Published On: Thu, Apr 10th, 2014

Entamoeba histolytica: New research shows amoeba kills cells by ‘biting’

Research published yesterday in the journal Nature show how the parasitic amoeba, Entamoeba histolytica kills human cells–by amoebic trogocytosis.

According to the paper, researchers say that the amoebae kill by ingesting distinct pieces of living human cells, resulting in intracellular calcium elevation and eventual cell death. After cell killing, amoebae detach and cease ingestion. Ingestion of human cell fragments is required for cell killing, and also contributes to invasion of intestinal tissue.

The internalization of fragments of living human cells is reminiscent of trogocytosis (from Greek trogo, nibble) observed between immune cells, but amoebic trogocytosis differs because it results in death.

“I’ve spent my entire career studying this parasite … and I didn’t realize this was happening,” says study co-author William Petri of the University of Virginia. The amoeba’s brutal modus operandi is “something everyone had completely missed for literally 100 years.”

Researchers have known for more than a century that the amoeba kills human cells, but they weren’t sure how it did the deed. So Petri’s colleague Katherine Ralston examined a mixture of amoebas and human cells under a microscope. Ralston saw that when an amoeba attached to a living cell, the parasite swiftly began gobbling chunks of its victim’s outer covering and innards, inflicting fatal damage. When Ralston added amoebas to a sample of mouse intestines, she saw the parasites nibbling at the intestinal cells before invading the gut tissue. The amoeba “bites” by engulfing a chunk of its victim and pinching it off from the main cell.

E. histolytica is a cause of traveler’s diarrhea is found basically worldwide; however tends to be more common in the tropics and in areas with questionable sanitation and poor nutrition. Africa, Asia and Central and South America is where the majority of illness and deaths tend to occur.



According to the Centers for Disease Control and Prevention (CDC), travelers to developing countries are at low but definite risk for amebiasis.

Data on travelers returning from the developing world were collected from 30 specialized travel or tropical-medicine clinics on six continents. The rate of acute amebic diarrhea ranged from 1.5% in travelers returning from Southeast Asia to 3.6% in those returning from Central America.

In industrialized countries, risk groups include male homosexuals, travelers and recent immigrants, and institutionalized populations.

People mostly get infected with the parasite from ingestion of fecally contaminated food and water containing the amebic cysts. The cysts are pretty resistant to chlorine.

Transmission can also occur through oral-anal contact with a chronically ill or asymptomatic carrier.

Amebiasis is caused by the protozoan parasite Entamoeba histolytica. The parasite may act as a non-pathogenic commensal or can invade tissues and give rise to intestinal and organ disease (rare).

Most infections with E. histolytica are asymptomatic. Intestinal infection can however cause acute and fulminating dysentery which includes fever, chills, bloody and mucoid diarrhea (amebic dysentery).

If the amoeba becomes invasive it can get into the bloodstream and be carried to the liver (most common), lungs or the brain. In these organs they can create abcesses.

The incubation period is typically 2-4 weeks but may be several months or more.

Amebiasis can be diagnosed, though with some difficulty, by finding the characteristic cyst or trophozoites microscopically in stool. It must be differentiated from similar non-pathogenic amoeba.

The nonpathogenic Entamoeba dispar, however, is morphologically identical to E. histolytica, and differentiation must be based on isoenzymatic or immunologic analysis. A good indicator of E. histolytica is if the amoeba demonstrates ingestion of red blood cells.

There are also antibody and antigen detection assays and molecular tests available.

There are several medications available for treating intestinal and extraintestinal amebiasis. See the Medical Letter for treatment options.

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About the Author

- Writer, Co-Founder and Executive Editor of The Global Dispatch. Robert has been covering news in the areas of health, world news and politics for a variety of online news sources. He is also the Editor-in-Chief of the website, Outbreak News Today and hosts the podcast, Outbreak News Interviews on iTunes, Stitcher and Spotify Robert is politically Independent and a born again Christian Follow @bactiman63

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