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Amoeboid Protozoa, amoebiasis
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By putri wahyuni siburian
1. Unicellular protozoa move and
feed by means of cytoplasmic
projections termed pseudopodia
2. Amoeboid protozoa are
characterised on the form and
structure of their pseudopods
3. Common in soils and aquatic
4. Entamoeba are both pathogens
of and commensals in animals
5. Dictyostelium (slime mould) is
a amoeba with a complex life
cycle involving unicellular and
multicellular phases
Amoeboid Protozoa
Amoeba classification
1. Pathogenic : Intestinal amoeba (Entamoeba histolytica).
2. non pathogenic : Mouth amoeba (Entamoeba Gingivalis)
Intestinal amoeba (Entamoeba coli, endolimax nana,iodamoeba
butschlii and dientamoeba fragilis)
Entamoeba histolytica
Entamoeba histolytica is a protozoan parasite that causes amebic dysentery and liver
abscess. The disease is common in tropical regions of the world where hygiene and
sanitation is often approximate.
Cyst of E. histolytica/E.
dispar stained with
trichrome. Note the
chromatoid body with blunt
ends (red arrow).
Trophozoites of E. histolytica
with ingested erythrocytes
stained with trichrome. The
ingested erythrocytes appear as
dark inclusions. The parasite
above show nuclei that have the
typical small, centrally located
karyosome, and thin, uniform
peripheral chromatin.
Entamoeba histolytica
trophozoites in colon
tissue stained with H&E.
Amoebiasis is an infection caused by Entamoeba histolytica with or without
symptoms (WHO 1969). Synonyms include entamoebiasis, amoebiosis,
amoebic dysentery or bloody flux. Entamoeba dispar is a harmless commensal,
which is indistinguishable from E. histolytica. The other members of the group
infecting humans are E. moshkovskii,E. hartmannii,E. gingivalis,Endolimax
nana and Iodamoeba butschlii.
Life Cycle of Entamoeba histolytica
1. Trophozoite
10-60 X15-30 m average (20-25
Cytoplasm is clearly differentiated
oEctoplasm: is clear with well
developed pseudopodia.
oEndoplasm: dense & fine granular
Nucleus: spherical containing
central karyosome & peripheral
evenly distributed small chromatin
Food vacuoles: contain leucocytes-
bacteria-may be RBCs.
2. Precyst stage
10-60 X15-30 m average (15-20 m)
Round or oval with a blunt
Absent cyst wall
Single nucleus present.
3. Cyst
wall, 0.5 mikrometer chromatoid
mature infective cyst : four smaller
Habitat : wall & lumen of the colon
Reproduction: binary fission
10-20 m average (15 m)
Four nuclei are present in mature
quadrinucleated cyst
Glycogen mass & chromatoid bodies
are present in immature cysts disappear
in mature ones.
1. Humans are the only known reservoir. Infections are usually acquired from a
chronically ill or asymptomatic cyst passer
2. Transmission usually follows ingestion of food or water contaminated with
human feces. Fecaloral transmission can also occur in the setting of anal
sexual practices or direct rectal inoculation through colonic irrigation devices.
Insects, particularly flies may also act as vectors of cystladen feces
3. Amoebiasis occurs worldwide, but is mostly seen in tropical and developing
countries. Ten percent of world’s population is estimated to be infected by the
parasite (4% in USA) with an estimated annual mortality of 40,00070,000.
However, 90%of those infected are asymptomatic, 1% may develop invasive
or extraintestinal amoebiasis.
4. More prevalent in certain groups (e.g. children, homosexual, prisoners,
orphanages houses, people in mental hospitals .. etc)
5. Cyst passers are the main source of infection.
6. Cysts remain viable in faeces for few days, in water for longer periods.
7. Cysts are killed by dryness, heat (over 55ºC) and by chlorine
Schematic representation of E. histolytica pathogenesis.
Extraintestinal amebiasis.
Clinical syndromes associated with amebiasis
1. Asymptomatic; parasite in lumen and cysts pass in stool.
2. Symptomatic; fever, diarrhea, dysentery, abdominal pain, localized
abdominal tenderness, tenesmus & strain, painful spasm of anal
sphincter, recurrent attacks of dysentery with intervening periods of
constipation, abdominal distension & Flatulence, weight loss and
cachexia, hepatitis or amoebic abscess, lung abscess, brain abscess or
skin abscess.
1. Clinically: Dysentery: painful frequent evacuation of small quantities of stool
containing mucus tinged with blood.
2. Laboratory with direct stool examination: Trophozoites are found in diarrhoeic
stool. Cysts are found in formed stool.
3. Laboratory by doing concentration techniques for cysts.
4. Indirect diagnosis: Serological tests in chronic amoebiasis. Detection of copro-
antigen using monoclonal antibodies.
Coating the well with MAb and add patient’s stool to detect Entamoeba Ag
5. Radiological examination: using barium enema.
6. Sigmoidoscopy: to visualize the ulcer, scrap, aspirate or take biopsy to see the
Diagnosis (intestinal amoebiasis)
Diagnosis (Extraintestinal amoebiasis)
1. Metronidazole, Tinidazole. Very effective in killing amoebas in the wall of the
intestine, in blood and in liver abscesses.
2. Diluxanide furoate. Kills trophozoites and cysts in the lumen of the intestine.
Treatment of Amoebic abscesses by aspiration or open surgical drainage
Treatment of
amebiasis with drug
diloxanide furoate
Luminal agents to treat
cases and as a follow up
treatment after a
Metronidazole or
Treatment of
colitis, dysentery,
extraintestinal infections
Treatment of severe disease such
as necrotic
colitis, perforation of intestinal
wall, rupture of
liver abscess
Consult your doctor if you have travelled to an endemic area
and suspect you may have it
Know the symptoms of amebiasis, when they are present
Obtain treatment promptly if you have been diagnosed with
Trying Medical Treatments
Monitor diarrhea and fluid loss
Trying Surgical Treatments for uncontrollable and debilitating bowel
symptoms such as abdominal pain, diarrhea, and/or constipation
Get your liver treated (via medication or needle drainage) if needed
Using Preventative Measures
Use preventative measures when
travelling to endemic areas
(where the disease is
common). These include:
Safe sexual
Appropriate water treatment
Safe food choices
Non-pasteurized milk, cheese
and other dairy products should
also be avoided.
If you do eat raw vegetables,
soak them in vinegar for 10-15
minutes prior to eating them.
Street vendor foods, which are
common in developing countries
and are not evaluated for health
practices, should also be
Proper hand washing is also
important while abroad and at
Case study
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