In 2023, both a toddler in Arkansas and a swimmer in Texas died from the infection of a brain-eating amoeba, Naegleria fowleri, likely contracted from local water sources. “Brain-eating amoebas” is a scary headline that sounds like something out of the Twilight Zone, but just how worried should we be? And how serious are the ramifications of infection? (Spoiler: They’re pretty darn serious.)
On this episode of Heath Matters, we sit down with Dr. Bobbi Pritt to talk about brain-eating amoebas, what they are, how concerned we should be about them, and ways to avoid infection.
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Read the transcript:
Kristen Meinzer:
Welcome to “Health Matters,” a podcast from Mayo Clinic where we discuss the latest medical advice, news, and research to help you live a happier and healthier life. My name is Kristen Meinzer. I’m a writer and journalist. For this episode, we’re talking about the brain eating amoeba.
It may sound like the premise of a campy sci-fi horror movie, but they are real. Infection comes with a terrifyingly high death rate: 97%. These microscopic zombie-wannabes, scientifically known as naegleria fowleri (nay-glee-ree-uh fau-lr-eye), live in freshwater and soil all over North America.
Luckily, infection rates are quite low. Over the last ten years, there have been only 29 reported cases in the U.S. To put that number in perspective, over that same time period, over 40,000 people died from accidental drowning. Which, itself, is quite rare. So, statistically, not something to lose sleep over, but it’s still a good idea to be aware of what actions might put you at a higher risk of infection and how to stay safe while enjoying your favorite warm weather activities.
To help guide us through the risks and precautions, we’re talking to Dr. Bobbi Pritt, a microbiologist and pathologist who focuses on clinical parasitology, vector-borne diseases, and the pathology of infectious diseases.
Dr. Pritt, thank you for joining us!
Dr. Pritt:
Thank you. It’s so great to be here.
Kristen Meinzer:
Can you just, first of all, explain what we’re talking about when we talk about brain eating amoebas?
Dr. Pritt:
Sure. It’s a scary term and it’s a scary disease. What we’re talking about is an infection where amoeba, those are free living organisms that normally have nothing to do with us, get into our bodies in rare situations, go to the brain and cause usually fatal disease.
Kristen Meinzer:
Before we all freak out about this.
Dr. Pritt:
Yes.
Kristen Meinzer:
How common is this infection?
Dr. Pritt:
The good news is, it’s pretty rare, there’s only a few cases reported in the United States each year, and in fact, the Centers for Disease Control and Prevention, the CDC, they did a study looking between 1962 and 2022, where there were only 157 reported cases. That’s the good news, despite that this is a terrible infection and that most people do die if they get it.
Kristen Meinzer:
Now, how do they get it?
Dr. Pritt:
They get it usually by swimming in water that is contaminated with this free living organism, Naegleria fowleri. They can also get it when water goes up their nose in other activities. Essentially, water containing the organism, this amoeba, has to get up into the nose, and then from there, it attracts to our olfactory nerve and it tracks along those nerves directly into the brain. There it literally does eat your brain tissue. So it is a brain eating amoeba and causes swelling and death.
Kristen Meinzer:
That’s terrifying. What distinguishes this particular amoeba from other amoebas, or is this just any amoeba that can do this to us?
Dr. Pritt:
No, thankfully it is only this one species called Naegleria fowleri. Let’s start with just talking about what amoebae are. An amoeba is singular, amoebae is plural. These are organisms that are single celled. They’re microscopic. You can’t see it with the naked eye. You need a microscope. They move by extending these finger-like projections into the environment. These little projections are called pseudopods.
That’s actually not just how it moves, but also how it eats. It engulfs organisms with these little finger-like projections and then ingests the organism, usually a bacterium or an algae or a yeast into its body and then digests it. They also have a very simple form of reproduction. They essentially just divide. You end up with one organism. It divides into two by a form of asexual reproduction called binary fission.
In fact, if you look at the Tree of Life, and how bacteria and viruses and other organisms are related to one another, you’ll find amoebae on the same branch as humans and other animals. It’s very different from an evolutionary standpoint compared to bacteria, for example.
Kristen Meinzer:
Amoeba are kind like great grandparents. They’re back in the tree.
Dr. Pritt:
They’re definitely an early stage of a single celled eukaryotic organism. But of course, they’ve been evolving for the millennia, just like we have. Whatever distant ancestor we had is something probably long since gone, and we’ve all moved on in different pathways since then.
