Don’t Go In The Water? Naegleria Fowleri, the Brain-Eating Amoeba, and Your Chances of Getting It.

English: (Naegleria fowleri lifecycle stages. ...
English: (Naegleria fowleri lifecycle stages. A: Cyst of N. fowleri in culture. Naegleria fowleri does not form cysts in human tissue. Cysts in the environment and culture are spherical, 7-15 µm in diameter and have a smooth, single-layered wall. Cyst) (Photo credit: Wikipedia)

Today’s Kennebec Journal had a report of a young Arkansas girl, Kali Hardig, who has recovered from a brain-eating amoeba attack.  As with most reports of life-threatening strange illnesses, my family asked me what their chances of getting the illness were.  Unlike most dads, I have to find out the answer.  So here’s my best guess.

Short answer: pretty low.

Longer answer: slightly increasing. (See below).

For those of us in Maine, we can rest easier that Naegleria cysts up and becomes inactive at around 50 degrees. But in the summer we already have a case of a child from Minnesota who got the illness.  As the waters warm, the warm water critters come alive. (

Naegleria Fowleri is an interesting critter (it’s a protist, but that doesn’t translate to anyone outside a microbiology lab).  It can form a cyst, but will also act as an amoeba or grow flagella to move itself around.  When it attacks, it goes right up the olfactory (smelling) nerve of the nose and into the brain.  Pretty much like a bad Star Trek episode.

If you believe Wikipedia, almost no water source is safe.  There have been cases of people using water up their noses (neti pots) and tap water in Louisiana.  Cases from ablutions (dumping fresh water on your head) in various countries, and several cases where fresh water exposure hasn’t been documented.

In a turnabout of the rest of the world affecting North America, there is a good study on the possibility that the nasty species first mutated into itself here in North America.  (  Now it’s gone worldwide.

While Naegleria won’t grow in salt water, it likes warm water and geothermal springs. The amount of Naegleria in the world’s warm waters is very high.  One study of Naegeria in Texas reservoirs in 2013 found: “N. fowleri was detected in water samples from 67% of the reservoir sites tested.” (J Water Health. 2013 Jun;11(2):346-57. doi: 10.2166/wh.2013.162.)

In Guadeloupe, a study of geothermal waters showed: “Thermophilic amoebae were present at nearly all collection sites.” (PLoS One. 2013;8(1):e54414. doi: 10.1371/journal.pone.0054414. Epub 2013 Jan 18.)

In Taiwan, “Among the 60 samples obtained, Naegleria spp. was identified in 26 (43·3%) samples” in geothermal springs. (Lett Appl Microbiol. 2013 Jan;56(1):1-7. doi: 10.1111/lam.12006. Epub 2012 Nov 2.)

So is the answer to never let warm water go up your nose, and if it does happen you should rush to the hospital and get the drug miltefosine or the Wiki recommended Thorazine, (  knowing you have a very high likelihood of dying anyway?  That’s the impression the news reports gave of the illness.

Given the ubiquitous nature of Naegleria, it seems odd that more people aren’t dying of the amoeba.  In a ten-year period, thirty people got infected in the U.S. even though most of Texas has the critter in their reservoirs.  In the same time Guadeloupe, which has the critter everywhere, had one case.  No one would believe that only one child in Guadeloupe got water up his nose in the last ten years.

In the case of Thailand, there were twelve reported cases, with males being twice as likely to get the illness as females. At the time of the Thai report in 2004, fewer than two hundred cases had been reported worldwide. (MedGenMed. 2004 Mar 8;6(1):2.)

In India in 2008, only eight cases of the illness had been reported, with a male to female ratio of seven to one.  (J Assoc Physicians India. 2008 Jun;56:459-62.) Total cases in the U.S. from 1965 to 2010 were 118 cases, one quarter of those in Florida. (J Environ Health. 2013 Apr;75(8):26-31.)

Based on the case reports, either Thai and Indian warm water safety measures are superior to Florida, or there is another reason besides warm water contamination that someone gets Naegleria.

I tracked down the neti pot (pour water up your nose) tap water study, and it says that tap water can have Naegleria in it. (

I can remember the last warm shower I had.  Water might have gotten near or up my nose, and I’m still around to talk about it. In other words, Naegleria is in warm water, but for the most part it doesn’t get into us.

