Parasite Kills Human Cells and Wears Their Remains As Disguise
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For decades scientists have been puzzled by a tiny parasite that affects millions worldwide, with the power to liquefy human organs and evade the immune system in ways that science hasn't been able to explain.
Now University of California, Davis microbiologist professor Katherine Ralston and her team, have uncovered its terrifying secret.
Entamoeba histolytica has the unusual ability to kill human cells and then wear them as a disguise to escape the immune defenses.
The research, the teams said, could pave the way for new treatments to stop the parasite once and for all.
Image shared on the UCDAVIS website shows E. histolytica (green) attacking human T-cells (white blood cells).
Image shared on the UCDAVIS website shows E. histolytica (green) attacking human T-cells (white blood cells).
Katherine Ralston
What Is Entamoeba histolytica?
Entamoeba histolytica is a single-celled parasite infects around 50 million people each year and claims some 70,000 lives annually.
Mostly encountered in developing countries with poor water sanitation, the shape-shifting amoeba typically enters a person's colon after ingesting contaminated food or water.
While, in most cases, such an infection causes nothing worse than diarrhea, they can sometimes become deadly.
Once inside the body, it chews in ulcers inside the colon, liquefying parts of the liver and invading the brain and lungs.
In developed countries like America, Entamoeba histolytica infections are rare, although they still account for at least five deaths per year. The parasite is usually brought into the U.S. by individuals who have picked up an infection abroad.
How Entamoeba histolytica Operates
Scientists used to believe that the parasite injected poison into human cells to kill them, but Ralston's research revealed a very different process.
Back in 2011, during her postdoctoral fellowship at the University of Virginia, Ralston observed the parasite under a microscope and found that it was actually taking bites out of human cells.
In a series of later studies, she discovered that this amoeba kills cells through a process called "trogocytosis"; after it's done chewing on human cells, it wears the remains as a disguise to trick the immune system into not fighting it.
What the Study Showed
While researchers have struggled to study this parasite effectively because of its massive genome, Ralston and her team have drafted an "RNAi library" that allows them to study each one of the parasite's 8,734 known genes to understand how it operates.
Using a gene-editing tool known as CRISPR, Ralston and her team aim to label proteins within the parasite with fluorescent markers. This should allow them to observe the interactions of said protiens under a microscope.
Gene editing may also allow to team to delete small parts of Entamoeba histolytica's genes and proteins to find which are crucial and how they could be targeted with drugs.
"We now see a light at the end of the tunnel, and we think this could be achievable," said study author and UC Davis biochemist Wesley Huang.
Do you have a tip on a health story that Newsweek should be covering? Do you have a question about parasites? Let us know via science@newsweek.com.
References
Bettadapur, A., Hunter, S. S., Suleiman, R. L., Ruyechan, M. C., Huang, W., Barbieri, C. G., Miller, H. W., Tam, T. S. Y., Settles, M. L., & Ralston, K. S. (2021). Establishment of quantitative RNAi-based forward genetics in Entamoeba histolytica and identification of genes required for growth. PLOS Pathogens, 17(11). https://doi.org/10.1371/journal.ppat.1010088
Huang, W., Ruyechan, M. C., & Ralston, K. S. (2025). Work with me here: Variations in genome content and emerging genetic tools in Entamoeba histolytica. Trends in Parasitology, 41(5), 401–415. https://doi.org/10.1016/j.pt.2025.03.010
Miller, H. W., Tam, T. S. Y., & Ralston, K. S. (2022). Entamoeba histolytica Develops Resistance to Complement Deposition and Lysis after Acquisition of Human Complement-Regulatory Proteins through Trogocytosis. mBio, 13(2). https://doi.org/10.1128/mbio.03163-21
Ralston, K. S., Solga, M. D., Mackey-Lawrence, N. M., Somlata, Bhattacharya, A., & Petri, W. A. (2014). Trogocytosis by Entamoeba histolytica contributes to cell killing and tissue invasion. Nature, 508(7497), 526–530. https://doi.org/10.1038/nature13242
Ruyechan, M. C., Huang, W., & Ralston, K. S. (2024). Cross-species protection suggests Entamoeba histolytica trogocytosis enables complement resistance through the transfer of negative regulators of complement activation (p. 2024.10.04.616735). bioRxiv. https://doi.org/10.1101/2024.10.04.616735
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