Amoebas (yellow) in the brain – but the ensuing immune system overkill is worse (Image: London School of Hygiene and Tropical Medicine/Science Photo Library)

Don’t be too hard on them. Amoebas that weasel their way into our brains and chow down on our grey matter aren’t welcome, but it’s how our immune system reacts that’s really lethal. Setting the story straight could help us deal with them better.

Brain-eating amoebas (Naegleria fowleri) are found in warm freshwater pools around the world, feeding on bacteria. If someone swims in one of these pools and gets water up their nose, the amoeba heads for the brain in search of a meal. Once there, it starts to destroy tissue by ingesting cells and releasing proteins that make other cells disintegrate.

The immune system launches a counter-attack by flooding the brain with immune cells, causing inflammation and swelling. It seldom works: of the 132 people known to have been infected in the US since 1962, only three survived.


Brain-eating amoeba infections are more common elsewhere. “In Pakistan, we have something like 20 deaths per year,” says Abdul Mannan Baig at the Aga Khan University in Karachi.

There is no standard treatment. Doctors in the US have recently started trying to kill the amoebas with miltefosine, a drug known to work on the leishmaniasis parasite. Mannan thinks they should take a different approach, because the immune response may be more damaging than the amoeba itself.

Immune overload

The problem is that enzymes released by the immune cells can also end up destroying brain tissue. And the swelling triggered by the immune system eventually squashes the brainstem, fatally shutting off communication between the body and the brain.

To check their theory, Mannan and his colleagues compared how brain cells in a dish fared against the amoeba with or without help from immune cells. They found that when the immune response was absent, the brain cells survived about 8 hours longer.

In light of this, Mannan suggests that people infected by the amoeba should first be treated with drugs that dampen down the immune system, before getting medicines that target the parasite.

Focal haemorrhage and necrosis in frontal cortex due to Naegleria fowleri (Image: Centers for Disease Control and Prevention)

Jennifer Cope at the US Centers for Disease Control and Prevention in Atlanta, Georgia, thinks the idea is sound. “It is worth testing, but it is very hard to test because the infection is so rare,” she says.

A warming climate could change that, however. Although infection rates haven’t risen significantly since the amoeba was first described 60 years ago, cases are starting to crop up in unexpected places, such as the northern state of Minnesota. “In the US we’ve had our first case linked to drinking water,” says Cope. “We need to track these cases and keep an eye on them.”

In the meantime, Mannan says the brain-eating amoeba deserves a rebranding. He suggests “nose-brain-attacking amoeba” or “olfacto-encephalic amoeba”. “It doesn’t roll off the tongue quite as easily,” says Cope.

Journal reference: Acta Tropica, doi.org/4g4

This article appeared in print under the headline “How brain-eating amoebas really kill”