This document provides information about amebiasis (amebic dysentery), caused by the protozoan Entamoeba histolytica. It discusses the causal agent, geographic distribution, morphology, life cycle, epidemiology, transmission, pathogenesis, clinical symptoms, diagnosis, treatment, and pathology of intestinal and extraintestinal amebiasis. Key points include that amebiasis is widespread in developing countries and causes an estimated 50,000-100,000 deaths annually, and that differentiating E. histolytica from the nonpathogenic E. dispar requires identification of erythrophagocytosis or molecular/immunological methods.

1. ‫الرحیم‬ ‫الرحمن‬ ‫ال‬ ‫بسم‬

2. AmebiasisAmebiasis
(Amebic Dysentery)(Amebic Dysentery)
Dr. M.H.ANVARIDr. M.H.ANVARI

3. AmebiasisAmebiasis
(Amebic Dysentery(Amebic Dysentery((
Causal agentCausal agent:: Entamoeba histolyticaEntamoeba histolytica is well recognizedis well recognized
as a pathogenic amoeba.as a pathogenic amoeba.
Geographic DistributionGeographic Distribution: Worldwide, with higher: Worldwide, with higher
incidence of amebiasis in developing countries.incidence of amebiasis in developing countries.
In industrialized countries, risk groups include maleIn industrialized countries, risk groups include male
homosexuals, travelers and recent immigrants, andhomosexuals, travelers and recent immigrants, and
institutionalized populations.institutionalized populations.
History: Loosh was first described in 1875

4. MorphologyMorphology
 Different form of E. histolytica;Different form of E. histolytica;
 1- trophozoite1- trophozoite
 2- precyst2- precyst
 3- cyst(1, 2, 4 nuclei)3- cyst(1, 2, 4 nuclei)

5. Trophozoite chractereTrophozoite chractere
 SizeSize:: 12-6012-60μμmm
in diameterin diameter;;

Non-invasive form ( minuta( / E. dispareNon-invasive form ( minuta( / E. dispare
 Invasive form (magna) contain RBC, E. histolyticaInvasive form (magna) contain RBC, E. histolytica
 PseudopodiaPseudopodia::
 MotilityMotility::
EctoplasmEctoplasm::
 EndoplasmEndoplasm:: may be contain ingestedmay be contain ingested RBCRBC
 NucleoplasmNucleoplasm::
Non-invasive form
invasive form

6. Different form of E.histolytica cystDifferent form of E.histolytica cyst

7. Life cycleLife cycle
Life cycle

8. EpidemiologyEpidemiology
 PrevalencePrevalence of amebic infection varies with level of sanitationof amebic infection varies with level of sanitation
and generally higher in tropics and subtropics than inand generally higher in tropics and subtropics than in
tempearate climates.tempearate climates.
 *Worldwide prevalence is about 10% to 50%*Worldwide prevalence is about 10% to 50%
 **Cyst passersCyst passers are important source of infectionare important source of infection
 The true estimated prevalence of E. histolytica is close to 1%The true estimated prevalence of E. histolytica is close to 1%
worldwide.worldwide.
 Entamoeba histolyticaEntamoeba histolytica is the second leading cause ofis the second leading cause of
mortality due to parasitic disease in humans. (The first beingmortality due to parasitic disease in humans. (The first being
malaria). Amebiasis is the cause of an estimatedmalaria). Amebiasis is the cause of an estimated 50,000-50,000-
100,000100,000 deaths each year.deaths each year.

9. TransmissionTransmission
 1-driect contact of person to person( fecal-oral)1-driect contact of person to person( fecal-oral)
 2- Veneral transmission among homosexual2- Veneral transmission among homosexual
males( oral-analmales( oral-anal
 3- Food or drink contaminated with feces containing3- Food or drink contaminated with feces containing
the E.his. cystthe E.his. cyst
 4- Use of human feces (night soil) for soil fertilizer4- Use of human feces (night soil) for soil fertilizer
 5- contamination of foodstuffs by flies, and possibly5- contamination of foodstuffs by flies, and possibly
cockroachescockroaches

10. PathogenesisPathogenesis
 Effective factores:Effective factores:
 1- strain virulence1- strain virulence::
- classic strain- classic strain
- non-classic strain; Laredo , Huff, ….- non-classic strain; Laredo , Huff, ….
- pathogen zymodemes- pathogen zymodemes
 2- susceptibility of the host; nutrition status, immune-sys.2- susceptibility of the host; nutrition status, immune-sys.
 3- breakdown of immunologic barrier (tissue invasion)3- breakdown of immunologic barrier (tissue invasion)

