National Geographic Daily News
A freshwater amoeba.

The feeding structures of the amoeba Naegleria fowleri have a face-like appearance.

Image by D.T. John & T.B. Cole, Visuals Unlimited

Jaclyn Skurie

National Geographic

Published August 14, 2013

A second child is battling infection by a typically fatal parasite that enters through the nose and consumes brain tissue.

Weeks after a 12-year-old Arkansas girl contracted the parasite while swimming in a sandy-bottom lake at a water park in Little Rock, the Florida Department of Health has confirmed a case in Glades County, Florida. A 12-year-old boy was hospitalized over the weekend, his family told CNN affiliate WBBH, after kneeboarding in a water-filled ditch near his house.

This rare form of parasitic meningitis—primary amebic meningoencephalitis (PAM)—is caused by an amoeba called Naegleria fowleri. That microscopic amoeba—part of the class of life called protozoans—is a naturally occurring organism that normally feeds on bacteria and tends to live in the sedimentary layer of warm lakes and ponds.

According to the Centers for Disease Control and Prevention (CDC), victims die from the amoeba after about 5 days. Since 1962 there has only been one survivor, yet the 12-year-old girl who was hospitalized last month has improved enough to be moved out of the intensive care unit at Arkansas Children's Hospital, hospital spokesman Tom Bonner told CNN.

(See "Giant Amoebas Found in Deepest Place on Earth.")

To find out more about Naegleria fowleri, National Geographic got in touch with Jonathan Yoder, an epidemiologist at the CDC  who collects and analyzes data on the microscopic amoeba.

How does this amoeba called Naegleria fowleri infect a human?

Under certain conditions, Naegleria fowleri can develop flagella—threadlike structures that enable it to rapidly move around and look for more favorable conditions. When people swim in warm freshwater during the summer, water contaminated with the moving amoeba can be forced up the nose and into the brain.

This causes headache, stiff neck, and vomiting, which progresses to more serious symptoms. Between exposure and onset, infection generally results in a coma and death after around five days.

Where is it found?

We see it in warm freshwater or in places with minimal chlorination. It is not uncommon to detect the amoeba if you sample freshwater in warm weather states.

Can it live in swimming pools?

There have been no evident cases of contamination in the United States in well-maintained, properly treated swimming pools. Filtration and chlorination or other types of disinfectant should reduce or eliminate the risk.

But it does get a bit trickier—there was a case in Arizona about ten years ago where a kid swam in a pool filled with water from a geothermal hot water source before it was treated. Unfortunately, the kid became ill and died.

Are cases of infection becoming more common?

We don't have data that says infection from Naegleria fowleri is becoming more common. In the last few years there have been four to five cases per year.

What has changed recently is that cases have appeared in places we had never seen before—like Minnesota, Indiana, and Kansas. This is evidence that the amoeba is moving farther north. In the past it was always found in warmer weather states.

Why does the amoeba enter the nose of some people but not others?

That is a very good question we don't know the answer to. Millions of people swim in these bodies of water every year and don't become ill. So it is difficult for us to say why one person would become ill and other people who swam in the same place and did the same activities did not. It certainly can affect anyone.

What is the chance of survival?

Since 1962, there have been 128 cases of Naegleria fowleri [infection] and only one survivor, not including the current case. Back in 1978, a patient survived after being treated with antibiotics. The same regimen has been tried unsuccessfully on other patients.

How can people stay safe?

If people want to reduce their risk of becoming infected—even though this is a rare event—the thing to think about is holding their nose shut or wearing nose clips when swimming in warm, untreated freshwater. Keep your head above water in hot springs or other thermally heated bodies of water, and during activities where water is forced up the nose, like water sports and diving.

Another way to reduce the risk of infection is to avoid stirring up the sediment in lakes and ponds, where the amoeba may live.

This is a tragic event for someone who becomes infected, as well as their family. We feel it is important for us to be involved even though it does not affect lots of people each year.

This interview has been edited and condensed.

Follow Jaclyn Skurie on Twitter.

13 comments
MArk C
MArk C

Very tragic however looking at this in perspective only
about 5 (five) cases per year in the US for this.

compare to Number of deaths for leading causes of death in the US per year:

Heart disease: 597,689

Cancer: 574,743

Chronic lower respiratory diseases: 138,080

Stroke (cerebrovascular diseases): 129,476

Accidents (unintentional injuries): 120,859

Alzheimer's disease: 83,494

Diabetes: 69,071

Nephritis, nephrotic syndrome, and nephrosis: 50,476

Influenza and Pneumonia: 50,097

MArk C
MArk C

Very tragic however looking at this in perspective only
about 5 (five) cases per year in the US for this.

compare to Number of deaths for leading causes of death in the US per year:

Heart disease: 597,689

Cancer: 574,743

Chronic lower respiratory diseases: 138,080

Stroke (cerebrovascular diseases): 129,476

Accidents (unintentional injuries): 120,859

Alzheimer's disease: 83,494

Diabetes: 69,071

Nephritis, nephrotic syndrome, and nephrosis: 50,476

Influenza and Pneumonia: 50,097

Jerry Verdugo
Jerry Verdugo

It's a shame that this type of disease exists, because everyone knows that the "ol' swimming hole" is the best place to develop a healthy immune system for youngsters.  Fortunately, the article states that most people who swim in the same warm water do not acquire this amoebic disease.  This is very strange to me. Is it possible that most people have an immunity against this type of amoeba?

Jerry Verdugo
Jerry Verdugo

It's a shame that this type of disease exists, because everyone knows that the "ol' swimming hole" is the best place to develop a healthy immune system for youngsters.  Fortunately, the article states that most people who swim in the same warm water do not acquire this amoeba.  This is very strange to me. Is it possible that most people have an immunity against this type of amoeba?

Chaitanya Vadlamudi
Chaitanya Vadlamudi

I never swim in lakes, ponds and oceans only in pools. Really scary!!!!!!!!!

Charlie N.
Charlie N.

I won't try swimming in lakes anymore

Monica Matamoros
Monica Matamoros

Well.... I guess I won't be swimming in freshwater for a while

How to Feed Our Growing Planet

  • Feed the World

    Feed the World

    National Geographic explores how we can feed the growing population without overwhelming the planet in our food series.

See blogs, stories, photos, and news »

The Innovators Project

  • Brave Sage of Timbuktu

    Brave Sage of Timbuktu

    Abdel Kader Haidara had made it his life's work to document Mali's illustrious past. When the jihadists came, he led the rescue operation to save 350,000 manuscripts.

See more innovators »

Phenomena

  • How Sloths Save Their Energy

    How Sloths Save Their Energy

    They effectively "tape" their internal organs to their ribs and hips to prevent pressure on the lungs. By Ed Yong.

See more posts »

Latest News Video

See more videos »

See Us on Google Glass

Shop Our Space Collection

  • Be the First to Own <i>Cosmos: A Spacetime Odyssey</i>

    Be the First to Own Cosmos: A Spacetime Odyssey

    The updated companion book to Carl Sagan's Cosmos, featuring a new forward by Neil deGrasse Tyson is now available. Proceeds support our mission programs, which protect species, habitats, and cultures.

Shop Now »