Entamoeba Histolytica by Dr. Rakesh

1. Entamoeba histolytica
Dr. Rakesh Prasad Sah
Associate Professor, Microbiology

2. Introduction to Parasitology
› Terms used in Parasitology:
 Parasite: A living organism which receives nourishment & shelter from
another organism where it lives.
 Host: An organism which harbours the parasite.
› Classes of Parasites:
› 1.Ectoparasite-lives on the surface of the body of host.
– Ex- lice, mites, ticks(arthropods)
› 2.Endoparasite-lives inside the body of host ie- in blood, tissues, digestive
tract ect.
– Ex-All protozoan & helminthic parasites of man.
› 3.Temporary parasite-visits its host for a short period.

3. › 4.Permanent parasite-leads a parasitic life throughout the whole
period of its life.
› 5.Facultative parasite-lives a parasitic life when opportunity arises.
› 6.Obligatory parasite-cannot exist without a parasitic life.
› 7.Accidental parasite-attacks an unusual host.
› 8. Wandering parasite-happens to reach a place where it cannot live.

4. Classes of Hosts:
› Definitive host: which harbours the adult stage of the parasite or host in
which sexual multiplication takes place. ex. In malaria mosquito is def…host. In
hydatid disease dog.
› Intermediate host: which harbours larval stage of parasite or host in which
asexual multiplication of parasite occurs.ex.in malaria and Hydatid disease man
is Int…host.
› Zoonotic diseases: (zoonosis)-Diseases that are transmitted from animals to
humans
– Ex-hydatid disease

5. Classification
› Medically Imp. Parasites: 2 kingdoms
› 1)Protista 2)Animalia
Phyllum-Protozoa Helminths
Protozoa- unicellular, Microscopic. Helmints-
Multicelular, Macro.
* single cell performs all functions. Each special cell
performs particular
function

6. › Medical protozoalogy
4 classes
1.Rhizopoda ex. Entamoeba
2.Flagellates ex. Haemoflagellates & Intestinal Flagellates
3.Sporozoa ex. Plasmodium & Toxoplasma
4.Ciliates ex. Balantidium coli
Helminths : 2 phylum-
1. Platyhelminthes (Flat worms)
2. Nemathelminthes (Round worms)
i. Platyhelminthes- 2 classes-
1. cestodes(Tape worms) Tape like segments
2. Trematodes (Flukes) Leaf like, unsegmented
ii. Nemathelminths- (Round worms)-Cylindrical, Elongated, Unsegmented

7. › In General all parasites are classified in to
 Kingdom – protista
 Phylum – protozoa/ sarcomestigophora
 Subphylum – plasmodroma/ Sarcodina
 Class – rhizopoda(Amoebae)
 Order – Amoebida
 Genus – Entamoeba
 Species – histolytica

8. › The systematic study of parasite involves the knowledge of :
› 1. Geographical Distribution-Area where it is found
› 2. Habitat- Place where the parasite resides in the host
› 3. Morphology- Various developmental stages of parasites through which
it passes in its life cycle are studied
› Ex. Trophozoites, cysts, Larva, Adult worm
› 4. Modes of Infection-
› Sources of Infection:
› i. Contaminated food & water
› ii. Contaminated soil polluted with human faeces
› iii. Different animals
› iv. Insect vectors

9. › Portal of entry
› i. By ingestion (faeco oral route)
› ii. By Ingesting the parasite in raw under cooked meat
› iii. By penetration of skin with the larva
› iv. Through insect bite (vectors)
› 5.Life Cycle – Cycle of development of a parasite. The parasite may
pass its life cycle in one and the same host or it may change its host.
› 6. Lab Diagnosis – Following material should be collected.
› 1.Blood- For those parasites which infect blood stream.
› 2.Stool- for diagnosing intestinal parasites.
› 3.Urine- Parasites in the urinary tract.
› 4.sputum- In respiratory tract.

10. › 5.Biopsy Material
› 6.Indirect evidence-
› i.Change in the blood, Eosinophilia, Leucopenia, Anaemia
› ii. serological tests.
› Iii. Skin tests (Intradermal reaction)
› Emerging parasites- (Newly arising pathogen)
› 1.Cryptosporidium- Intestinal parasite
› 2.Isospora- Intestinal parasite
› Commensals but now a days these are important organism because
of their association with HIV inf & Aids in which they cause severe
infection.

