البوم ل Entamoeba histolytica

Entamoeba
histolytica

E. histolytica/E. dispar
cysts in concentrated wet mounts.

Mature Entamoeba
histolytica/Entamoeba dispar cysts have 4 nuclei that
characteristically have centrally-located karyosomes
and fine, uniformly distributed peripheral chromatin. Cysts usually
measure 12 to 15 µm.


A	B

A, B: Cysts of
E.
histolytica/E. dispar in an unstained concentrated wet mount
of stool. Notice the chromatoid bodies with blunt, rounded ends
(arrows).


C	D

C, D: Cysts of
E.
histolytica/E. dispar in a concentrated wet mount stained with iodine.
Notice the chromatoid body with blunt, rounded ends in Figure D
(arrow).

E. histolytica/E. dispar
cysts stained with trichrome.

Mature Entamoeba
histolytica/Entamoeba dispar cysts have 4 nuclei that
characteristically have centrally-located karyosomes
and fine, uniformly distributed peripheral chromatin. Cysts usually
measure 12 to 15 µm.


A	B

A: Cyst of E.
histolytica/E. dispar stained with trichrome. Note the chromatoid body with blunt ends (red arrow).

B: Cyst of
E.
histolytica/E. dispar stained with trichrome.


C	D

C,
D: Cysts of E.
histolytica/E. dispar stained with trichrome.
Two to three nuclei are visible in the focal plane (black arrows), and the cysts
contain chromatoid bodies with typically blunted ends (red arrows).
The chromatoid body in C is particularly well demonstrated.

Life cycle of
E. histolytica.

البوم ل Entamoeba histolytica Amebiasis_LifeCycle

Cysts and
trophozoites are passed in feces
.
Cysts are typically found in formed stool, whereas trophozoites are
typically found in diarrheal stool. Infection by Entamoeba histolytica occurs by ingestion of mature cysts
in fecally contaminated food, water, or hands.
Excystation
occurs in the small intestine and trophozoites
are released, which migrate to the large intestine.
The trophozoites multiply by binary fission and produce cysts
,
and both stages are passed in the feces
.

Because of the protection conferred by their walls, the cysts can
survive days to weeks in the external environment and are responsible
for transmission. Trophozoites passed in the stool are rapidly
destroyed once outside the body, and if ingested would not survive
exposure to the gastric environment. In many cases, the trophozoites
remain confined to the intestinal lumen (: noninvasive infection) of individuals who are asymptomatic carriers,
passing cysts in their stool. In some patients the trophozoites invade the intestinal mucosa (: intestinal disease), or, through the bloodstream, extraintestinal sites such as the liver, brain, and lungs (: extraintestinal disease), with resultant pathologic manifestations.
It has been established that the invasive and noninvasive forms represent
two separate species, respectively E. histolytica and E. dispar. These two species are morphologically
indistinguishable unless E. histolytica is observed with ingested red
blood cells (erythrophagocystosis). Transmission can also occur through
exposure to fecal matter during sexual contact (in which case not only cysts, but also trophozoites could prove infective).