The Ferocity of Amoebae at the Microscopic Level

An amoeba (in green) is eating a human cell (in pink).
Courtesy: Katy Ralston; http://www.npr.org/blogs

        We've all heard the headlines detailing fateful encounters with a dreadful foe, the amoeba. An amoeba is a single-celled organism that can infect a host and cause serious illness, sometimes to the point of death. Amoeba infections tend to be rare, but their effects can be damaging. For example, Naegleria fowleri, an amoeba that is commonly found outdoors in untreated water, can infect humans through the nose. Remarkably, 90% of infected individuals are asymptomatic, but inflammation of the brain can develop in the few cases that do present symptoms. Scientists discovered that this amoeba secretes enzymes that digest brain tissue, which the amoeba then utilizes as sustenance.
         If this occurrence sounds like the makings of a horror film, this is just the tip of the iceberg. Another subtype of amoeba, called Entamoeba histolytica, populates the intestine upon infection and results in severe cases of food poisoning. The mechanism by which E. histolytica causes disease has remained unclear until now. A recent report in Nature describes the methods utilized by this amoeba to antagonize human cells. Dr. William Petri's group at the University of Virginia uncovered the devastating events by imaging E. histolytica activity under a microscope. To the groups' amazement, the amoeba chewed on human cells and regurgitated the cellular debris. Upon making this observation, Petri's group was perplexed. Why would the amoeba destroy human cells in this manner without digesting their material? Their hypothesis states that the amoeba is solely attempting to break through the intestinal wall, rather than consuming intestinal cells. With this revelation, Petri hopes new tactics can be developed to combat the cellular carnage that E. histolytica and similar amoebae  inflict.
        It is common to observe bacteria and other parasites exhibiting aggressive behavior toward each other, but to visualize an amoeba eating a human cell and merely spitting out the remnants evokes a different sense of fear. We like to consider ourselves near the top of the food chain, so to see a microscopic organism challenge that notion is difficult to accept. This story reminds us that vigilance is essential to remaining in good health. So don't forget to boil that water for your neti pot and remember to wash food items in clean water!