How brain-eating amoebas may reach the human brain

When squeezed through tight spaces, Naegleria amoebas keep pushing ahead

Some deadly amoebas may already be primed to invade the brain.

Naegleria fowleri, widely known as the brain-eating amoeba, usually feeds on bacteria in ponds. But the same food-hunting ability may also make it especially capable of crawling up people’s noses and into the brain.

Naegleria amoebas are determined explorers in the lab, probing every nook and cranny — and they are stubborn, too. When moving through narrow passageways, they press forward relentlessly and almost never turn back, researchers report 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.”

That persistence could help these tiny, single-celled organisms make the long trip from the nostrils to the brain. Fritz-Laylin’s work adds detail to a still sketchy picture of Naegleria behavior. “We know almost nothing about the basic biology of these organisms,” she says.

N. fowleri amoebas do not usually harm people. They generally live in warm freshwater, where they move through sediment and feed on bacteria. But in rare cases, the organisms can be forced up a swimmer’s nose. As they travel through the nasal cavity and into the brain, they destroy and consume tissue. They then begin to multiply, often with fatal results. The United States typically records fewer than 10 Naegleria infections each year, often linked to summer swimming areas, and nearly all are deadly.

In the lab, Fritz-Laylin’s team tested how Naegleria amoebas move through different environments. The researchers 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 team placed the amoebas on glass-bottom dishes with narrow microchannels and watched them under a microscope. The cells squeezed through channels smaller than themselves and appeared eager to explore. Once they found a channel opening, they very rarely left it, Fritz-Laylin says. Confinement sometimes made them faster, too. In the largest channels tested, the amoebas still moved at twice the speed of cells outside.

Naegleria’s persistence and need for speed may make it unusual. The researchers did not see the same behavior in another amoeba type they tested. These traits likely help Naegleria hunt bacteria in pond sediment, says Fritz-Laylin, who is also a Howard Hughes Medical Institute investigator. But those seemingly harmless habits may also explain N. fowleri’s dangerous side. Put one in “the wrong place at the wrong time,” she says, “and it can cause devastating infection.”