Now, let’s get to this specific amoeba, Naegleria fowleri. This is an amoeba that is free living. There are many different types of amoebae, but this particular one is in the environment. In fact, you might have seen it if you did one of those experiments in school and in science class, where you take a drop of pond water and look at it under a microscope, and usually it’s eating bacteria in the environment. But as we said, in some situations, it can get up into the nose, where it then sees that as a gateway into the body, directly to the brain.
Now, Naegleria fowleri is the only species of Naegleria that can infect humans. Then there are a couple of other types of amoeba that can infect humans and go to the brain, but they’re all pretty rare.
Kristen Meinzer:
I did, in fact, in school, look under the microscope and look at that pond water. I think a lot of Minnesota kids did that. I did that growing up in Minnesota, but is that exclusively where they live? Places like ponds and freshwater? Can they actually come out of places like the tap of my kitchen sink? Where can I find these?
Dr. Pritt:
Yes. Usually it’s freshwater. They’re a natural part of our environment and they’re found on every continent across the world except Antarctica. That’s because they’re thermophilic. They like warm temperatures. Antarctica is just too cold. Usually they’re found in freshwater. They can survive a little bit in brackish water, but you won’t find them in really salty seawater. Now you asked the question about your tap. In situations where the water is not completely chlorinated, then yes, they could potentially be in your tap water.
If you have a well, or if you have municipal water supply feeding your tap, but it’s an old system and perhaps the pipes are very long from the point where the water is purified, yes. There have been some rare instances where there’s not enough chlorine in the water by the time it finally reaches your tap. That is, again, very uncommon, but I think that all people should just be safe and consider that the water that’s around them may have amoeba in it.
Kristen Meinzer:
That’s why we’re all told to boil our water before we use a neti pot, right?
Dr. Pritt:
Yes, absolutely. We’ve talked about how this organism gets into the body. It’s through the nose. You can’t get it from drinking. It doesn’t come in through the mouth. It can’t be transmitted person to person. It has to pretty forcibly get up the nose all the way up to the very top of the nose where the nasal sinuses are. That’s where your olfactory nerves, the nerves that allow you to smell, reach into the top of the nasal cavity and then track back to the brain. That’s how you get the sensations to your brain that you sense as smell. Those Theileria are what the amoebae use as a little highway directly to your brain.
Kristen Meinzer:
But, okay, you said these Naegleria, for the most part, they’re eating things like fungi and bacteria and so on. Why would they be eating my brain? No!
Dr. Pritt:
They’re not discriminating. They don’t usually live in our bodies, but like I said, sometimes they happen to get into our bodies and then they just see different types of food sources and they can take advantage of them.
Kristen Meinzer:
No!
Dr. Pritt:
I know. Scary and horrifying.
Kristen Meinzer:
It is. Let’s talk a little bit about how common you said they are on every continent. They’re all over the world except in Antarctica. Are they? I mean, is there a number per liter? Are there billions of them in every tablespoon of water? How many are there?
Dr. Pritt:
Well, it’s variable. We think the organisms are found mostly down in the sediment in the bottom of your freshwater pond or lake. That’s why one of the recommendations is to avoid really kicking up the sediment.
We also know that they love warm water. The warmer it is, the more they’re going to multiply. On a hot summer day, if your lake levels are low and you’re swimming around and kicking up all the sediment, that could result in a very high concentration of Naegleria in the water.
Kristen Meinzer:
You’ve mentioned a few temperatures here. Is there an ideal temperature that the water is when Naegleria are most thriving?
Dr. Pritt:
Studies have shown that. It really starts proliferating around about 86 degrees Fahrenheit. Pretty warm. It thrives in a range of around 93 to 113 degrees Fahrenheit.
Kristen Meinzer:
That’s my body temperature.
Dr. Pritt:
Yeah, it can actually survive up to 157 degrees Fahrenheit. It can survive in hot springs. That’s why if you go to hot springs, you’ll sometimes see signs that say, don’t put your head under the water.
Kristen Meinzer:
Oh.
Dr. Pritt:
There’s a lot of Naegleria proliferating and hanging out in those hot springs.
Kristen Meinzer:
Okay. Got it. Talk about how much water we’re limited to have in a neti pot. When I get sick I do a cup and a half for each nostril. Is that roughly how much water is going up someone’s nose before they get a Naegleria in them? Or could it be less than that? More than that?
Dr. Pritt:
It probably could be less than that, but no one really knows. What we do know is that people are at risk when they are getting water forcefully up their nose, think kids jumping, doing cannonballs into the lake, but no one’s actually measuring how much water went up their nose.
