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

Last edited and updated on: January 23, 2020 by Sagar Aryal

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.

Morphology

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.

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.

Pathogenesis

• 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

Treatment

• 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.

Prevention

• 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.

References

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