11. Pathogenicity mechanismsPathogenicity mechanisms
 1- secreting proteolytic enzymes( histolysine )1- secreting proteolytic enzymes( histolysine )
and cytotoxic substances.and cytotoxic substances.
 2 - contact-dependent cell killing2 - contact-dependent cell killing
 3 – cytophagocytosis3 – cytophagocytosis
 Amebic killing target cell:Amebic killing target cell:
 1- receptore-mediated adherence of amebae to target cell ( adherence1- receptore-mediated adherence of amebae to target cell ( adherence
lectin)lectin)
 2- amebic cytolysis of target cell2- amebic cytolysis of target cell

3- amebic phagocytosis of killed target cell3- amebic phagocytosis of killed target cell

13. Clinical symptomsClinical symptoms
Asymptomatic infection Symptomatic infectionAsymptomatic infection Symptomatic infection
Intestinal Amebiasis Extraintestinal AmebiasisIntestinal Amebiasis Extraintestinal Amebiasis
Dysenteric Non-Dysenteric colitisDysenteric Non-Dysenteric colitis Hepatic Pulmonary The extraHepatic Pulmonary The extra focifoci
Liver abscces Acut nonsupprativeLiver abscces Acut nonsupprative
Intestinal Amebiasis symptoms:Intestinal Amebiasis symptoms: Diarrhea or dysentery, abdominal pain, cramping , anorexia,Diarrhea or dysentery, abdominal pain, cramping , anorexia,
weight loss, chronic fatigueweight loss, chronic fatigue

15. Pathology of AmebiasisPathology of Amebiasis

16. Flask-like UlcerFlask-like Ulcer

17. Extra-ntestinalAmebiasisExtra-ntestinalAmebiasis

18. Pyogenic- Liver AbscessPyogenic- Liver Abscess

20. Liver abscessLiver abscess

21. This is an amebic abscess of liver. Abscesses may arise in liver when there is seeding of
infection from the bowel, because the infectious agents are carried to the liver from the
portal venous circulation.

23. DiagnosisDiagnosis
 Paraclinical Diagnosis:Paraclinical Diagnosis:
 Sigmoidoscopic examination:Sigmoidoscopic examination:
precence of a grossly normal mucosa between the ulcers serves toprecence of a grossly normal mucosa between the ulcers serves to
differentiate amebic from bacillary dysentery,( the entire mucosa beingdifferentiate amebic from bacillary dysentery,( the entire mucosa being
involvoed in bacillary dysentery).involvoed in bacillary dysentery).
 HepatomegallyHepatomegally
 C.B.C. :C.B.C. : leukocytosis in Amebic dys. rises above 12000 perleukocytosis in Amebic dys. rises above 12000 per
microliter, but counts may reach 16000 to 20000 per microliter.microliter, but counts may reach 16000 to 20000 per microliter.

24. Laboratory DiagnosisLaboratory Diagnosis
 Entamoeba histolyticaEntamoeba histolytica must be differentiated from other intestinalmust be differentiated from other intestinal
protozoa including: E. coli, E. hartmanni, E. dispare,……protozoa including: E. coli, E. hartmanni, E. dispare,……
 Differentiation is possibleDifferentiation is possible,, but not always easy, based on morphologicbut not always easy, based on morphologic
characteristics of the cysts and trophozoites.characteristics of the cysts and trophozoites.
 The nonpathogenicThe nonpathogenic Entamoeba disparEntamoeba dispar,, however, is morphologicallyhowever, is morphologically
identical toidentical to E. histolyticaE. histolytica,, and differentiation must be based onand differentiation must be based on
isoenzymaticisoenzymatic oror immunologic analysisimmunologic analysis..
 Molecular methods are also useful in distinguishing betweenMolecular methods are also useful in distinguishing between E.E.
histolyticahistolytica andand E. disparE. dispar and can also be used to identifyand can also be used to identify E.E.
poleckipolecki..

25. MicroscopyMicroscopy
 Microscopic identificationMicroscopic identification
This can be accomplished using:This can be accomplished using:
 Fresh stool: wet mounts and permanently stained preparationsFresh stool: wet mounts and permanently stained preparations
(e.g., trichrome).(e.g., trichrome).
 Concentrates from fresh stool: wet mounts, with or withoutConcentrates from fresh stool: wet mounts, with or without
iodine stain, and permanently stained preparations (e.g.,iodine stain, and permanently stained preparations (e.g.,
trichrome).trichrome).

