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Chapter: Microbiology


Amoebiasis is an infection due to E.histolytica


               Amoebiasis is an infection due to E.histolytica


               It occurs only among human and selected primates


               Commonly E.histolytica produce intestinal and extra intesti-nal infections


               Amoebiasis is transmitted by oral ingestion of materials con-taining cyst of E.histolytica


Morphology of the organism

Trophozoites (Figure 22.1)

Entamoeba histolytica and entamoeba coli have both trophozoi-tes and cyst stages. The cytoplasms of E.histolytica is glossy, contains red cells and spherical vacuoles. The nucleus has small central karyo-some and fine regular chromatin granules lining the periphery of nuclear membrane. Entamoeba coli has granular cytoplasm which contains bacteria and other inclusions and ellipsoid vacuoles. Nucleus has ec-centric nucleolus and coarse beaded chromatin at the periphery.



Cysts are round, nuclear morphology is similar to trophozoites. One to four nuclei are seen in E.histolytica and eight nuclei are present in Entamoeba coli cysts.


Clinical manifestations of the disease

               Both intestinal and extra intestinal amoebiasis have an incuba-tion period of more than one week (several weeks)





Asymptomatic Intestinal Infections

               Persons show no symptoms


               They pass cysts in stool


Active Intestinal Disease

               Minority of persons with intestinal infection develop diarrhoeal disease


               They pass red cells and pus in stool


               The symptoms and signs are:


-               Less severe form


Abdominal pain



-               More sever form


Symptoms similar to ulcerative colitis


Secondary intestinal perforations

Toxic mega colon


·              Parasites produce flask- shaped ulcers in which the base is wider than neck at the epithelial surface


·        Organisms are present on the edge of the ulcer


Laboratory Diagnosis


Direct demonstration:

a. Wet mount:


1. Saline – Trophozoites,Cysts


2. Iodine – Cysts


3. LCB - Cysts


b. Stains : Iodine staining


: Iron haematoxylin stain

: Trichrome stain

: Immuno fluorescence staining


c. Culture: non-Axenic andAxenic culture methods are used


Indirect Methods

Epidemiology, Prevention and control

Cysts are ingested through contaminated food and water Flies transfer the cysts from infected stools to food

Control measures consist of improving environmental and food sanitation

Carriers must be barred from food handling

Metronidazole is the drug used for symptomatic amoebiasis

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