This episode is sponsored by Squarespace.

Go to Squarespace.com/microcosmos to save 10% off your first purchase of a website or domain. When you hear the phrase “brain-eating amoebas,” is there a particular image that comes to mind?

Maybe you're conjuring up a malignant blob, one that creeps and eats and creeps some more, its size growing with every chunk it rips out of your brain. Or maybe you're painting a picture of a shape-shifting pacman-like organism bent on terrorizing your body. Or maybe there’s nothing, just, you know, the existential dread that happens when you mash a bunch of seemingly unrelated words together, like “brain-eating” and “amoeba,” only to realize the threat is actually pretty real.

Whatever you envision (or do not), would it be strange to suggest that the notorious brain-eating amoeba that strikes fear in our hearts actually looks something like these little guys? Like tiny little bits of fluff that have just stumbled into your path? Now to be very clear, these are not brain-eating amoebas.

At least, not as far as we know. They belong to the same general group of organisms though called amoeboflagellates. And since we do not, you know, have some brain-eating microbes on hand, we are going to use these amoeboflagellates as sort of a proxy.

As you might guess from the name, amoeboflagellates take all the crawling and shape-shifting blobbiness that we love from amoebas, and combine it with the flagella that powers flagellates. It’s actually a little more complicated than that, and that is why we are focusing on brain-eating amoebas today. Because they have actually been very well-studied, because they impact human life pretty substantially.

In 1961, a 9 year old boy died in South Australia. Four years later, two eight year old girls died as well. They had been healthy, but four days before their death, they reported feeling tired.

The next day, they all had painful headaches along with a fever and other symptoms. Around the same time, a twenty-eight year old man arrived at the hospital with similar symptoms, and died shortly after. These cases were documented by Doctor M.

Fowler, and they were all diagnosed with meningitis, an inflammation of the membranes that protect the brain and spinal cord. Meningitis can be caused by bacterial or viral infections. But when doctors studied the bodies of the patients after their death, they did not find any bacteria or viruses.

They found amoeba. This was a surprise. There are other amoebas that dig their way into human tissues, like Entamoeba histolytica, the parasite behind diseases like amebiasis and amoebic colitis.

But while Entamoeba histolytica can lead to meningitis, it is an intestinal parasite. The organism that killed these patients was something entirely different: a free-living organism, not a parasite, that just happened to find itself in a prime position in a human nasal cavity to kill. The amoeba would later be named Naegleria fowleri for the doctor who first described it.

And it is very important to understand that Naegleria fowleri does not rely on our brains to survive. Members of the Naegleria genus are found around the world in both soil and water. They swim around in lakes and non-chlorinated pools and hot springs.

They can even be found in the nasal passages of humans who are entirely healthy. Ecologically, these amoeba likely play an important role in making sure bacteria populations don’t go out of control by eating them. And some, like Naegleria fowleri, love hot water, which is why they tend to proliferate in the summer.

Naegleria also change up their form depending on the conditions around them. Normally, they exist in their amoeboid form called a trophozoite. But when food is scarce or conditions become unfriendly, they might transition towards their flagellated state.

And if things get very, very bad, then Naegleria pull one of the most popular moves in the microcosmos: they ball up into a protective cyst, putting themselves on pause until things improve and they feel ready to emerge. Imagine Naegleria spending their days swimming around, looking for bacteria, and curling up into cysts when they feel the need for protection… it’s all a bit quaint for a killer amoeba. But perhaps that is Naegleria fowleri’s greatest transformation, the one it embarks on when it goes from water to a human body.

That shift starts when it inadvertently finds itself inhaled into a nasal cavity, usually by someone who has been playing around or swimming in infected water. The nose might not be where the amoeba is intended to be, but assigning intention in the microcosmos is a pointless endeavor. The amoeba has found itself in a new habitat, and so it must adapt.

It begins by sticking itself to the mucus-y surfaces around it. The body does not welcome Naegleria fowleri. Within six hours, the immune system will attempt to mount one of its first lines of defense, using a type of white blood cells called neutrophils to try and control the amoeba.

And over the next few days, the amoeba will continue its path, undeterred by our body’s defenses as it reaches the olfactory bulb. And along its path, Naegleria fowleri will release enzymes that break down the olfactory epithelium it passes by, causing destruction that is felt by the human whose body has become an unwitting home to the amoeba. Now we keep calling this a case of brain-eating amoeba, but the disease itself is actually called primary amoebic meningoencephalitis.

And as we described in the first reported cases, the symptoms are painful. Headaches, vomiting, fatigue, even a coma. Patients usually die within a week of these symptoms.

Now the good news is that these infections are not common. Between 1962 and 2018, there were 45 cases in the US, the country that has reported the most cases. Of course this only accounts for infections that were reported, so there may be more.

The bad news is that survival is exceedingly rare, only around 5% thanks to a drug called amphotericin. But if a treatment exists, then why is survival so rare? Remember that amoebas are not the only organisms that cause meningitis, so narrowing down on Naegleria fowleri as the culprit can be difficult.

And given the rapid destruction of the amoeba, a delayed diagnosis can mean death. So what do we do with that? What do we do with the knowledge that out there in a lake somewhere is an amoeboflagellate capable, with the release of a few proteins and a trip down our nose, of killing us?

I guess we do what we always do. We watch and learn and try to know more about a vast world hiding around us. A world constantly undergoing tiny little transitions between friend and foe.

Or perhaps, more accurately, a world where friend and foe is a dichotomy too harsh to grasp int the myriad relationships in between. Thank you for coming on this journey with us as we explore the unseen world that surrounds us. And thank you to Squarespace for sponsoring this episode.

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It always makes me feel so good to see these names. People who just want to make it possible for us to continue on this journey, which has been a really wonderful part of my life. So thank you so much to all those folks.

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