Here’s how brain-eating amoebas may infect people
Some deadly amoebas may be primed to invade the brain.
Naegleria fowleri, known widely as the brain-eating amoeba, typically dine on bacteria in ponds. But the amoeba’s meal-seeking skills might make it uniquely suited to crawling up people’s noses and into their brains.
Naegleria amoebas are intrepid explorers, probing nooks and crannies in the lab — and they’re persistent, too. When creeping down narrow passageways, the amoebas charge relentlessly forward, almost never turning back, researchers report September 10 in the Proceedings of the National Academy of Sciences. “They’re like robots,” says Lillian Fritz-Laylin, a cell biologist at the University of Massachusetts Amherst. “They just go and go and go.”
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Such persistence might help these tiny, single-celled creatures make the marathon journey from the nostrils all the way to the brain. Fritz-Laylin’s work helps flesh out a largely skeletal picture of Naegleria behavior. “We know almost nothing about the basic biology of these organisms,” she says.
N. fowleri amoebas don’t routinely harm humans. They usually dwell in warm bodies of fresh water, where they squirm through sediment and mind their own business. But on rare occasions, the creatures can be washed up a swimmer’s nose. As the amoebas migrate through the nasal cavity and into the brain, they destroy and eat tissue. Then they begin to reproduce, usually with lethal consequences. The United States typically sees fewer than 10 Naegleria infections each year, often at summer swimming spots, but nearly every one is fatal.
In the lab, Fritz-Laylin’s team tested Naegleria amoebas’ ability to move through different environments. They focused on N. gruberi, a harmless species that shares behaviors with its brain-eating relative. “It’s a lot safer to work with something that can’t kill you,” Fritz-Laylin says.
The researchers placed the amoebas on glass-bottom dishes containing narrow microchannels and watched them move under a microscope. They squeezed through channels smaller than themselves and seemed to be interested in exploring. When the amoebas encountered a channel opening, they very rarely left it, Fritz-Laylin says. Confinement sometimes sped them up, too. Inside the largest channels tested, the amoebas still zipped along twice as fast as cells on the outside.
Naegleria’s persistence and need for speed may make it unique. The team didn’t observe the same behaviors in a different type of amoeba tested. Such attributes probably make Naegleria well-adapted to hunting bacteria in pond sediments, says Fritz-Laylin, who is also a Howard Hughes Medical Institute investigator. But those innocent behaviors could also explain N. fowleri’s dark side. Put one at “the wrong place at the wrong time,” she says, “and it can cause devastating infection.”
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