Neti pots, that’s more of a defined volume of water, but there may not be a lot of Naegleria in that particular neti pot, but you could imagine that if you even just get a little bit of water that’s teeming with Naegleria, then that, a smaller volume might also do the trick. I really would say that there’s no safe amount of water to get up your nose.
Kristen Meinzer:
Naegleria fowleri, a wiggly little critter, squished into a single cell, hanging out in pretty much every body of freshwater. Just blobbing its way through the dirt at the bottom of a lake or stream, looking for snacks.
Once in a blue moon, they find themselves cruising along the nasal express, traveling up an olfactory nerve to end up in a veritable Naegleric paradise, where it’s always the perfect temperature and there’s a bounty of delicious food in every direction. Food which happens to be your brain. Good news for the amoeba, bad news for you. Because pretty much anytime this happens, the human dies, and rather quickly. Let’s talk about why.
Kristen Meinzer:
Let’s say a Naegleria does get up my nose. How fast is it moving from my nose into my brain?
Dr. Pritt:
It’s pretty quick. That’s our area of interest. It’s within days that the organism would enter your brain and really start doing damage, eating brain tissue, causing inflammation. Your body tries to protect itself and recruits inflammatory cells. You start getting a lot of swelling and damage, and those days, usually within about two weeks, people are dead.
Kristen Meinzer:
When do people actually start showing symptoms and feel like something’s not right?
Dr. Pritt:
Yeah, the average is five days, but it’s anywhere from 1 to 12 days that people start developing symptoms, usually starting with nausea, vomiting, and fever.
But then as the organism starts invading deeper into the brain, you start getting seizures, confusion, hallucinations, and eventually coma and death. Because what happens as the amoeba starts invading, they first start destroying the layer around the brain, the meninges, then they invade it. Then into the actual parenchyma of the brain, the part that allows you to think and do things.
That’s when you start getting symptoms like coma and confusion that creates a lot of swelling. All of that damage occurs to your brain. The swelling will eventually push your brain down through the little hole in your skull and the brainstem gets trapped.
The brainstem is where all the essential functions like telling your lungs to breathe occurs. So once that is pinched off and malfunctioning, then most people die of respiratory failure.
Kristen Meinzer:
What kind of testing is done? Let’s say I go to the hospital and I say something’s not right here. Is there some sort of test like a COVID rapid test or something that I can take where we know this is a case of an amoeba in my brain?
Dr. Pritt:
There is a fairly rapid test that we can do and that is often done when someone presents with signs that may indicate meningitis. That’s when you have an inflammation of the lining around the brain and in that case, it’s very common to obtain a little bit of cerebral spinal fluid through a procedure called a lumbar puncture, that’s when they stick a needle in your back and they draw out a little bit of that fluid that coats, and it goes around your brain, and they can examine that fluid for organisms.
The problem is, until you start experiencing symptoms, there’s probably no reason why you would go to a doctor. It’s only once you start experiencing symptoms, the nausea, vomiting, often an intense headache so bad, you could hardly sleep. Then you start getting later stage symptoms like what we call photophobia, where the light hurts your eyes and you have to shade yourself from the light. You also experience neck stiffness. Those are all pretty serious signs that would trigger someone, or if it was a child, a family member to bring that individual to the emergency room.
Because the symptoms are suggestive of meningitis, a lumbar puncture at that point would usually be one of the tests that’s performed. That’s your window of opportunity to make that diagnosis while it’s still possible to treat the patient. If you wait too long, try to tough it out, then you can slip into the later stage with coma and death, and it’s too late at that point. We have other ways of diagnosing infection, like biopsy of brain tissue and PCR, but by that point it really has gone too late.
Kristen Meinzer:
Because it’s so fast moving.
Dr. Pritt:
Yes. But we have had some cases that have been diagnosed early and it’s been exactly through that method of microscopic examination of cerebrospinal fluid.
Kristen Meinzer:
I don’t know about you, but I don’t really think I’m going to forget the stuff Dr. Pritt just said anytime soon. Let’s just say if you’ve been swimming around on a hot day, doing cannonballs, kicking up dust clouds from the bottom of the lake, and the next couple days you get a headache you can’t seem to shake, or start feeling nauseous, don’t tough it out. See a doctor. Let them check that brain fluid for you. Because that clock might be ticking. Okay, in those lucky cases, it’s discovered and it is what it is. This is Naegleria. What treatment is then administered?
