Entamoeba histolytica parasites ingesting bites of intestinal cells in a mouse intestine, captured using live two-photon microscopy. Tissue was from a mouse expressing membrane-targeted green fluorescent protein (green) and amoebae were coloured blue.
Researchers have found a  parasitic amoeba that kills human cells in a unique way – by nibbling them. Entamoeba histolytica causes a potentially fatal diarrhea common in the developing world, infecting up to a third of children in some areas. The team were stunned to discover it kills by taking small bites of the cell until it dies – and then losing all interest in eating the remaining corpse.

Entamoeba histolytica causes a potentially fatal diarrhea common in the developing world. Approximately a third of all infants are infected within their first year of life in the Bangladeshi slum where the U.Va. researchers have been working.  The amoebae colonize the colon and begin their nasty work, which can produce diarrhea, inflammation of the colon, bowel diseases – or even no symptoms at all. Scientists at the University of Virginia School of Medicine discovered the previously unknown way to kill human cells – which they say is exactly how a piranha might attack its prey.

Entamoeba histolytica parasites ingesting bites of human Jurkat T cells, captured using live confocal video microscopy. The cell membranes of the human cells were pre-labeled with DiD (pink) and the amoebae were pre-labeled with cell tracker green (green).Until now, researchers had assumed that the amoeba, Entamoeba histolytica, killed and then engulfed and consumed human cells.  But the team found the amoeba takes small bites of the cell until the cell dies – and then the amoeba loses all interest in eating the corpse. ‘This is the first demonstration that nibbling can serve as a way to kill other cells,’ Katherine Ralston, who led the research, said.  ‘The findings suggest that amoebae might invade and destroy host intestinal tissue by nibbling alive the cells that line the gut. Intriguingly, there are hints that organisms can also nibble.  ‘Perhaps this process is more common than we realize, and it is taken to the extreme in the case of the amoebae, which use nibbling to kill.’ Approximately a third of all infants are infected with the bug their first year of life in the Bangladeshi slum where the researchers have been working.  The amoebae colonize the colon and begin their nasty work, which can produce diarrhea, inflammation of the colon, bowel diseases – or even no symptoms at all. Rather than poisoning human cells, as has been previously thought, the amoebae appear to nip at the cellular membrane, as a goldfish might nip at another goldfish.  Eventually, the amoeba consumes enough of the membrane – the cell’s casing – that the membrane becomes unstable and the cell dies.  The amoeba then detaches itself from its dinner and moves on to another, still-living meal. More