STUDY OF ENTAMOEBA HISTOLYTICA – Classification and Life Cycle



Phylum :- protozoa
Sub phylum :- Sarcomastigophore
Class :- Rhizopoda
Order :- Lobosa
Genus :- Entamoeba
Species :- histolytica


  • Entamoeba histolytica is worldwide in distribution, but its prevalence is greater in tropics and subtropics than in the temperate zones. It has been reported that incidence of infection is high in Mexico, China, India and parts of South America.

Habits and Habitat

  • Entamoeba histolytica is a microscopic endoparasite of man .it is commonly found in the upper part of the large intestine and is very often lodged in the river, lungs, brain and testes.


  • Entamoeba histolytica is a small microscopic parasitic Amoeba .in its life cycle, it occur in three distinct forms.
  • Trophozoite or magna form.
  • Precystic or minuta form.
  • Cystic forms.


This stage is disease causing.

  • This is growing stage measuring 18 – 30 microns in size.
  • Cytoplasm is divided into clear hyaline ectoplasm and granular endoplasm.
  • A dot shaped karyosome is present in the centre of the nucleus. the nuclear membrane is lined with chromatin granules.
  • Mitochondria are absent an respiratory enzymes are present along the endoplasmic reticulum
  • Nutrition is holozoic and its feeds on the cells of the intestinal wall.

Pre Cystic stage

  1. Trophozoites multiply asexually by binary fission within the wall of large intestine. Some of the daughter cells invade fresh host cells while others become pre cystic or minute forms.
  2. Pre Cystic forms are smaller in size with blunt pseudopodia; endoplasm is free of red blood cells and other ingested food particles.
  3. Nucleus is like the Trophozoite stage.

Cystic stage

  1. In the lumen of the intestine pre cystic or minute forms round up and secrete a tough but flexible cyst wall around them.
  2. The single nucleus in the cyst undergoes two mitotic divisions to form a tetra nucleate cyst.
  3. Tetra nucleate cysts are the infective stage .they pass out with stools.


  • Entamoeba histolytica is found in the colon region of the large intestine as an endo parasite .it can also lodge in the river, lungs, brain and testes.

Symptoms of the disease

  • Entamoeba histolitica causes amoebiasis in man.
  • It invades the mucosa and sub mucosa layers in the large intestine and causes ulcers which later forms abscesses.
  • Blood, mucous, cell debris and swarms of entamoeba are given out with the stool And Trophozites enter the blood circulation and reach liver, lungs, brains and gonads where they erode tissues a forms abscesses which can at a time prove fatal.

Mode of transmission

  • It occurs by ingestion of food or water contaminated with faecal matter Treatment:- Drugs likes Emetine, Vioform, Terramycin and Metronidazole are known to be effective.


  • Hygenic handling of food and water and municipal hygine are necessary to prevent infection by Entamoeba histolytica.

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