26. Trophozoites ofTrophozoites of Entamoeba histolyticaEntamoeba histolytica //EE..
dispardispar (( trichrome staintrichrome stain ))
Microscopy
A
B
In the absence of erythrophagocytosis, the pathogenic E. histolytica is
morphologically indistinguishable from the nonpathogenic E. dispar!
Each trophozoite has a single nucleus, which has a centrally placed karyosome
and uniformly distributed peripheral chromatin.

27. Trophozoites ofTrophozoites of Entamoeba histolyticaEntamoeba histolytica with ingestedwith ingested
erythrocyteserythrocytes ((trichrome staintrichrome stain))
The ingested erythrocytes appear as dark inclusions.
Erythrophagocytosis is the only morphologic characteristic that can be
used to differentiate E. histolytica from the nonpathogenic E. dispar.
E F

28. Cysts ofCysts of Entamoeba histolyticaEntamoeba histolytica
//EE.. dispardispar
 GHIGHI
H I
Cysts of Entamoeba histolytica/E.
dispar, permanent preparations stained
with trichrome.

29. ImmunodiagnosisImmunodiagnosis
(Antibody Detection(Antibody Detection((
 1- Antibody detection
 2- Antigen detection may be useful as an adjunct to
microscopic diagnosis
 The indirect hemagglutinationThe indirect hemagglutination ((IHAIHA))
 The EIA test detects antibody specific forThe EIA test detects antibody specific for E. histolyticaE. histolytica inin
approximately 95% of patients with extraintestinal amebiasis,approximately 95% of patients with extraintestinal amebiasis,
70% of patients with active intestinal infection, and 10% of70% of patients with active intestinal infection, and 10% of
asymptomatic persons who are passing cysts ofasymptomatic persons who are passing cysts of E. histolyticaE. histolytica..

30. Antigen DetectionAntigen Detection
Antigen detection may be useful as an adjunct to microscopicAntigen detection may be useful as an adjunct to microscopic
diagnosis in detecting parasites and to distinguish betweendiagnosis in detecting parasites and to distinguish between
pathogenic and nonpathogenic infectionspathogenic and nonpathogenic infections..
Recent studies indicate improved sensitivity and specificity ofRecent studies indicate improved sensitivity and specificity of
fecal antigen assays with the use of monoclonal antibodiesfecal antigen assays with the use of monoclonal antibodies
which can distinguish betweenwhich can distinguish between EE.. histolyticahistolytica andand EE.. dispardispar
infectionsinfections..

31. Molecular diagnosisMolecular diagnosis
 In reference diagnosis laboratories, PCR is theIn reference diagnosis laboratories, PCR is the
method of choice for discriminating betweenmethod of choice for discriminating between
the pathogenic speciesthe pathogenic species ((EE.. histolytica)histolytica) from thefrom the
(nonpathogenic species(nonpathogenic species ((EE.. dispardispar..

32. TreatmentTreatment
 Intestinal Amebiasis:Intestinal Amebiasis:
 **Asymptomatic amebiasis(cyst passer)Asymptomatic amebiasis(cyst passer):: Diloxanide furoateDiloxanide furoate
( furamide)( furamide)
500 mg 3 times daily / 10 days500 mg 3 times daily / 10 days
 **Symptomatic amebiasis ( troph. & cyst):Symptomatic amebiasis ( troph. & cyst): - Iodoquinol , 650 mg 3- Iodoquinol , 650 mg 3
times daily/ 20 days or Metronidazole (Flagyl) , 750 mg 3 times daily/ 10times daily/ 20 days or Metronidazole (Flagyl) , 750 mg 3 times daily/ 10
daysdays
 *Amebic*Amebic colitis: Chloroquine, 250 mg 2 times dailycolitis: Chloroquine, 250 mg 2 times daily
 * Acute amebic dysentery: Emetine hydrochloride, 1mg/kg daily IM or SC* Acute amebic dysentery: Emetine hydrochloride, 1mg/kg daily IM or SC

33. TreatmentTreatment
 Extraintestinal AmebiasisExtraintestinal Amebiasis::
 **Amebic liver abscess, ameboma:Amebic liver abscess, ameboma:
Metronidazole, as above plus dehydroemetine / 10 days orMetronidazole, as above plus dehydroemetine / 10 days or
Metronidazole or dehydroemetine as above plus Chloroquine ,Metronidazole or dehydroemetine as above plus Chloroquine ,
500 mg 2 times daily / 2 days,…..500 mg 2 times daily / 2 days,…..