Life Cycle

When diagnosing amebic infections it is important to separate non-pathogenic species.

< Infection occurs by ingestion of cysts (generally from fecally contaminated food or water)

< Excystation occurs in the ileum of the small intestine

< Trophozoites multiply by binary fission in the large intestine. Most remain in the lumen of the intestine, however, some may invade the intestinal mucosa, enter the bloodstream and develop in extraintestinal sites. Symptoms
Microscopy of Entamoeba histolytica
< Cyst formation is triggered by the dehydration of gut contents in asymptomatic carriers.


Infections of E. histolytica vary in intensity from asymptomatic to severe or fatal invasions.

Asymptomatic infections are responsible for the spread of the parasite with numerous cysts being passed in normal stools.  Diarrheic stools primarily contain trophozoites which cannot persist in the environment.

Invasive forms of the disease lead to amoebic dysentery in which the trophozoites invade the intestinal wall, leading to the formation of amoebic ulcers.  This results in severe diarrhea with blood and mucus present.  In such cases it is important to identify E. histolytica in the stools to differentiate among other causes of dysentery.

If trophozoites penetrate the intestinal wall, serious problems can occur, including liver abcesses, or spread to the lungs and brain, usually resulting in death.

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