Entamoeba histolytica
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 Entamoeba histolytica cyst
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For the parasitical infection, refer to Amoebiasis.
Entamoeba histolytica is an anaerobic parasitic eukaryote protozoan, part of the genus Entamoeba. It infects predominantly humans and other primates. Diverse mammals such as dogs and cats can become infected but usually do not shed cysts (the environmental survival form of the organism) with their feces, thus do not contribute significantly to transmission. The active (trophozoite) stage exists only in the host and in fresh feces; cysts survive outside the host in water and soils and on foods, especially under moist conditions on the latter. When swallowed they cause infections by excysting (to the trophozoite stage) in the digestive tract.
Entamoeba histolytica, as its name suggests, can actually bore through the enteric walls (histolysis = destroying tissue) and reach the blood stream. From there, it can reach different vital organs of the human body, like the liver, lungs, brain, eyes etc. A typical effect is a liver abscess caused by such migrating Entamoeba histolytica, which can be fatal. Ingested red blood cells are sometimes seen in the cytoplasm.
Entamoeba histolytica infection can lead to amebiasis or amebic dysentery. Symptoms include fulminating dysentery, diarrhea, weight loss, fatigue, abdominal pain, and amebomas.
It can be diagnosed by stool samples. Trophozoites should 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 liver = “anchovy sauce”); Amoeba Cutis; Amoebic Lung Abscess (“liver-colored sputum) |
| Infective stage | Cyst |
| Definitive Host | Man |
| Portal of Entry | Mouth |
| Mode of Transmission | Ingestion of mature cyst through contaminated food or water |
| Habitat | Cecum |
| Pathogenic Stage | Trophozoite |
| Locomotive apparatus | Pseudopodia (“finger-like”) |
| Motility | Active, Progressive and Directional |
| Nuclear Karyosome | Central, "Bull's Eye" |
| 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); Enzymeimmunoassay (EIA); Indirect Hemagglutination (IHA); Antigen detection – monoclonal Antibody; Polymerase Chain Reaction PCR for comparative analysis. Culture: Triple N media |
| Treatment | Metronidazole |
| Trophozoite Stage | |
| Pathognomonic/Diagnostic Feature | Ingested RBC; Bull’s eye Karyosome |
| Cystic Stage | |
| Chromatoidal Body | Ingested RBC; Bull’s eye Karyosome |
| Number of Nucleus | 1 to 4 |
| Number of Nuclear Division | 2 |
| Pathognomonic/Diagnostic Feature | Bull’s eye karyosome |
[edit] External links
- Public domain Entamoeba histolytica article from the Bad Bug Book, from which the original version of this article was adapted
- CDC DPDx Parasitology Diagnostic Web Site
