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Questions and Answers
What is the main characteristic of Sarcodina (Amoebae) in the phylum Sarcomastigophora?
What is the main characteristic of Sarcodina (Amoebae) in the phylum Sarcomastigophora?
How does infection by E.histolytica usually occur?
How does infection by E.histolytica usually occur?
Which form of Entamoeba histolytica exists in 10-60 µm size with unidirectional motility and a single pseudopodium?
Which form of Entamoeba histolytica exists in 10-60 µm size with unidirectional motility and a single pseudopodium?
Where do trophozoites of E.histolytica reside?
Where do trophozoites of E.histolytica reside?
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Which phylum contains Ciliates under the classification of protozoa?
Which phylum contains Ciliates under the classification of protozoa?
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How do trophozoites of E.histolytica multiply?
How do trophozoites of E.histolytica multiply?
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What is the fate of trophozoites passed in the stool?
What is the fate of trophozoites passed in the stool?
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What happens during encystation in the intestinal lumen?
What happens during encystation in the intestinal lumen?
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What is a characteristic of E.histolytica and E.dispar?
What is a characteristic of E.histolytica and E.dispar?
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How do viable cysts in the external environment meet their end?
How do viable cysts in the external environment meet their end?
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What is the primary route for trophozoites to reach extraintestinal sites?
What is the primary route for trophozoites to reach extraintestinal sites?
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What distinguishes noninvasive infection from invasive infection in terms of species?
What distinguishes noninvasive infection from invasive infection in terms of species?
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What process occurs when the amoeba becomes active, ruptures the cyst membrane, and starts to multiply by binary fission?
What process occurs when the amoeba becomes active, ruptures the cyst membrane, and starts to multiply by binary fission?
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What is the common manifestation of intestinal amoebiasis caused by E.histolytica?
What is the common manifestation of intestinal amoebiasis caused by E.histolytica?
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What is the extraintestinal manifestation that may develop in about 5-10% of individuals with intestinal amoebiasis?
What is the extraintestinal manifestation that may develop in about 5-10% of individuals with intestinal amoebiasis?
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What are the factors that determine the pathogenicity of E.histolytica?
What are the factors that determine the pathogenicity of E.histolytica?
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What is the term used to describe pseudotumoral lesions associated with necrosis, inflammation, and edema caused by E.histolytica?
What is the term used to describe pseudotumoral lesions associated with necrosis, inflammation, and edema caused by E.histolytica?
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What might happen when E.histolytica enters general circulation from liver abscesses?
What might happen when E.histolytica enters general circulation from liver abscesses?
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What is the common method for diagnosing Entamoeba histolytica?
What is the common method for diagnosing Entamoeba histolytica?
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What is the differentiation method between Entamoeba histolytica and Entamoeba dispar based on?
What is the differentiation method between Entamoeba histolytica and Entamoeba dispar based on?
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What is the drug of choice for asymptomatic Entamoeba histolytica infections?
What is the drug of choice for asymptomatic Entamoeba histolytica infections?
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What laboratory test shows moderate leukocytosis in invasive amoebiasis?
What laboratory test shows moderate leukocytosis in invasive amoebiasis?
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Which method can be used to identify trophozoites obtained during colonoscopy or surgery?
Which method can be used to identify trophozoites obtained during colonoscopy or surgery?
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What is the immediate treatment to follow after using metronidazole or tinidazole for symptomatic Entamoeba histolytica infections?
What is the immediate treatment to follow after using metronidazole or tinidazole for symptomatic Entamoeba histolytica infections?
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Which amoeba can cause an acute and fulminating meningoencephalitis in immunocompetent children and young adults?
Which amoeba can cause an acute and fulminating meningoencephalitis in immunocompetent children and young adults?
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How is Entamoeba dispar differentiated from E.histolytica?
How is Entamoeba dispar differentiated from E.histolytica?
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Which amoeba has mature cysts with 8 nuclei and an eccentric endosome?
Which amoeba has mature cysts with 8 nuclei and an eccentric endosome?
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What distinguishes Naegleria fowleri from other amoebae?
What distinguishes Naegleria fowleri from other amoebae?
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Which amoeba is very small (6-15um) with a large, eccentric endosome and thin nuclear envelope?