11.  AMOEBA- Protozoa: unicellular, all functions like reproduction,
digestion,respiration,excretion
 Microscopic .Basic structure- protoplasm enclosed in cell
membrane. Protoplasm differentiated into cytoplasm& Nucleus.
 Exhibit movements by cilia, flagella, pseudopodia.
 Classification:
 Intestinal species:1.Entamoeba histolytica
 2.E.hartmanni 3.E.coli 4.E.polecki.
 Endolimax nana. 6.Iodamoeba butschlii.
 Extra intestinal-1.Entamoeba gingivalis.
 2. Acanthamoeba sp. 3.Naegleria fowleri.

12. Entamoeba histolytica
› Entos = inside + amoibs = changing; histos = tissue + luein = to dissolve
› Was first described by Losch in 1875 after being isolated in Russia from a patient
with dysenteric tool.
› Only amoeba to have definite pathogenic potential is Entamoeba histolytica, a
major cause of bloody diarrhea (dysentery) and extra-intestinal invasive disease
in humans.
› 2nd most common parasitic cause of mortality (after malaria), accounting for an
estimated 55,000 deaths each year.
› Risk factors
– Young age, pregnancy, corticosterioid use, alcoholism, malignancy, malnutrition etc.

13. Morphology
› E. histolytica
– Trophozoite
– Pre-cyst
– Cyst
– Metcyst
› Trophozoite (Trophe = Food + Zoon = animal)
› It is amoeboid in shape
› 20-30µm in size (though it could range from 10-
60µm)
› Actively motile in fresh stool with short hyaline
pesudopodia

14. Morphology
› Cytoplasm  visible with a clear, thin ectoplasm on the outside and a granular “ground
glass” endoplasm inside.
› Iron hematoxylin stain  clear visualization of nucleus  single, spherical with a
compact karyosome at its centre.
› Inner layer of nuclear membrane  lined with evenly distributed fine chromatin
granules.
› Food vacuoles with ingested RBCs and bacteria can often be seen.

15. Cyst (Kystis=bladder)
› Trophozoite condense to form Pre-
cysts  mature cysts (10x20µm)
› An early cyst has one nucleus 
divides into two or four nuclei
(metacyst) on maturation.

16. Life cycle: (simple) man is the only host
Quadrinucleated cyst
Human (by ingestion)
Cyst (pass upto ileo-ceacal region)
Excystation occur (due to surrounding
alkalinity and damage by trypsin to cyst wall)
Quadrinucleate cyst

17. Life cycle: (simple) man is the only host
Divide 8 small ameobae (amoebulae or metacystic
trophozoites)
Develops into trophozoites
Large intestine – live in the lumen without invading
intestinal mucosa (90% infected persons)
They encyst when conditions becomes unfavorable -Cyst
in feces (carriers)- maintainence & spread of infection in
community
In remaining 10 % infected persons – amoebae invade the
host tissue ( bowel mucosa- causes dysentry)

19. Pathogenesis
Human infected with cystic forms of E. histolytica
After excystation, some amoeba colonises large
intestine manifests from carrier state to diarrhoea or
invasive disease.
Several virulence factors causes extensive tissue
destruction by lysing host cells.
Mechanism of pathogenesis of infection:- Adherence
by galactose and N-acetyl D-galactosamine lectin
(Gal/GalNAc) to epithelial cells and other target cells.
Mucin facilitates binding of parasite and protects the
intestinal epithelium from direct lysis.

20. Pathogenesis
Cytolysis:- extensive cytolysis brought by Gal/GalNAc
lectin and other amoebaphores
Cell death results from swelling, chromatin
condensation, membrane blebbing, DNA fragmentation
and non-classsical apoptosis.
Phagocytosis:- amoeba ingests cell debris and RBCs.
Cysteine proteases:- responsible for the degradation and
digestion of mucin glycoproteins, Hb, villin and
extracellular matrix (fibronectin, laminin, elastin and
collagen)

21. Intestinal Amoebiasis
› Causes disruption of the epithelium and the depletion of the mucus 
followed by formation of ulcers.
› Lesions commonly develop
– Caecum
– Rectum
– Ascending colon
– Sigmoid colon
– Rarely transverse and
descending colon.
› Further invasion of submucosa and underlying blood vessels facilitates
migration of trophozoites to liver, lungs and other organs from secondary
lesions.

22. Extra-intestinal Amoebiasis
› Commonest secondary lesion  liver abscess 
postero-superior surface of the right lobe of the liver.
› The pus of is made up of
– Liquified necrotic liver tissue and blood (thick
chocolate brown)
– Contains few leukocytes
– Bacteriologically sterile
› Trophozoite carried via the blood stream  cause
metastatic abscesses anywhere in the body.

