Amoebiasis

Amoebiasis is caused by E. histolytica.

Common in developing countries: India,

Bangladesh, Pakistan, Nepal.

Risk factors:

Crowded living conditions

Poor sanitation

Mental health Institutions and

Travel to endemic areas.

Amoebiasis

Taxonomic position

Phylum- Sarcomastigophora (motile with

pseudopodia or flagella)

Class – Rhizopoda

Order- Amoebida

Genus – Entamoeba,Endolimax,Iodamoeba,

Dientamoeba

Species

Entamoeba - E. histolitica, E.dispar,

E. hatmani, E. Coli

Endolimax - E. Nana

Iodamoeba - I. butschlii

Dientamoeba – D. fragilis.

Morphology

E. histolytica has two morphological stage:

trophozoite

cyst with an intermediate precyst.

Trophozoite

Size 10 to 60 µm in diameter

Actively motile and invasive form

cytoplasm consists of clear ectoplasm, finely granular endoplasm.

food vacuoles often containing rbc's are common, may contain bacteria.

nucleus has a distinctive central karyosome and a rim of chromatin lining the nuclear membrane

primary habitat is the large intestine but have the ability to metastasize to other organs

Trophozoite

Trophozoite

Entamoeba histolytica trophozoites, two with ingested RBCs.

Cyst

During unfavorable condition, trophozoite condenses into a sphere – the precyst

precyst secretes cyst wall to form the round cyst - 10 to 20 m in diameter

nuclear division begins: Uninucleate cyst Binucleate cyst Quadrinucluate (mature) cyst

chromatoidal bars are present but common in immature cysts.

﴾mature﴿

Important events of life cycle

Host: Man is the only host (definitive).

Infective form: Mature quadrinucleated cyst.

Route of infection: Fecal- oral route.

Site of location: Large intestine.

Pathogenic stage: Trophozoite.

Diagnostic stage: Cyst and Trophozoite.

Life cycleIngestion of quadrinucleated cyst

↓Exystation at small intestine, give rise to eight young

trophozoites (Amebulae)↓

Reside in the lumen of cecum and large intestine↓

Adhere to the epithelial cells and invade↓

Can spread to other organs through blood↓

If condition becomes unfavorable re-encystation occurs and excreted with faeces.

Life cycle

Virulence factors

Galactose and N-acetyl-D-galactosamine –

for binding with colonic mucosa

Motility

Pore forming proteins.

Enzymes – Collagenases, elastase,

hyaluronidas.

Pathogenesis

Infection with E. histolytica can cause:

Asymptomatic infection.

Intestinal amoebiasis.

Extraintestinal disease: hepatic

amoebiasis, pulmonary amoebiasis

Other ectopic sites include: brain, skin,

kidneys, spleen, male and female genitalia

and pericardium.

Pathogenesis

Intestinal amoebiasis: Acute amoebic

dysentery and chronic intestinal amoebiasis.

Acute amoebic dysentery: Occurs over a

period of one to several weeks.

Symptoms: abdominal pain and tenderness,

tenesmus and intermittent diarrhoea,

vomiting and general malaise.

E. histolytica can also cause amoebomas.

Acute amoebic dysentery

Character of ulcers:

Location: May be generalized (Through out the

large gut) or localized to ileo-caecal and sigmoido-

rectal junction.

Size: Pin head to one inch or more.

Shape: Round or oval.

Margin: Flask-shaped.

Base: Filled up by necrotic mass, yellowish or

blackish slough.

Pathogenesis

Hepatic amebiasis –

Trophozoites enter liver via portal vein and

enter the sinusoids – form abscess stay

small or continue to grow

Center of abscess is fill with necrotic fluid

and outer wall full of trophozoites.

If abscess ruptures organisms are available

to eat other organs.

Pathogenesis

Pulmonary amebiasis–

Primary or secondary.

Can enter to lungs via portal circulation or

when liver abscess ruptures through

diaphragm.

Laboratory diagnosis

Principle:

Laboratory diagnosis of intestinal amoebiasis is

based on demonstration of haematophagous

trophozoite, cyst or antigen from stool.

Laboratory diagnosis of hepatic amoebiasis is

practically done by detection of trophozoite from

pus or antigen detection from blood and saliva.

Laboratory diagnosis

Culture: Culture of stool samples followed by

isoenzyme analysis can accurately distinguish E.

histolytica from E. dispar and is considered to be

the 'gold standard' for diagnosis.

However, this method takes several weeks to carry

out and requires special laboratory facilities,

making it impractical for routine laboratory test.

Laboratory diagnosis

Immunological tests:

Antigen detection.

Antibody detection.

Enzyme immunoassays (EIA)

Nucleic acid based technique PCR-based methods.