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Worldwide, with higher incidence of amebiasis in developing
countries. In industrialized countries, risk groups include male
homosexuals, travelers and recent immigrants, and institutionalized
populations |
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E.histolytica
trophozoite: the cytoplasm contains fine granular matter;
erythrocytes and bacteria are occasionally seen.
Non invasive trophozoites measure 15-20 µm in diameter.
Differences from typical morphology are possible and frequent |
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E.histolytica
trophozoite: the nucleus has a peripheral uniformly distributed
chromatin and a central located small karyosome.
Specific identification of the parasite is possible with permanent
stains.
(Trichrome stain). |
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Quiste de Entamoeba histolytica
Esféricos miden entre 10 a 20 mm. Tienen desde 1 a 4 núcleos, los que
presentan las mismas características descritas para el núcleo del
trofozoíto. En los quistes inmaduros o prequistes se observan con más
frecuencia cuerpos cromatoidales en forma de barra con los extremos
redondeados y masas de glicógeno |
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Trofozoíto de Entamoeba histolytica
Miden entre 15 a 60 mm. Tienen un núcleo con cromatina periférica
formada por numerosos gránulos uniformemente distribuidos y situados
en la superficie interna de la membrana nuclear. El cariosoma es
puntiforme y central. El citoplasma presenta finas granulaciones ; en
ocasiones pueden encontrarse hematíes fagocitados. |
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Amebiasis is transmitted by fecal contamination
of drinking water and foods, but also by direct contact with dirty
hands or objects as well as by sexual contact.
- Entamoeba
histolytica has a worldwide
distribution with a higher incidence in developing countries.
- In developed
countries, groups at increase risk of disease include male
homosexuals, travelers, recent immigrants and institutionalized
populations.
- Entamoeba
histolytica has a
human reservoir only.
- Not all strains are
pathogenic. Trophozoites cultured from cysts meeting the criteria
for E. histolytica were not always pathogenic. Enzyme
electrophoresis revealed that there were different
zymodemes. Only a few zymodemes are
associated with pathogenicity (E. histolytica). The others
were morphologically indistinguishable but harmless commensals (E.
dispar).
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One of the difficulties in diagnostic parasitology is distinguishing
parasitic organisms from other elements in feces and other body fluids.
The most difficult specimen to differentiate parasites from artifacts in
is feces. Fecal specimens consist of many components such as:
- food residue
- products of
digestion
- epithelial
cells, leucocytes, erythrocytes
- mucus
- microorganisms
such as yeast and bacteria
Due to the ratio of fecal debris to parasites, it is not surprising that
these artifacts may be incorrectly identified as trophozoites, eggs, cysts
and larvae.
The goal of this site is not to replace practical training of staff in
this specialized area. This site is a supplementary source of reference
material that is available to help advanced and beginner microscopists
minimize identification errors by being better able to differentiate "facts
from artifacts."
Fecal artifacts illustrated are:
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Human
cells/cell derived materials
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Charcot-Leyden
crystals
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Macrophages
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Polymorphonuclear
leucocytes
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Red blood cells
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Non-human elements
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Algae
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Fungal conidia
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Mushroom spores
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Plant cells
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Root hairs
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Pollen grains
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Spore
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Vegetable spiral
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Yeast cell
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E.histolytica:
cysts with 4 visible nuclei.
One cyst contains also elliptical chromidial body.
The mature quadrinucleate cyst measures 8-15 µm in diameter. |
E.histolytica:
trophozoite of E.histolytica forma minuta. 10-20 µm in diameter.
Stained fecal film. Wheatley modification of Gomori‘s trichrome
technique.
Objective 100 X |
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E.histolytica:
trophozoite of E.histolytica forma magna (dysenterica).
10-20 µm in diameter, with ingested erythrocytes in the endoplasm.
Stained fecal film. Wheatley modification of Gomori‘s trichrome
technique.
Objective 100 X |
LINKS
Life cycle of
Entamoeba histolytica: the disease has a world-wide
distribution
with a higher prevalence in tropical and subtropical countries.
10% of the world population carries the protozoa. |
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A
website to assist microscopists in the differentiation of clinically
important parasites from artifact material regularly seen in fecal
samples and specimens from other body sites.
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Entamoeba histolytica
has a worldwide distribution with a higher
incidence in developing countries. |
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