23. Clinical Features
› I.P.  1-4 weeks.
Asymptomatic disease
› 90% of the infections remain asymptomatic or mildly symptomatic.
Symptomatic disease
› Diarrhea
– Gradual onset of lower abdominal pain and mild diarrhea
– Malaise, weight loss and diffuse lower abdominal pain
– Occasionally progressing to dysentery.

24. Clinical Features
› Amoebic dysentery
– Onset is gradual
– Colicky abdominal pain
– Fever
– Prostation
– Bloody diarrhea with mucus and pus cells.
– Resembles bacillary dysentery, a few clinical and laboratory features help to
differentiate between two entites.

25. Differential features of amoebic and bacillary dysentery
S.No. Clinical Features Amoebic dysentery Bacillary Dysentery
1 Onset Gradual Acute
2 Fever Present in <40% Almost always present
3 Abdominal tenderness Localised to the right upper quadrant
of the abdomen or referred to the
shoulder
Generalised
4 Tenesmus Absent Present
Stool Sample
5 Odour Offensive Not offensive
6 Colour Dark red Bright red
7 Nature Scanty feces mixed with blood and
mucus; hme-positive
Blood and mucus with little or no
feces
8 Consistency Not adherent to container Adherent to container
9 Reaction Acidic Alkaline

26. › Amoebic appendicitis
– Acute right lower abdominal pain that mimics appendicitis.
› Amoeboma
– May present as a palpable abdominal mass  confused with carcinoma.
› Fulminant colitis or toxic megacolon
– Intense colicky pain
– Fever
– Profuse bloody diarrhea
– Mortalitiy rate is very high (40%) in patients with corticosteroid therapy
– Note:- so important to exclude amoebiasis in patients with inflammatory bowel disease.
› Chronic non-dysenteric colitis
– Resembles inflammatory bowel disease with potentially severe consequences if corticosteroids
are administered.

27. Extra-intestinal Amoebiasis
› Hepatic involvement  most common extra-intestinal complications of
amoebiasis  reported in 2-10% of the individuals infected with E. histolytica.
S. No. Clinical Features Amoebic liver abscess (ALA) Pyogenic abscess
1 Age 20-40 >50
2 Male:female ratio 10:1 1:1
3 Number of abscesses Solitary abscess in 80% of chronic
ALA cases and about 50% of acute
ALA
Multiple abscesses in approx
50% of all cases
4 Diabetes mellitus Less common, approximately 2% of
patients
More common, approx one
fourth of the patients
5 Jaundice Uncommon Common
6 Pruritus Uncommon Common
Elevated bilirubin Uncommon Common
Elevated liver enzymes Uncommon Common

28. › ALA present with
– fever
– Abdominal pain localised to the right upper quadrant
– Weight loss
– Pain may radiate to the right shoulder and my be accompanied by a non-productive
cough.
– On, examination  tenderness of the liver, hepatomegaly, jaundince less common.
– ALA tend to rupture into the adjacent tissues and may affect other body organs.

29. Pulmonary amoebiasis
› Lung
– involved by extension of liver abscess through diaphragm or
– by direct hematogenous spread from the intestine.
– Hepato-bronchial fistula  results with expectoration of chocolate brown sputum  amoeba
can be demonstrated.
› Cutaneous amoebiasis
› Other organ involvement
– Abscesses may develop in (through hematogenous route)
› Brain (fatal)
› Spleen
› Kidney
› Genitourinary organ
› adrenals

30. Diagnosis of Intestinal Amoebiasis
› Microscopy
– Trophozoites and cysts
– Direct microscopy of stool using wet mount and iodine mount

31. Diagnosis of Intestinal Amoebiasis
› Culture
– NIH (National institurte of health) media, Boeck and Drbohlav egg serum
medium containing Locke’s solution, Balamuth’s medium and diamond’s
medium
– Zymodeme/isoenzyme analysis
› Coproantigen detection: ELISA and immunochromatographic tests
› DNA detection: PCR and real-time PCR.

32. Diagnosis of Amoebic Liver Abscess (ALA)
› Microscopy
– Trophozoites and cysts
– Direct microscopy of aspirated pus and sputum (Pulmonary rupture)
› Culture
– NIH (National institurteu of health) media, Boeck and Drbohlav egg serum medium containing Locke’s
solution, Balamuth’s medium and diamond’s medium
– Zymodeme/isoenzyme analysis
› Ag detection:- ELISA and immunochromatographic tests
› DNA detection: PCR and real-time PCR.
› Other diagnostic parameters:
– Leukocytosis,
– Alkaline phosphatase
– Radiology  ultrasonography