Entamoeba histolytica- Morphology, Epidemiology, Life cycle, Pathogenesis, Clinical findings

Entamoeba histolytica– Morphology, Epidemiology, Life cycle, Pathogenesis, Clinical findings

  • 500 Million populations are infected over the world.
  • 60-70% population in Pakistan is infected
  • Entamoeba histolytica caused amebic dysentery and liver abscess.


  1. Trophozoites
  2. A cyst (egg)
  • Cyst= it is immovable and has disease-causing form.
  • Cyst survives for a long period of time because it is double layered.
  • Trophozite= they are motile and have a small shelf life so they cannot survive outside.
  • Encystment (trophozoite –> cyst)
  • Excystment (cyst –> trophozoite.

Transmission and Epidemiology

  • Transmitted by the fecal-oral route.
  • 5-F are the main source of transmission that includes:
    • Finger (contaminated hands)
    • Fomites (public places, door handles)
    • Fly
    • Feaces
    • Food
  • 70-80% are transmitted via 5F or fecal-oral route
  • Reaming 10-20% are transmitted by blood e.g. malaria, leishmania
  • Infection by Entameba histolytica occur globally, but mostly in tropical countries due to poor sanitation, more infection will be there due to this reason.
  • About 1% to 2% of people are affected in the United States.
  • Infection is common in homosexuals means having anal sex.

Entameoba histolytica- Morphology, Epidemiology, Life cycle, Pathogenesis, Clinical findings

Image Source: Your Article Library and CDC

Life cycle

  • The cyst wall is resistant to gastric juice.
  • Then Cyst reach to caecum or lower part of ileum due to alkaline medium
  • Cyst wall damage by trypsin and lead to exystation.
  • Metacystic trophozoites.
  • Trophozoites in the colon (sometimes invade to blood & then to liver, brain, and lungs.
  • Cyst 1-4 nuclei.
  • Passed in feces.
  • Cyst in contaminated food and water.
  • Cyst ingested.
  • Metacyst in the small intestine.


  • Organism are entering into the host in the form of a cyst, which is transmitted through the fecal-oral route from contaminated water and food.
  • Anal oral (male homosexuals) transmission also occurs.
  • No animal reservoir
  • In the ileum, the ingested cyst is differentiated into trophozoites
  • But colonization in caecum and colon.
  • After that trophozoite enters into colonic epithelium and secretion of enzyme takes place as a result of localized necrosis occur.
  • Inflammation also is there.
  • Lesions, when reached to mucosal layer flask-shaped ulcer, occur
  • Much of the Intestine is damaged.
  • Invasion of the portal circulation takes place in all of these results.

Clinical finding

  • Flask shaped ulceration in the colon
  • Abdominal pain
  • Diarrhea
  • Vomiting
  • Amoebic dysentery (blood & mucus in the stool)

Extraintestinal amoebiasis

  • Hepatic amoebiasis

Transmit via portal vein from the intestine to the liver and caused liver inflammation after that infects diaphragm which leads to pulmonary amoebiasis that infects lungs.

  • Cerebral amoebiasis

Transmitted from lever to heart and then move toward the brain to develop cerebral lesion.

Mild symptoms

  • Diarrhea including pus and painful passages of stool.
  • Stomach pain
  • Nausea
  • Stomach cramps

Severe symptom

  • Amoebic dysentery
  • Profuse diarrhea
  • Liver abscess
  • Severe ulceration
  • Colitis
  • Megacolon ameboma


  • The choice of treatment for symptomatic intestinal amebiasis or hepatic abscesses is metronidazole (Flagel)
  • Trinidazole
  • There should be no need to drained hepatic abscesses.
  • Iodoquinol or paromomycin should be used for the treatment of asymptomatic cyst.


  • Avoid fecal contamination of food and water.
  • Used good personal hygiene such as handwashing
  • Municipal water supplies are also purified
  • The human feces (night Soil) should not be used as a fertilizer in crops.
  • Used cooked vegetables in endemic areas.


  1. https://www.healio.com/infectious-disease/gastrointestinal-infections/news/print/infectious-disease-news/%7Bc4864d2e-afa4-4f19-a159-81305359dc9c%7D/e-histolytica–a-formidable-gastrointestinal-infection
  2. https://www.hindawi.com/journals/cjgh/2018/4601420/
  3. https://emedicine.medscape.com/article/212029-overview
  4. https://www.emedicinehealth.com/amebiasis_entamoeba_histolytica_infection/article_em.htm
  5. https://www.cdc.gov/dpdx/amebiasis/index.html
  6. https://www.medicinenet.com/amebiasis_entamoeba_histolytica_infection/article.htm
  7. https://www.infectiousdiseaseadvisor.com/home/decision-support-in-medicine/infectious-diseases/entamoeba/
  8. https://www.britannica.com/science/Entamoeba-histolytica

Entamoeba histolytica– Morphology, Epidemiology, Life cycle, Pathogenesis, Clinical findings

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