Dr. Pritt:
No one knows the perfect treatment, but we’ve had four survivors, two of which have had no permanent neurologic damage. There’s hope. In those individuals, what really seemed to work was, first of all, inducing, hypothermia, deliberately lowering the body temperature, and then using a multi drug combination with Miltofacin, a broad spectrum antimicrobial, originally developed as a cancer treatment, but didn’t work great for that purpose, and Amphotericin B, an antifungal, Rifampin, an antibiotic, Fluconazole, another antifungal, steroids to decrease inflammation, and Azithromycin, another antibiotic.
Just a little extra context, Miltefosine is a broad spectrum antimicrobial. Amphotericin B is an antifungal. Rifampin is an antibiotic. Fluconazole is another antifungal, and Azithromycin is another antibiotic.
Kristen Meinzer:
That’s so fascinating. I was brought up thinking antibiotics are for this and anti this, they’re for that, but you’re saying that’s not always the case, that sometimes something that is maybe originally designed for this purpose can work for other things too.
Dr. Pritt:
Yes, absolutely. It may not be that all those drugs are necessary, but that was the drug combination or drug cocktail that was used in the people that did well. Probably the hypothermia, which cools down the body and slows everything down. It’s quite helpful.
Kristen Meinzer:
Because a cold amoeba is an unhappy amoeba.
Dr. Pritt:
Plus the steroids to decrease the inflammation.
Kristen Meinzer:
Your brain doesn’t try to squeeze out the bottom of your skull. It sounds like the best course of action is actually preventative in this case.
Dr. Pritt:
Yes. An ounce of prevention is worth a pound of cure, as they say. First of all we talked a lot about the water exposure. I should point out that the people that are jumping into water and having water forced up their noses are usually children, and that’s what we’re really seeing. Children are the risk group that we’re seeing for freshwater exposure, in fact, the CDC actually recommends using nose clips if you’re diving or jumping. Or just don’t jump and dive at all, especially during the summer months.
That’s the other thing to mention is this is an organism, as we said, that loves warm water. It’s thermophilic. The hot summer months, really the mid part of the summer, that’s when you’re going to have the greatest risk, especially if it’s been rather dry and lake levels are low, and you’re more likely to come in contact with the bottom and stir up the sediment. Those are potential times where you may be at greater risk.
Avoid vigorous swimming during that point, anything that would get water up your nose. Wear nose clips or keep your head above water. Definitely don’t want to put your head underwater in hot springs or other geothermal waters, spas, etcetera.
The CDC general guidelines are to avoid all sediment water when swimming. Now, it’s not just swimming, though. As we mentioned, there’s risks from tap water. There’s risks from man made bodies of water, like recreational water parks.
Kristen Meinzer:
I see.
Dr. Pritt:
It’s the same thing. You want to prevent anything that’s going to get water up your nose. If you’re using water for nasal irrigation, either for religious purposes or just to clear out your sinuses, you want to use distilled water or boil the water first.
Kristen Meinzer:
Along with avoiding diving into fresh water or so, without a nose clip, would it make a difference to maybe rinse out my nasal cavity after I’m in a freshwater source or at a water park? Does that make a difference?
Dr. Pritt:
There really haven’t been any studies that have shown that that would be a benefit. I guess I would worry that if there were organisms in the outside of your nose that you might end up flushing them deeper into your nasal cavities. I think again, prevention is key. Try to avoid getting the water up into your nose to begin with.
Kristen Meinzer:
Now, you said that when people have this amoeba it’s not always clear that they have it. Are there other diseases that are commonly mistaken for this amoeba? Are there misdiagnoses that are quite common?
Dr. Pritt:
Yes, first of all, it’s a fairly rare disease, but you are correct that when it does happen, it’s often mistaken or not recognized early on as being potentially an amoebic form of brain disease or brain infection. Instead, more likely, people probably think of things like viruses and bacteria, bacterial meningitis. Viral meningitis is relatively much more common.
There have been cases where people were put on antibiotics thinking it was a bacterial infection and not realizing it was an amoeba. Really, to get that early diagnosis, someone needs to look at the cerebrospinal fluid under the microscope and identify those amoebae in the CSF, and then that prompts the additional treatment.
Kristen Meinzer:
How worried should we be when we’re going into water parks, freshwater, or when we’re using our neti pot? Is something that should be on top of our minds at all times?