The growth of Naegleria can either become highly pathogenic (disease causing) or less pathogenic depending on the way it is grown. (Microbiology. 2012 Oct;158(Pt 10):2652-60. Epub 2012 Aug 9.) So even though the species is present in a body of water doesn’t necessarily mean it is highly pathogenic.

A study in Mexico of people who live with endemic (in all the water) Naegleria shows that the immune system of their noses responded to infection by Naegleria. The authors speculated that previous intestinal exposure to Naegleria could immunize locals against it. (Parasitol Res. 2000 Sep;86(9):775-80.)

Animal studies found that wild animals exposed to water had developed an immune response to Naegleria.(

In a mouse model, immunity to Naegleria was transferred from mother to child. (Kisaengchunghak Chapchi. 1989 Jun;27(2):79-86.)

Do I have a definitive answer? No. But I’ve got an idea of what I think we’re dealing with here.

First, we’re seeing slightly more cases of Naegleria because it’s being recognized and the waters are getting warmer.

Second, most people who are exposed to Naegleria do not get their brains eaten.  In fact, almost 99% of those exposed (number from the air) do not get the illness because otherwise every kid in our lakes and everywhere farther south would be keeling over in the summer.  Texas would be just gone from drinking the tap water from their reservoirs.

The only people who get this infection are those who did not get enough intestinal exposure (didn’t swallow enough lake water before snorting it up their noses).  They also had mothers who didn’t drink enough lake water and didn’t pass on any immunity.

The number of boys getting the illness is higher than girls, which makes me think that some level of inflammation (a bit of a bloody nose) may be involved in getting things started.

So we shouldn’t all go running off to the E.R. if our child inhales some lake water.  But we all should head to the E.R. if our child shows signs of: “epilepsy, weakness, cognitive decline, impaired consciousness, confusion, coma or focal neurological deficits (body parts failing).” Because Naegleria is not the only parasite that can cause problems.  I won’t list them all, but I counted twenty other classes of parasites.  (

Oh, and if a loved one does come down with Naegleria, there is a new study that outperforms Thorazine or miltefosine.  It’s mouse-based, but trying the drug might save a life. (Abstract below)

Antimicrob Agents Chemother. 2012 Nov;56(11):5450-7. doi: 10.1128/AAC.00643-12. Epub 2012 Aug 6.

Corifungin, a new drug lead against Naegleria, identified from a high-throughput screen.

Debnath A, Tunac JB, Galindo-Gómez S, Silva-Olivares A, Shibayama M, McKerrow JH.


Sandler Center for Drug Discovery, University of California, San Francisco, California, USA.


Primary amebic meningoencephalitis (PAM) is a rapidly fatal infection caused by the free-living ameba Naegleria fowleri. The drug of choice in treating PAM is the antifungal antibiotic amphotericin B, but its use is associated with severe adverse effects. Moreover, few patients treated with amphotericin B have survived PAM. Therefore, fast-acting and efficient drugs are urgently needed for the treatment of PAM. To facilitate drug screening for this pathogen, an automated, high-throughput screening methodology was developed and validated for the closely related species Naegleria gruberi. Five kinase inhibitors and an NF-kappaB inhibitor were hits identified in primary screens of three compound libraries. Most importantly for a preclinical drug discovery pipeline, we identified corifungin, a water-soluble polyene macrolide with a higher activity against Naegleria than that of amphotericin B. Transmission electron microscopy of N. fowleri trophozoites incubated with different concentrations of corifungin showed disruption of cytoplasmic and plasma membranes and alterations in mitochondria, followed by complete lysis of amebae. In vivo efficacy of corifungin in a mouse model of PAM was confirmed by an absence of detectable amebae in the brain and 100% survival of mice for 17 days postinfection for a single daily intraperitoneal dose of 9 mg/kg of body weight given for 10 days. The same dose of amphotericin B did not reduce ameba growth, and mouse survival was compromised. Based on these results, the U.S. FDA has approved orphan drug status for corifungin for the treatment of PAM.

PMID: 22869574

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