Entamoeba histolytica is a pathogenic amoeba that causes amoebiasis (amoebic dysentery). It has two forms - an invasive trophozoite form and a cyst form which is the infectious stage. The cyst can survive for weeks in the environment. Up to 10% of infected individuals develop intestinal or extra-intestinal disease. Symptoms of intestinal disease include diarrhea with blood or mucus while extra-intestinal disease involves the liver or lungs. Diagnosis involves identifying the trophozoites or cysts in stool samples. Treatment is with metronidazole or tinidazole. Prevention focuses on improved sanitation, safe water and hygiene education to prevent fecal-oral

1. Amoebiasis
(Amoebic dysentery)

2. Amoebiasis
Causal agent: Entamoeba histolytica is well
recognized as a pathogenic amoeba.
History: Loosh was first described in 1875
“Harbouring of protozoa E. histolytica inside the body
with or without disease”
 only 10% of infected develop disease
 two types of infection
-Extra-intestinal
-Intestinal- mild to fulminant

3. Causative agent:
Entamoeba histolytica

5. Taxonomic Classification
Kingdom:
Subkingdom
Phylum
Subphylum
Class
Order
Family
Genus
Species
Protista
Protozoa
Sarcomastigophora
Sarcodina
Lobosea
Amoebida
Endamoebidae
Entamoeba
histolytica

6. Etiology:
Five species of Entamoeba:
E. histolytica (Pathogenic),
E. dispar
E. coli,
E. hartmanni,
E. gingivalis

7. Life cycle
cyst postcyst
precyst large trophozoite

8. Morphology
•Different form of E. histolytica;
• 1- trophozoite
• 2- precyst
•3- cyst(1, 2, 4 nuclei)

9. Trophozoite characteristics
• Size: 12-60μm in diameter;
• Non-invasive form ( minuta) / E. dispare
• Invasive form (magna) contain RBC, E. histolytica
• Pseudopodia:
• Motility:
Ectoplasm:
• Endoplasm: may be contain ingested RBC
• Nucleoplasm:
Non-invasive form
invasive form

12. Trends of Amoebiasis

13. Magnitude
Global: - worldwide in distribution
- 3rd most common parasitic death
- India, China, Africa, South America
- 2-60% prevalence
- 100,000 deaths/year
- 500 million infections
- 50 million cases
India: - 15% prevalence (3.6-47.4%)
- variation according to sanitation

14. Epidemiological determinants
Entamoeba histolytica
 7 zymodemes pathogenic
 two forms –
- trophozoite (vegetative)-fragile
- cyst -this is the infective stage
• -survives for weeks if appropr. envi
• -infective dose can be a single cyst
 source of infection is a case or carrier
-1.5*107 cysts per day
 reservoir is only human –several years
 resistant to chlorine in normal conc.
 readily killed by freezing or heating(55°C)

15. Incubation period:
3 days in severe
infection;
several months in
sub-acute and chronic
form.
In average case vary
from 3-4 weeks.
Period of
communicability:
For duration of the
illness.

16. Mode of Transmission
1-driect contact of person to person( fecal-
oral)
2- Veneral transmission among homosexual
males(oral-anal)
3- Food or drink contaminated with feces
containing the E.his. cyst
4- Use of human feces (night soil) for soil
fertilizer
5- contamination of foodstuffs by flies, and
possibly cockroaches, rats, etc.

18. • Host
 All age groups affected
 No gender or racial differences
 Institutional, community living,
Severe if children, old, pregnant,
Develops antibodies in tissue invasion
• Environment
 Low socio-economic
 Poor sanitation, sewage seepage
 Night soil for agriculture
 Seasonal variation

19. Host Factor Contributions
•Several factors contribute to influence infection
1 Stress
2 Malnutrition
3 Alcoholism
4 Corticosteroid therapy
5 Immunodeficiency
6 Alteration of Bacterial flora

20. Risk factors
• People in developing countries that have
poor sanitary conditions
• Immigrants from developing countries
• Travellers to developing countries
• People who live in institutions that have
poor sanitary conditions
• HIV-positive patients
• homosexuals

21. Clinical features
Intestinal
•Asymptomatic
carriers
• Amoebic colitis
• Fulminant colitis
• Amoeboma
Extra intestinal
• Liver
• Lung
• Brain
• Skin

22. Non Invasive Forms:
Asymptomatic carriers
- 90% without symptoms
- does not damage lumen
Invasive forms:
Amoebic colitis
- flask shaped ulcers superficial or deep
- abd pain, diarrhoea, blood, fever
- peri-anal ulcers
Fulminant colitis - <0.5%
- severely ill with high fever
- intestinal bleeding
- perforation
- paralytic ileus

