Amoeba are structurally simple protozoans that can invade and damage the intestinal tract. Entamoeba histolytica is an intestinal amoeba that can cause amoebic dysentery or form extra-intestinal abscesses in the liver and lungs. E. histolytica was first discovered in 1875 and exists in trophozoite, precyst, and cyst forms. The cyst form is infectious and can be transmitted through contaminated food or water. In the intestine, trophozoites may invade the colonic mucosa, causing ulcers or abscesses with symptoms of bloody diarrhea. Liver abscesses are a common extraintestinal manifestation and can spread infection to other organs.

2.  Amoeba are structurally simple protozoans
which have no fixed shape
 Phylum : Sarcomastigophora
 Subphylum :Sarcodina
 Super class :Rhizopoda
 Order : Amoebida

3. Amoeba
Free living
Intestinal
 Entamoeba histolytica is an intestinal
amoeba
 All intestinal amoebae are non pathogenic
except Entamoeba histolytica
 All free living amoeba are oppurtunistic
pathogens.

4.  E. histolytica was discovered by Losch in
1875
 Demonstrated the parasite in the dysenteric
feces of a patient in St.Petersburg in Russia.

5.  MORPHOLOGY
 LIFE CYCLE
 PATHOGENESIS & CLINICAL FEATURES
 LABORATORY DIAGNOSIS
 TREATMENT
 PREVENTION

6.  E.histolytica occurs in 3 forms
Trophozoite
Precyst
Cyst

7.  Vegetative or growing stage of the parasite
 Only form present in tissues
 Irregular in shape
 Size: 12-60 μm( Average 20μm)
 Large and actively motile in freshly passed
dysenteric stool, while smaller in
convalescents and carriers.
 In the lumen, commensal and small in
size(15-20 μm)-MINUTA FORM

9. Cytoplasm
Outer ectoplasm-clear,transparent,
refractile.
Inner endoplasm-finely granular
(ground glass appearance),with
nucleus
food vacuoles
erythrocytes
leucocytes(occasionally)
tissue debris

10.  Pseudopodia
Fingerlike projections formed by
sudden jerky movements of ectoplasm in one
direction, followed by the streaming in of
the whole endoplasm
 Typical amoeboid motility is a Crawling or
Gliding
 Pseudopodia formation and motility are
inhibited at low temperature

11. Nucleus
 It is spherical 4-6μm in size
 contains central karyosome,surrounded by
clear halo and anchored to the nuclear
membrane by fine radiating fibrils called the
Linin network , giving a cartwheel
appearance
 Nuclear membrane is lined by a rim of
chromatin distributed evenly as small
granules

12.  Trophozoites from acute dysentric stools
often contain phagocytosed erythrocytes-
diagnostic feature ,these are not found in
any other commensal intestinal amoeba
 These divided by binary fission in every 8
hours
 These are killed by drying, heat ,and
chemical sterilization
 Infections are not transmitted by these-
destroyed in stomach and cannot initiate
infection

13.  Trophozoites undergo encystment in the
lumen
 Before encystment,the trophozoites
extrudesits food vacuoles and become round
or oval,10-20µm in size-precyst
 Contains a large glycogen vacuole and two
chromatid bars
 It then secretes a highly retractile cyst wall
around it and become cyst

15.  Spherical ,10-20µm
 3 types of cyst
Early cyst
Binucleate cyst
mature quadrinucleate cyst
Early cyst
contains a single nucleus and two other
structures-a mass of glycogen and 1-4
chromatid bodies or chromadial bars

16.  As the cyst mature, the glycogen mass and
chromidial bars disappear and the nucleus
undergoes 2 succesive mitotic divisions to
form 2 and then 4 nuclei .
 The cyst wall is a highly resistant to gastric
juice and unfavorable environmental
conditions

17.  Infective form :mature quadrinucleate cyst
passed in feces of convalscents and carriers
 Mode of transmission :man acquires infection
by swallowing food and water contaminated
with cyst .
 Stomach –cyst wall is resistant to gastric
juice
 Exystation :cyst reaches the caecum or lower
part of ileum ,due to alkaline medium ,cyst
wall damaged by trypsin ,leading to
exystation

20.  E.histolytica causes intestinal and extra
intestinal amoebiasis
Intestinal amoebiasis -PATHOGENESIS
Lumen dwelling amoeba do not cause any
illness .They causes disease only when they
invade the intestinal tissues .
10 % -symptomatic
90% -asymptomatic

21.  Not all strains of E.histolytica are pathogenic or
invasive .
 Differentiation between pathogenic and non
pathogenic strains can be made by
 susceptibility to complement-mediated lysis
 Phagocytic activity
 by the use of genetic markers
 monoclonal antibodies
 Zymodeme analysis

