image_width = 240px
| image_caption = ''Entamoeba histolytica'' [[cyst]]
| domain = [[Eukaryota]]
| kingdom = [[Protista]]
| phylum = [[Amoebozoa]]
| classis = [[Archamoebae]]
| genus = ''[[Entamoeba]]''
| species = '''''E. histolytica'''''
}}
[[Image:Entamoeba histolytica life cycle-en.svg|thumb|right|250px|Life-cycle of the ''Entamoeba histolytica'']]
''For the infection and disease caused by this parasite, refer to [[Amoebiasis]].''
'''''Entamoeba histolytica''''' is an [[anaerobic organism|anaerobic]] parasitic [[protozoa]]n, part of the [[genus]] ''[[Entamoeba]]''. It infects predominantly humans and other primates. It is estimated that about 50 million people are infected with the parasite worldwide. Diverse mammals such as dogs and cats can become infected but are not thought to contribute significantly to transmission. The active ([[trophozoite]]) stage exists only in the host and in fresh loose feces; [[cyst]]s 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.<ref>{{cite book|last = American Water Works Association|title=Waterborne Pathogens|date=2006-06|publisher=[[American Water Works Association]]|isbn=9781583214039}}</ref> 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.
''E. histolytica'', as its name suggests (''histo''–''lytic'' = tissue destroying), causes disease; infection can lead to [[Dysentery|amoebic dysentery]] or amoebic [[liver abscess]]. Symptoms can include fulminating dysentery, diarrhea, weight loss, fatigue, abdominal pain, and [[ameboma]]s. The amoeba can actually 'bore' into the intestinal wall, causing [[lesion]]s 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 cell]]s are sometimes seen in the amoeba cell cytoplasm.
It can be diagnosed by [[feces|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 [[Radioimmunoassay|RIA]] can also be used.
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{| class="wikitable" border="2" cellpadding="5" cellspacing="0" align="center"
|-
|width="200pt" align="center"| '''Genus and Species'''
|width="400pt" align="center"| ''Entamoeba histolytica''
|-
|width="200pt" align="center"| '''Etiologic Agent of:'''
|width="400pt" align="center"| [[Amoebiasis]]; [[Amoebic dysentery]]; Extraintestinal Amoebiasis, usually Amoebic Liver Abscess = “anchovy sauce”); [[Amoeba Cutis]]; [[Amoebic Lung Abscess]] (“liver-colored sputum”)
|-
|width="200pt" align="center"| '''Infective stage'''
|width="400pt" align="center"| Cyst
|-
|width="200pt" align="center"| '''Definitive Host'''
|width="400pt" align="center"| Human
|-
|width="200pt" align="center"| '''Portal of Entry'''
|width="400pt" align="center"| Mouth
|-
|width="200pt" align="center"| '''Mode of Transmission'''
|width="400pt" align="center"| Ingestion of mature cyst through contaminated food or water
|-
|width="200pt" align="center"| '''Habitat'''
|width="400pt" align="center"| Colon and Cecum
|-
|width="200pt" align="center"| '''Pathogenic Stage'''
|width="400pt" align="center"| [[Trophozoite]]
|-
|width="200pt" align="center"| '''Locomotive apparatus'''
|width="400pt" align="center"| Pseudopodia (“False Foot”)
|-
|width="200pt" align="center"| '''Motility'''
|width="400pt" align="center"| Active, Progressive and Directional
|-
|width="200pt" align="center"| '''Nucleus'''
|width="400pt" align="center"| 'Ring and dot' appearance: peripheral chromatin and central karyosome
|-
|width="200pt" align="center"| '''Mode of Reproduction'''
|width="400pt" align="center"| Binary Fission
|-
|width="200pt" align="center"| '''Pathogenesis'''
|width="400pt" align="center"| Lytic necrosis (it looks like “flask-shaped” holes in Gastrointestinal tract sections (GIT)
|-
|width="200pt" align="center"| '''Type of Encystment'''
|width="400pt" align="center"| Protective and Reproductive
|-
|width="200pt" align="center"| '''Lab Diagnosis'''
|width="400pt" align="center"| Most common is Direct Fecal Smear (DFS) and staining (but does not allow identification to species level); [[Enzyme immunoassay]] (EIA); [[Indirect Hemagglutination]] (IHA); Antigen detection – monoclonal antibody; [[polymerase chain reaction|PCR]] for species identification. Culture: From faecal samples - Robinson's medium, Jones' medium
|-
|width="200pt" align="center"| '''Treatment'''
|width="400pt" align="center"| [[Metronidazole]] for the invasive trophozoites PLUS a lumenal amoebicide for those still in the intestine ([[Paromomycin]] is the most widely used)
|-
{| border="0"
|colspan="2" align="center" bgcolor="khaki"| '''Trophozoite Stage'''
|-
|width="200pt" align="center"| '''Pathognomonic/Diagnostic Feature'''
|width="400pt" align="center"| Ingested RBC; distinctive nucleus
|-
{| border="0"
|colspan="2" align="center" bgcolor="khaki"| '''Cyst Stage'''
|-
|width="200pt" align="center"| '''Chromatoidal Body'''
|width="400pt" align="center"| 'Cigar' shaped bodies (made up of crystalline ribosomes)
|-
|width="200pt" align="center"| '''Number of Nuclei'''
|width="400pt" align="center"| 1 in early stages, 4 when mature
|-
|width="200pt" align="center"| '''Pathognomonic/Diagnostic Feature'''
|width="400pt" align="center"| 'Ring and dot' nucleus and chromatoid bodies
|-
|}
|}
|}
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==See also==
* [[List of parasites (human)]]
==References==
{{reflist}}
== External links ==
* [[Centers for Disease Control and Prevention|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]
* <small>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.</small>
[[Category:Amoebozoa]]
[[Category:Parasites]]
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