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Entamoeba histolytica
Entamoeba histolytica cyst
Scientific classification
Domain: Eukaryota
Phylum: Amoebozoa
Class: Archamoebae
Order: Amoebida
Genus: Entamoeba
Species: E. histolytica
Life-cycle of the Entamoeba histolytica

Entamoeba histolytica is an anaerobic parasitic protozoan, part of the genus Entamoeba.[1] Predominantly infecting humans and other primates, E. histolytica is estimated to infect about 50 million people worldwide. Many older textbooks state that 10% of the world population is infected, but these figures predate the recognition that at least 90% of these infections were due to a second species, E. dispar.[2] Mammals such as dogs and cats can become infected transiently, but are not thought to contribute significantly to transmission.



The active (trophozoite) stage exists only in the host and in fresh loose faeces; 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.[3] 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 was also found to be transmitted through anal-oral sex. The research have shown that HIV-infected gay men were at greater risk of getting infected than healthy population and than seropositive heterosexuals.[4]


E. histolytica, as its name suggests (histolytic = tissue destroying), is pathogenic; infection can lead to amoebic dysentery or amoebic liver abscess.[1] Symptoms can include fulminating dysentery, bloody diarrhea, weight loss, fatigue, abdominal pain, and amoeboma. 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.


The genome data of E. histolytica have been re-assembled and re-annotated, incorporating significant structural and functional modifications to existing gene models. The 20 million basepair genome assembly contains 8,160 predicted genes; known and novel transposable elements have been mapped and characterized, functional assignments have been revised and updated, and additional information has been incorporated, including metabolic pathways, Gene Ontology assignments, curation of transporters, and generation of gene families.[5]

Pathogen Interaction

E. histolytica mediates the virulence of viruses and is itself a host for viruses.

For example, as mentioned AIDS accentuates the damage and pathogenicity of E. histolytica[6]. On the other hand, cells infected with HIV are often consumed by E. histolytica. Infective HIV remains viable within the amoeba, although fortunately there has been no proof of human reinfection from amoeba carrying this virus.[7].

A burst of research on viruses of E. histolytica stem from a series of papers published by Diamond et al. from 1972 to 1979. In 1972, they hypothesized two separate polyhedral and filamentous viral strains within E. histolytica that caused cell lysis. Perhaps the most novel observation was that two kinds of viral strains existed, and that within one type of amoeba (dubbed HB-301) the polyhedral strain had no detrimental effect but led to cell lysis in other (dubbed HK-9) strains. Although Mattern et al. attempted to explore the possibility that these protozoal viruses could function like bacteriophages, they find no significant changes in Entamoeba histolytica virulence when infected by viruses. Unfortunately no newer research seems to have been conducted on this species since.[8].


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.

Genus and Species Entamoeba histolytica
Etiologic Agent of: Amoebiasis; Amoebic dysentery; Extraintestinal Amoebiasis, usually Amoebic Liver Abscess = “anchovy sauce”); Amoeba Cutis; Amoebic Lung Abscess (“liver-colored sputum”)
Infective stage Quadrinucleated cyst (having 4 nuclei)
Definitive Host Human
Portal of Entry Mouth
Mode of Transmission Ingestion of mature cyst through contaminated food or water
Habitat Colon and Cecum
Pathogenic Stage Trophozoite
Locomotive apparatus Pseudopodia (“False Foot”)
Motility Active, Progressive and Directional
Nucleus 'Ring and dot' appearance: peripheral chromatin and central karyosome
Mode of Reproduction Binary Fission
Pathogenesis Lytic necrosis (it looks like “flask-shaped” holes in Gastrointestinal tract sections (GIT)
Type of Encystment Protective and Reproductive
Lab Diagnosis 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; PCR for species identification. Sometimes only the use of a fixative (formalin) is effective in detecting cysts. Culture: From faecal samples - Robinson's medium, Jones' medium
Treatment Metronidazole for the invasive trophozoites PLUS a lumenal amoebicide for those still in the intestine. Paromomycin (Humatin) is the lumenal drug of choice, since Diloxanide furoate (Furamide) is not commercially available in the USA or Canada (only being available from the Centers for Disease Control and Prevention). A direct comparison of efficacy showed that Paromomycin had a higher cure rate [9]. Paromomycin(Humatin)should be used with caution in patients with colitis as it is both nephrotoxic and ototoxic. Absorption through the damaged wall of the intestinal tract can result in permanent hearing loss and kidney damage. Recommended dosage: Metronidazole 750mg tid orally, for 5 to 10 days FOLLOWED BY Paromomycin 30mg/kg/day orally in 3 equal doses for 5 to 10 days or Diloxanide furoate 500mg tid orally for 10 days, to eradicate lumenal amoebae and prevent relapse [10].
Trophozoite Stage
Pathognomonic/Diagnostic Feature Ingested RBC; distinctive nucleus
Cyst Stage
Chromatoidal Body 'Cigar' shaped bodies (made up of crystalline ribosomes)
Number of Nuclei 1 in early stages, 4 when mature
Pathognomonic/Diagnostic Feature 'Ring and dot' nucleus and chromatoid bodies