22.  The metacystic trophozoites penetrate the columnar
epithelial cells of crypts of Liberkuhn
 Penetration is facilitated by
motility of the trophozoites
tissue lytic enzyme –histolysin
amoebic lectin -mediate adherence
 Mucosal penetration by amoeba produce discrete
ulcers with pinhead center and raised edges .
 Sometimes invasion remains superficial and heal
spontaneously.
 More often, the amoeba penetrates to submucosal
layer and multiplies rapidly- lytic necrosis- abscess-
ulcer

23.  Ulcer appear initially on the mucosa as raised
nodules with pouting edges .
 They breakdown discharging brownish
necrotic material contains large numbers of
trophozoites.
 The typical amoebic ulcer –flask shaped
 Multiple ulcers may coalesce to form large
necrotic lesions with ragged and undermined
edges,covered with brownish slough

24.  The ulcers generally do not extend deeper
than submucosal layer.
 Occassionally, a granulamatous
pseudotumoral growth may develop on the
intestinal wall from a chronic ulcer.This
amoebic granuloma or amoeboma may be
mistaken for are malignant tumor

25.  Small superficial ulcers involving only the mucosa
 Round or oval shaped with ragged and undermined margin
and flask-shaped in cross section
 Marked scarring of intestinal wall with thining ,dilatation
,and sacculation
 Extensive adhesions with neighboring viscera
 Formation of tumor-like masses of granulation tissue
amoeba

26.  The incubation period is highly variable from
1-4 months
 The clinical course is characterized by
prolonged latency,relapses and intermissions.
 Typical manifestation is amoebic dysentry
 Compared to bacillary desentry ,it is usually
insidious in onset and the abdominal
tenderness is less and localised.
 The stools are large, foul-smelling,and
brownish black, often with bloodstreaked
mucus intermingled with feces.

28.  The RBCs in stools are clumped and reddish
brown in color.
 Cellular exudate is scanty.
 Charcot-leyden crystals are often present.
 The patient is usually afebrile and non toxic.
 In fulminant colitis, there is confluent
ulceration and necrosis of colon-patient is
febrile and toxic.

29.  Intestinal amoebiasis not always result in
dysentry.quite often there may be only
diarrhea or vagueabdominal symptoms
popularly called uncomfortable belly or
growling abdomen.
 Chronic involvement of the caecum causes a
condition simulating appendicitis.

30.  Fulminant amoebic colitis
toxic megacolon
perianal ulceration
Amoeboma
 Extra intestinal Amoebiasis
amoebic hepatitis
amoebic liver abscess
amoebic appendicitis and peritonitis
pulmonary amoebiasis
cerebral amoebiasis
splenic abscess
cutaneous amoebiasis
genitourinary amoebiasis

33.  Hepatic Amoebiasis
 Pulmonary Amoebiasis
 Metastatic Amoebiasis
 Cutaneous Amoebiasis
 Genitourinary Amoebiasis

34.  Most common extra intestinal amoebiasis .
 The history of amoebic dysentry is absent in
more than 50% cases
 Several patients with amoebic colitis develop
an enlarged tender liver without detectable
impairment of liver function or fever.
 This acute hepatic involvement (amoebic
hepatitis) may be due to repeated invasion
by amoeba from an active colonic infection
or to toxic substance from the colon reaching
the liver.

35.  In about 5-10% of person with intestinal
amoebiasis ,liver abscesses may ensue.
 The center of the abscess contains thick
chocolate brown pus(anchovy pus),which is
liqeefied necrotic liver tissue.
 At the periphery, there is almost normal
liver tissue,which contain invading amoeba.
 Liver abscess may
multiple
solitary

36.  Usually located on right lobe of liver
 Jaundice develops
only when lesions are multiple OR
when they press on the biliary tract
 Incidenca of liver abscess is less common in
women and rare in children under age of 10

37.  It may occure by direct hematogenous spread
from colon bypassing the liver,but it most
often follows extension of hepatic abscess
through the diaphragm
 Hepatobronchial fistula usually results with
expectoration of chocolate brown sputum
 Patient presents with
severe pleuritic chest pain
dyspnea
non-productive cough

38.  Involvement of distant organs is by
hematogenous spread and through
lymphatics
 Abscess in
Kidney
Brain
Spleen
Adrenals
Spread to brain leads to severe destruction of
brain tissues and is fatal

39.  It occurs by direct extension around anus,
colostomy site,or discharging sinuses from
amoebic abscess .
 Extensive gangrenous destruction of the skin
occurs .
 The lesion may be mistaken for condyloma or
epithelioma

40.  Penile amoebiasis
prepuce and glans are affected
acquired through anal intercourse
In females
 vulva ,vagina, or cervix
 by spread from perineum
 destructive ulcerative lesions resemble
carcinoma

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