Entamoeba Histolytica - Cyst, Structure and Life Cycle

Entamoeba,Entamoeba Histolytica,Entamoeba Histolytica Cyst

Entamoeba Histolytica - Cyst, Structure and Life Cycle

Entamoeba Histolytica - Cyst, Structure and Life Cycle

Entamoeba Histolytica is a protozoan found in human body. Under this post, we will read through following topics :

  • Systematic Position of Entamoeba Histolytica
  • Habit and Habitat
  • Structure of Entamoeba Histolytica
  • Life Cycle of Entamoeba Histolytica

Systematic Position of Entamoeba Histolytica

Phylum - protozoa

Subphylum - sarcomastigophora

Class - rhizopodia

Order - amoeboida

Genus - entamoeba

Species - histolytica

Habit and Habitat of Entamoeba Histolytica

Entamoeba histolytica is a microscopic protozoon endoparasite present in human body in the lumen of the intestine.

It is believed to be harmless comensal but sometime it invades the mucosa and submucosa of the intestine wall.

Structure of Entamoeba Histolytica

Entamoeba histolytica is a micro organism belong to Protozoa phylum in human body causing a disease to human referred to as amebiosis.

Amebiosis is one amongst the lot of serious parasitic infections of humans, affecting an estimated 50 million persons worldwide.

Entamoeba Histolytica belongs to rhizopodia class which refers to a single cell organism that divides by binary fission and can replicate in the intestinal tract, primarily in the large intestine or colon.  In the colon the organisms really bore their approach into the visus wall, and cause ulcerations, severe bloody diarrhea called dysentery, and abdominal pain.

It is cosmopolitian in distributin (found across the globe). It is usually found within the tropical and subtropic region and are mainly common on the place wherever sanitation is poor.

Entamoeba histolytica exists in three forms, namely :

  1. Trophozoite/Magna form ( Pathogenic and active stage )
  2. Pre-Cystic Stage/ Minuta Stage
  3. Cystic Stage ( Infective and resting Stage )

1. Trophozoites or magna form    

A. most active and motile.

B. pathogen to man.

C. lives in mucosa and submucosa layer of large intestine of human body.

The unicellular body is composed of following structure :

plasmalimma - The outermost covering of the body is plasmalimma. It is thin elastic and semipermeable membrane.

cytoplasm - the cytoplasm is differentiated into outer clear ectoplasm and central granular endoplasm. the endoplasm contain the nucleus ,food , vacuoles containing the tissue fragment , RBC , WBC and ingested bacteria. contractile vacuole is absent. thus there is no need of osmoregulation.

nucleus - nucleus is small rounded vescular structure. 4-6 micron in size.

pseudopodium -  when entamoeba histolytica moving produce anteriorly a large brood and blunt pseudopodium.

nutrition - the nutition in trophozoit is holozoic, it feeds by phagocytosis. the food particles are ingufest at the posterior end where plasma lemma is more sticky. It feeds mainly upon the blood corpuscles and other host tissue element. It also absorles substances saprozoically from the surrounding medium.

2. Pre Cystic Stage ( Entamoeba Histolytica Cyst )

A. smaller in size as compared to tropozoite stage.

B. encystment happens by forming cyst wall in intestinal lumen.

C. food vacuoles are absent here.

D. ingested food particles and RBC are seen in endoplasm.

3. Cystic Stage ( Entamoeba Histolytica Cyst )

  • 1 to 4 nuclei ( 4 in mature cysts ), uninucleate to quadrinucleate ( mature cyst )
  • Bluntly rounded chromatoidal bars
  • Matured Cyst can sustain twelve days in a cool and moist place and in water for 9 to 30 days.

LIFE CYCLE OF ENTAMOEBA HISTOLYTICA


The Entamoeba histolytica is monogenetic intestinal endoparasite. It complete life cycle only in human being. The life cycle is completed in following steps :

  1. Binary fission
  2. Encystation
  3. Transmission and infection
  4. Excystation
  5. Metacystic development
 
1. Binary fission - Entamoeba histolytica  feeds on the tissue of intestinal wall and multiply asexually by binary fission. The daughter Trophozoites  feed upon the host tissue and again multiply by the binary fission. Some times they stop feeding. Some of them invade fress host cells while while other become in precystic form.

2. Encystation - the precystic form undergoes encystation and secrete a thin and flexible cyst wall around it . The cyst formed at this stage is uninucleate. Soon the nucleus of cyst divide by two mitotic division and form tetranucleate cyst. The tetranucleate cyst is the infective stage.It passes out of  the host in the faeces.

3. Transmission and infection - Infection occur through the intake of contaminated food and water containing tetranucleate cyst. Housefly cockroaches and other insect  feeding faecal matter transfer the infective cyst by their legs and deposits them on unprotected food material.

4. Excystation - In the new host, the ingested cyst pass down the alimentary canal and reach the small intestine. After 5 to 6 hours the cyst wall digested by trypsin in small intestine. The released tetranucleate entamoeba is called metacyst.

5. Metacystic development - Each metacyst divide by binary fission. Its nuclii divide and produce 8 small uninucleate metacystic trophozoites. These trophozoites pass into the large intestine,penetrate the mucas lining and grow into mature trophozoites and produce amoebic dysentery or amebiasis disease.

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