Additional images

See also


  1. ^ a b Ryan KJ, Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed. ed.). McGraw Hill. pp. 733–8. ISBN 0838585299. 
  2. ^ "Amoebiasis". Wkly. Epidemiol. Rec. 72 (14): 97–9. April 1997. PMID 9100475. 
  3. ^ Waterborne Pathogens. American Water Works Association. 2006-06. ISBN 9781583214039. 
  4. ^ Institute of Tropical Medicine Antwerp (2009, November 26). "New disease among HIV-infected gay men". ScienceDaily. 
  5. ^ Caler, E and Lorenzi, H (2010). "Entamoeba histolytica: Genome Status and Web Resources". Anaerobic Parasitic Protozoa: Genomics and Molecular Biology. Caister Academic Press. ISBN 978-1-904455-61-5. 
  6. ^ Hung CC, Deng HY, Hsiao WH, Hsieh SM, Hsiao CF, Chen MY, Chang SC, Su KE. (Feb 2005). "Invasive amebiasis as an emerging parasitic disease in patients with human immunodeficiency virus type 1 infection in Taiwan.". Arch Intern Med. 165 (4): pp. 409 - 415. 
  7. ^ Brown M, Reed S, Levy JA, Busch M, McKerrow JH. (Jan 1991). "Detection of HIV-1 in Entamoeba histolytica without evidence of transmission to human cells.". AIDS. 5 (1): pp. 93-6. 
  8. ^ Diamond LS, Mattern CF, Bartgis IL (Feb 1972). "Viruses of Entamoeba histolytica. I. Identification of transmissible virus-like agents.". J Virol. 9 (2): pp. 326-41. 
  9. ^ Blessmann J, Tannich E (October 2002). "Treatment of asymptomatic intestinal Entamoeba histolytica infection". N. Engl. J. Med. 347 (17): 1384. doi:10.1056/NEJM200210243471722. PMID 12397207. 
  10. ^ Stanley SL (March 2003). "Amoebiasis". Lancet 361 (9362): 1025–34. doi:10.1016/S0140-6736(03)12830-9. PMID 12660071. 

External links

Entamoeba histolytica article] from the US Food and Drug Administration's Bad Bug Book


Up to date as of January 23, 2010

From Wikispecies

Entamoeba histolytica


Main Page
Cladus: Eukaryota
Supergroup: Unikonta
Phylum: Amoebozoa
Classis: Conosea
Infraphylum: Archamoebae
Classis: Archamoeba
Ordo: Pelobiontida
Familia: Entamoebidae
Genus: Entamoeba
Species: Entamoeba histolytica


Entamoeba histolytica Schaudinn, 1903


Simple English

Entamoeba histolytica
Scientific classification
Domain: Eukaryota
Phylum: Amoebozoa
Class: Archamoebae
Order: Amoebida
Genus: Entamoeba
Species: E. histolytica

Entamoeba histolytica is an parasitic protozoan, part of the genus Entamoeba. It infects mainly humans and other primates. Also known as E. histolytica, it is estimated to infect about 50 million people worldwide.

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