Dr. Pritt:
I’d say yes, but in a sense of being cautious, not panicked. Just like there are some things we do automatically; for example, if you wear contact lenses, hopefully you aren’t spitting on them or running them under the tap water. You’re only using sterile saline. It’s just something that you think of routinely.
I would say that we need to start thinking about routine measures to prevent amoebic infection of the brain, such as not getting your head underwater, especially if you’re at a hot spring. When you’re using a neti pot, just make sure you always have distilled water. Just make it part of your normal routine.
Kristen Meinzer:
These are things in our control, but then obviously there are things that are much bigger than us, like climate change. You can do all you can on a personal level, but it’s really hard on a global level to combat. I imagine because of that amoeba climate change is just making it a more hospitable world for amoeba, right?
Dr. Pritt:
It does appear to be, yes. The higher temperatures are going to make it more hospitable for the organism to survive in water, and you’re probably going to see more cases in the northern part of our countries.
For example, we’ve now had two cases in Minnesota. When we had the first case in Minnesota, that was the furthest north we had ever had a case. We’re probably going to see cases up into Canada as the temperatures in the water reach that higher temperature where the Nagloria really likes it. Temperatures that are going to change human behavior. You want to go for a swim when it’s really hot to cool down, and then you potentially expose yourself to water that has a lot of proliferating amoeba in it.
Then there’s other things with climate change that come as well. It’s not always just heat. We’re also seeing increased precipitation that could bring more soil into the lakes and ponds, which might give more silt for the organisms to live in. If there’s drought, on the other hand, then people may be collecting rainwater that comes down off their roofs. We’ve known that nuclear waste has been found in rainwater and collected into barrels.
It’s not necessarily coming down in the rain, but it’s proliferating in the barrel where it’s stored. Then lastly, the extreme events that we’ve been seeing on the news, like cyclones and floods, anything that involves water that could increase human exposure to water that could have Naegleria in it.
Kristen Meinzer:
It’s terrifying and amazing to think about how climate change changes everything from day to day life, our medical health to how we regulate our body temperatures. Like you said, a lake seems like a perfectly great thing to do, but what happens if all the hot days are not just here and there, but a regular thing?
Dr. Pritt:
Absolutely. I think we’ll see other changes with infectious diseases over time with climate change, perhaps the spreading of mosquitoes and ticks and increased exposure to other waterborne pathogens. People just have to be informed and know what the risks are and know what preventative measures to take.
Kristen Meinzer:
Excellent. This is me going hardcore. Why not just destroy all Naegleria? Can’t we just eliminate them from the planet? Is there any point in them existing?
Dr. Pritt:
We can’t and I don’t think we’d probably want to either. First of all, just the practicality of it. I don’t think it would be possible to go into every body of freshwater across the world and try to find them all and eliminate them. Probably anything we’d do to eliminate them would kill a lot of other good things.
Although I like where you’re going with that, because it definitely makes you wonder why we need these things in our life, but going into that, what good do they do? They are part of the natural food chain and they play an important role eating bacteria and algae and fungi. They are part of the whole web of life and we don’t really know what would happen if you eliminate it, part of that web, how that would impact everything else in the environment.
Kristen Meinzer:
I think that about a lot in life, honestly. I live in New York and I’m like, why?
Dr. Pritt:
Oh, I know, I know.
Kristen Meinzer:
I just want to thank you so much because everything you shared with us today was so illuminating, but it was so measured that I’m not going to leave listeners feeling like, “Oh, no, I can never touch water again.”
Dr. Pritt:
That was my goal.
Kristen Meinzer:
I really appreciate what you brought to the conversation. So thank you so much for joining us today.
Dr. Pritt:
Yeah, my pleasure. Thanks for the opportunity to join you. This was fun.
Kristen Meinzer:
I don’t think we need to rehash the gory details, but suffice it to say, yeah, a brain eating amoeba infection is pretty much guaranteed to be an unpleasant experience. That said, just to put things in perspective, in 2021, there were almost 3.5 million deaths in the US. That same year, there were 3 cases of Naegleria fowleri. We’re talking about a less than one in a million chance. If you want to reduce that risk even further, consider nose clips, or just don’t put your head in at all while swimming in freshwater.
Okay, that’s all for this episode. But if you’ve got a question or topic suggestion, please send us an email at mcppodcasts@mayo.edu, or leave us a voicemail at 507-538-6272 and we’ll see if we can help you out.
Please remember, this podcast cannot provide individual medical advice and the discussion presented here cannot replace a one-on-one consultation with a medical professional.
Thanks for listening. And until next time, take care and stay healthy.
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