Entamoeba histolytica

Mrs. Dalia Kamal EldienMsc in Microbiology

Lecture NO (3)

Objective Revision for amoebaMain species for medically important Introduction to E .histolyticaModes of Transmission Morphology of cyst, trophozoite & precystLife cyclePathology of amoebic dysenteryLaboratory diagnosisTreatment& control of infection

Introduction

AmoebaAmoebae consist of a shapeless mass of moving

cytoplasm which is divided into granular endoplasm and clear ectoplasm.

They move by pushing out the ectoplasm to form pseudopodia (false feet) into which the endoplasm then following it.

Amoeba reproduce asexually by simply dividing into two cells (binary fission).

Main species• According to the pathogenicity, they classified in to two

groups, pathogenic and non pathogenic

Pathogenic • Entameboa histolytica

Non pathogenic

• Entameboa coli• Endolimax nana• Entameboa hartmanni• Entameboa dispar

Entameboa histolytica

A world-wide distribution, with a higher prevalence in tropical and subtropical countries, 10 % of the world population carries the parasite.

Entameboa histolytica lives in the intestine as a trophozoite, i.e. vegetative stage of protozoa showing motility and the ability to grow, feed, and reproduce.

It produces resistant cysts by which it is transmitted to other people (infective stage).

Disease Entameboa histolytica cause Amoebiasis or amoebic

dysentery, occurs when E. histolytica trophozoites invade the wall of the large intestine and multiply in the submucosa, forming large flask-shaped ulcers.

The amoebae ingest red cells from damaged capillaries.Compared with bacillary dysentery, the onset of amoebic

dysentery is less acute, lasts longer, and there is usually no significant fever.

Modes of Transmission

By ingestion of contaminated food or water with amoebae cyst (infective stage).

Oral fecal contamination (children).House flies and cockroaches

Incubation period:1 - 14 days with often sudden onset.

Morphology

1- Trophozoite:

– It is 10-20μm, present in large intestine.

o Ectoplasm: well defined hyaline layer.

o Endoplasm: granular cytoplasm

o Nucleus: 3.7μm, spherical, central, small karyosome and fine

peripheral chromatin dots.

Trophozoite acts as active motile feeding reproducing stage.

E. histolytica trophozoite with ingested red blood cell

2-Precyst: Trophozoite withdraws its pseudopodia and

becomes rounded and devoid of food inclusions.

3- Cyst: 10-18 μm, nucleus divides twice by mitotic division to

form 4 nucleated cyst (infective stage).

Life cycleCysts ingested in food, water or from hands contaminated

with faeces.Cysts excyst in the small intestine, forming trophozoite,

which pass and multiply in large intestine. Trophozoites encyst. Infective cysts passed in faeces.Faeces containing infective cysts contaminate the

environment.

Life cycle

1- Intestinal amoebiasis:-o Invasion of the intestinal wall leads to formation of

several flask-shaped ulcers in the colon as primary lesions.

2- Extra-intestinal amoebiasis:o The lesions are secondary to the primary large

intestinal lesions and may result in hepatic, pulmonary or cerebral, renal....ect amoebic abscess.

Pathology

Clinical manifestations

Infections of E. histolytica vary in intensity from asymptomatic to severe or fatal invasions.

Asymptomatic infections are responsible for the spread of the parasite with numerous cysts being passed in normal stools.  Diarrheic stools primarily contain trophozoites which cannot persist in the environment.

Invasive forms of the disease lead to amoebic dysentery in which the trophozoites invade the intestinal wall, leading to the formation of amoebic ulcers.  This results in severe diarrhea with blood and mucus present.  In such cases it is important to identify E. histolytica in the stools to differentiate among other causes of dysentery.

Laboratory diagnosis

1) Diagnosis of intestinal amoebiasis:a) Stool examination: cyst is found in formed stool,

trophozoite in diarrheic stool. Both forms may be found in soft stools. Examination must be carried out immediately because most trophozoites die in less than 30 minutes.

b) Culture: Culture on specific media may be used to increases the number of predicted positive cases. Lock- egg slant medium (L.E.S), this medium is used for culturing the E. histolytica in clinical specimens.

E.histoltica cyst in normal saline preparation

E.histoltica cyst in iodine preparation

E.histoltica trophozoite

Cyst vs trophozoite

Cyst & trophozoite in same slide

c) Sigmoidoscopy and biopsy: In mild cases there are usually no findings. However, characteristic amoebic lesions may be found in severe cases.

d) Serology: Many tests are available, but their use for diagnosis of intestinal amoebiasis is limited because antibody develops only after a significant degree of tissue invasion. Asymptomatic cysts carriers have negative serologic tests, unless tests are positive from previous invasive amoebiasis.

2) Diagnosis of extra-intestinal amoebiasis:

a) Serology: More than 90% of patients have positive

serologic titers.

b) Radiology: May be suggestive specially in hepatic

amoebic abscess.

c) Detecting the parasite: Aspiration of the lesion in

selected cases may be of help.

TreatmentThe drug of choice for intestinal amoebiasis, is

Metronidazole (Flagyl) 5 - 10 daysThe Side effects; headache, nausea, diarrhea, altered

sense of smell

Infection Control

1) Treatment of infected cases.

2) Flies control.

3) Food handlers examination.

4) Health education.