Which amoeba is very small (6-15um) with a large, eccentric endosome and thin nuclear envelope?
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In which stage can Naegleria fowleri be seen as either an amoeboid or temporary flagellate?
In which stage can Naegleria fowleri be seen as either an amoeboid or temporary flagellate?
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Study Notes
Protozoa
- Single-celled animals that perform all necessary functions of life, with most being free-living.
- Classified under four phyla: Sarcomastigophora, Apicomplexa, Ciliophora, and Microspora.
Sarcomastigophora Phylum
- Subdivided into two subphyla: Sarcodina and Mastigophora.
- Sarcodina (Amoebae): Use pseudopodia for locomotion and feeding.
Entamoeba Histolytica
- A type of amoeba that is medically important.
- Exists in three forms: trophozoite, precyst, and cyst.
- Trophozoites:
- 10-60 µm in size.
- Have unidirectional motility and a single pseudopodium.
- Ingest erythrocytes.
- Have granular cytoplasm, a small central karyosome, and beaded chromatin.
- Reside in the mucosa and submucosa of the large intestine of humans.
- Life cycle:
- Infection occurs through ingesting mature cysts in contaminated food, water, or hands.
- Excystation occurs in the small intestine, releasing trophozoites that migrate to the large intestine.
- Trophozoites multiply by binary fission and produce cysts.
- Both stages are passed in the feces.
Encystation
- Occurs in the intestinal lumen.
- Chromatin is concentrated into bars or grape-like clusters (chromatoidal bodies) in the cytoplasm of the cyst.
- The nucleus of the cyst divides into two, then each daughter nucleus divides again, resulting in a mature cyst with four nuclei.
- Diffuse glycogen becomes concentrated in a mass with a hazy margin.
Excystation
- Occurs only after a mature cyst has been ingested and reaches a suitable level of the intestine.
- The amoeba becomes active, ruptures the cyst membrane, and starts to multiply by binary fission and colonization inside the host's digestive tract.
Pathogenesis
- Intestinal amoebiasis:
- Amoeba invades colonic mucosa, producing flask-shaped ulcers and profuse bloody diarrhea (amoebic dysentery).
- Ulcers may be deep or superficial.
- Extraintestinal amoebiasis:
- Amoeba multiply in the liver, leading to cytolytic action and small abscesses that merge to form large liver abscesses.
- Abscesses can grow in various directions, entering the general circulation and involving the lungs, brain, spleen, skin, etc.
Laboratory Diagnosis
- Diagnosis involves differentiation from other intestinal non-pathogenic amoebae.
- Microscopic identification of cysts and trophozoites in the stool is the common method for diagnosing E. histolytica.
- Other methods include blood examination, serological tests, histology, and molecular methods.
Treatment
- Asymptomatic infections: paromomycin or iodoquinol.
- Symptomatic intestinal or extraintestinal infections: metronidazole or tinidazole, followed by paromomycin or iodoquinol.
- Failure of metronidazole therapy may require surgical intervention.
Non-Pathogenic Amoebae
- Entamoeba dispar: Morphologically identical to E. histolytica, but can be differentiated by isoenzymatic, immunologic, or molecular analyses.
- Entamoeba hartmanni: Smaller in size than E. histolytica.
- Entamoeba coli: Distinguished from E. histolytica by having an eccentric endosome and mature cysts with 8 nuclei.
- Endolimax nana: Small amoeba with a large, eccentric endosome and thin nuclear envelope.
- Iodamoeba butschlii: Trophozoite and cyst have one nucleus with a large endosome, and the cyst contains a large glycogen vacuole.
Pathogenic and Opportunistic Free-Living Amoebae
- Naegleria fowleri: Causes acute and fulminating meningoencephalitis in immunocompetent children and young adults.
- Found in warm freshwater and soil near industrial plants, and in unchlorinated swimming pools.
- Can be seen in either an amoeboid or temporary flagellate stage.
- N. fowleri is inhaled through the nose, entering the nasal and olfactory nerve tissue and travelling to the brain.
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Description
Test your knowledge on the life cycle and pathogenesis of Entamoeba histolytica. Questions cover the process of excystation, colonization inside the host's digestive tract, and the pathogenesis of intestinal amoebiasis.
