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Amebiasis
(Amebic Dysentery)
Dr. M.H.ANVARI
Amebiasis
(Amebic Dysentery)
Causal agent: Entamoeba histolytica is well recognized
as a pathogenic amoeba.
History: Loosh was first described in 1875
Geographic Distribution: Worldwide, with higher
incidence of amebiasis in developing countries.
In industrialized countries, risk groups include male
homosexuals, travelers and recent immigrants, and
institutionalized populations.
Morphology

Different form of E. histolytica;

1- trophozoite

2- precyst

3- cyst(1, 2, 4 nuclei)
Trophozoite chractere



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:

invasive form
Non-invasive form
Different form of E.histolytica cyst
Life cycle
Life cycle
Epidemiology

Prevalence of amebic infection varies with level of sanitation
and generally higher in tropics and subtropics than in
tempearate climates.

*Worldwide prevalence is about 10% to 50%
*Cyst passers are important source of infection



The true estimated prevalence of E. histolytica is close to 1%
worldwide.
Entamoeba histolytica is the second leading cause of
mortality due to parasitic disease in humans. (The first being
malaria). Amebiasis is the cause of an estimated 50,000100,000 deaths each year.
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
Pathogenesis

Effective factores:
 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)
Pathogenicity mechanisms

1- secreting proteolytic enzymes( histolysine )
and cytotoxic substances.

2 - contact-dependent cell killing

3 – cytophagocytosis

Amebic killing target cell:


1- receptore-mediated adherence of amebae to target cell ( adherence
lectin)
2- amebic cytolysis of target cell

3- amebic phagocytosis of killed target cell
Clinical symptoms
Asymptomatic infection
Symptomatic infection
Intestinal Amebiasis
Dysenteric
Non-Dysenteric colitis
Extraintestinal Amebiasis
Hepatic
Liver abscces
Pulmonary
The extra foci
Acut nonsupprative
Intestinal Amebiasis symptoms: Diarrhea or dysentery, abdominal pain, cramping , anorexia,
weight loss, chronic fatigue
Pathology of Amebiasis
Flask-like Ulcer
Extra-ntestinalAmebiasis
Pyogenic- Liver Abscess
Liver abscess
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.
Diagnosis


Paraclinical Diagnosis:
Sigmoidoscopic examination:
precence of a grossly normal mucosa between the ulcers serves to
differentiate amebic from bacillary dysentery,( the entire mucosa being
involvoed in bacillary dysentery).


Hepatomegally
C.B.C. : leukocytosis in Amebic dys. rises above 12000 per microliter,
but counts may reach 16000 to 20000 per microliter.
Laboratory Diagnosis

Entamoeba histolytica must be differentiated from other intestinal
protozoa including: E. coli, E. hartmanni, E. dispare,……

Differentiation is possible, but not always easy, based on morphologic
characteristics of the cysts and trophozoites.

The nonpathogenic Entamoeba dispar, however, is morphologically
identical to E. histolytica, and differentiation must be based on
isoenzymatic or immunologic analysis.

Molecular methods are also useful in distinguishing between E.
histolytica and E. dispar and can also be used to identify E.
polecki.
Microscopy
Microscopic identification
This can be accomplished using:


Fresh stool: wet mounts and permanently stained preparations
(e.g., trichrome).

Concentrates from fresh stool: wet mounts, with or without
iodine stain, and permanently stained preparations (e.g.,
trichrome).
Trophozoites of Entamoeba histolytica /E.
dispar ( trichrome stain )
Microscopy
B
A
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 .
Trophozoites of Entamoeba histolytica with ingested
erythrocytes (trichrome stain)
E
F
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 .
Cysts of Entamoeba histolytica
/E. dispar

GHI
H
I
Cysts of Entamoeba histolytica/E.
dispar ,permanent preparations stained
with trichrome.
Immunodiagnosis
(Antibody Detection)

1- Antibody detection

2- Antigen detection may be useful as an adjunct to
microscopic diagnosis

The indirect hemagglutination (IHA)

The EIA test detects antibody specific for E. histolytica in
approximately 95% of patients with extraintestinal amebiasis,
70% of patients with active intestinal infection, and 10% of
asymptomatic persons who are passing cysts of E. histolytica.
Antigen Detection
Antigen detection may be useful as an adjunct to microscopic
diagnosis in detecting parasites and to distinguish between
pathogenic and nonpathogenic infections.
Recent studies indicate improved sensitivity and specificity of
fecal antigen assays with the use of monoclonal antibodies
which can distinguish between E. histolytica and E. dispar
infections .
Molecular diagnosis

In reference diagnosis laboratories, PCR is the
method of choice for discriminating between
the pathogenic species (E. histolytica) from the
(nonpathogenic species( E. dispar.
Treatment
Intestinal Amebiasis:
 *Asymptomatic amebiasis(cyst passer): Diloxanide furoate (

furamide)
500 mg 3 times daily / 10 days

*Symptomatic amebiasis ( troph. & cyst): - Iodoquinol , 650 mg 3
times daily/ 20 days or Metronidazole (Flagyl) , 750 mg 3 times daily/ 10
days

*Amebic colitis: Chloroquine, 250 mg 2 times daily

* Acute amebic dysentery: Emetine hydrochloride, 1mg/kg daily IM or SC
Treatment

Extraintestinal Amebiasis:
 *Amebic liver abscess, ameboma:
Metronidazole, as above plus dehydroemetine / 10 days or
Metronidazole or dehydroemetine as above plus Chloroquine ,
500 mg 2 times daily / 2 days,…..