23. Amoeboma
- 1% of cases
- inflammatory thickening of intestinal wall
- palpable mass with trophozoites
Symptoms of amoebic colitis
Symptoms Percentage
1. Diarrhea 100
2. Dysentery 99
3. Abdominal pain 85
4. Fever 68
5. Dehydration 5
6. Length of symptoms 2 to 4 weeks

24. Symptom Bacillary dysentery Amoebic dysentery
Onset Acute Gradual
General
Condition
Poor Normal
Fever High grade Little fever (adult)
Tenesmus Severe Moderate
Dehydration Frequent Little dehydration
(adult)
Faeces No trophozoites Trophozoites present
Culture Positive Negative

25. Extra-intestinal
Amoebic liver abscess
- via portal system
- 5% of invasive disease
- 10 times more common in men
Pleuropulmonary
- direct spread from liver abcess (10%)
- haematogenous spread
Brain
- abrupt onset & rapid progression
- death in 12-72 hrs

26. Virulence factors
•Trophozoites of E.histolytica interact with host through a
series of steps:
1. Adhesion of target cell, phagocytosis and cytopathic
effect
2. E.histolytica induces both Humoral and cell mediated
immune responses.
3. Virulence factors – In many circumstances lumen dwelling
Amoeba may be asymptomatic
4. Causes disease only when invade the Intestine
5. Virulence is associated with secretion of Cysteine
proteniase which assists the organism in digesting the
extracellular matrix and invading tissues

27. Cysteine proteinase - Complement factor C3
•It is observed Cysteine
proteinase produced by
invasive strains of
E.histolytica inactivates
the complement factor C3
and are thus resistant to
Complement mediated
lysis.

28. Zymodeme
•Zymodeme: Populations of
parasites with identical isoenzymes.
•Based on Electrophoretic mobility
E.histolytica strains are classified into
22 Zymodemes
•However only 9 are invasive

29. Invasive x Noninvasive strains
•The invasive and non invasive
strains may appear identical
may represent two distinct
species
•1. Invasive strain –
E.histolytica
•2. Non invasive strains
reclassified as E.dispar.

30. Pathogenesis
Effective factors:
1- strain virulence:
- classic strain
- non-classic strain; Laredo , Huff, ….
- pathogen zymodemes
2- susceptibility of the host; nutrition status, immune-sys.
3- breakdown of immunologic barrier (tissue invasion)

31. Pathogenicity mechanisms
• 1- secreting proteolytic enzymes( histolysine )
and cytotoxic substances.
• 2 - contact-dependent cell killing
• 3 – cytophagocytosis
Amebic killing target cell:
• 1- Receptor-mediated adherence of amebae to target cell (adherence
lectin)
• 2- Amebic cytolysis of target cell
• 3- Amebic phagocytosis of killed target cell

44. Clinical manifestation
A. Acute amoebic dysentery
Slight attack of diarrhea, altered
with periods of constipation and
often accompanied by tenesmus.
Diarrhea, watery and foul-smelling
stools often containing blood-
streaked mucus.
Diarrhea, watery and foul-smelling
stools often containing blood-
streaked mucus.
Nausea, flatulence and abdominal
distension, and tenderness in the
right iliac region over the colon.

45. B. Chronic amoebic dysentery
Attack of dysentery lasting for several days,
usually succeeded by constipation.
Tenesmus accompanied by the desire to
defecate.
Anorexia, weight loss and weakness.
Liver maybe enlarged.
The stools at first are semi-fluid but soon
become watery, blood, and mucoid.
Vague abdominal distress, flatulence,
constipation or irregularity of the bowel.
Mild anorexia, constant fatigue and lassitude
Abdomen lost its elasticity when picked---up
between fingers.
On sigmoidoscopy, scattered ulceration with
yellowish and erythematous border.
Gangrenous type of stool

46. Diagnosis
 Diagnosis
- fresh mucus or rectal ulcer swab
- colourless motile trophozoites with RBC
- quadrinucleated cysts
 Serology –IHA, ELISA
- usually negative in intestinal

54. Quadrinucleated cyst

55. Drug
Metronidazole Tinidazole Iodoquinol Diloxanide
furoate
Acts
on
Kills
trophozoites in
intestine & tissue
Kills
trophozoites
in intestine &
tissue
Luminal-
Eradicate
cysts
Luminal-
Eradicate
cysts
Dose 500-750 mg PO
tid x 5-10 days
600 mg bd
PO x 5 days
650 mg PO
tid x10days
500 mg PO
tid x10days
Treatment
- symptomatic cases
- asymptomatic in non-endemic areas
- asymptomatic if food handlers

56. Prevention & Control
Primary prevention
- Safe excreta disposal
- Safe water supply
- Hygiene
- Health education
Secondary
- Early diagnosis
- Treatment

57. Primary prevention
Sanitation Water Food hygiene H edu.
-excreta -protect -protect food -long
-wash hands -sand filter -acetic acid term
-latrines -boiling -detergent
-food handlers
examine
treat
educate