Zombies on Horseback: FAQ About Naegleria fowleri


This summer, two children and one young man died from one of the rarest infections commonly encountered in freshwater swimming holes - Naegleria fowleri, also known as the brain-eating amoeba or zombie amoeba. On average, N. fowleri claims the lives of 3-4 people a year in the U.S. during the dog days of summer when waters are relatively still and overly warm.

What is an amoeba?

An amoeba is a single-celled eukaryotic organism. The term “eukaryotic” is simply a classification label that tells you an organism’s DNA is surrounded by a membrane within a cell as opposed to floating freely within a cell as found in prokaryotes. For example we and the amoeba are both eukaryotes, while bacteria are prokaryotes. The majority of amoebae are non-harmful to man, however, one in particular - N. fowleri - causes death.

Where does Naegleria fowleri live?
N. fowleri is ubiquitous in nature. It can be found in streams, rivers, lakes, ponds, and yes…even drinking water from the tap if it is directly connected to an unfiltered water source such as a well in the countryside. Other sources that people usually consider safe may be a haven for the amoeba. Examples of this are natural hot springs, pools with too little chlorination, and surprisingly—water heaters in a home that are turned down to a temp below 116 degrees Fahrenheit to save on energy.

What does Naegleria fowleri eat?
Their primary food source is bacteria. However, when exposed to mammalian nerve cells N. fowleri earns its brain-eating moniker due to a pseudopodal-like, ring-shaped sucker structure that reaches out and attaches itself to a nerve cell.

How does Naegleria fowleri get to the brain?
N. fowleri typically enters through the nose during swimming and diving in lakes and ponds where water is often forced into the nasal passageways. The amoeba travels through the olfactory mucosa and along the cribriform plate toward the olfactory bulb nerves. From the olfactory nerves it makes its way through the floor of the cranium to the brain. At the brain it becomes pathogenic as it attacks the central nervous system causing the almost-always lethal condition primary amoebic meningoencephalitis (PAM).

How common are infections from Naegleria fowleri?
From 2001 to 2010 there were 32 reported deaths in the U.S. from N. fowleri infection. Thirty of those deaths resulted from swimming in recreational waters and two resulted from natural geothermal water drinking supplies. A recent case, however, was traced to an individual using tap water from his home to cleanse his nasal passages. Worldwide, there are approximately 400 reported cases of death due to N. fowleri.


How do I know if I might be infected?
Unfortunately the signs and symptoms of infection by N. fowleri are the same for a large number of other conditions. That, and the old maxim, “When you heat hoof beats—think horses not zebras,” taught to medical students is one of the reasons why infection by N. fowleri is often determined post mortem.

However, here is what you should look for: initial symptoms of fever, nausea, headache and stiff neck all begin within 1 to 7 days following exposure to the amoeba. Afterward, symptoms of confusion, loss of balance, hallucinations and seizures manifest as the amoeba eats away at the nervous system, which then rapidly progresses to death within a few to several days

If I am infected can I pass it onto my children?
No. N. fowleri is not like a virus—it cannot be passed from one individual to another.

Are there any effective treatments for infection from Naegleria fowleri?
There are medications from studies that have shown some efficacy; however, at this time the odds of surviving an infection from N. fowleri are slim. Only a handful of individuals diagnosed with the infection have survived. In the U.S. one 9-year-old girl survived after a month of hospitalization and treatment with antibiotics. Worldwide, 7 have survived infection.

What can I do to protect myself and my family?
The first thing to remember is that infection from N. fowleri is an extremely rare condition and only appears to be prevalent because of media coverage every summer when one individual (and usually, tragically a child), out of millions swimming during the summer die from the infection. To put it in some perspective, between 1996 and 2005 there were 36,000 drowning deaths in the U.S.

The only certain way to avoid N. fowleri is to refrain from swimming in recreational waters or municipal pools that do not properly chemically treat their water. Suggested precautions listed by the Centers for Disease Control and Prevention (CDC) include wearing nose clips to prevent water from entering through the nose; avoid freshwater activities during times of low water levels and high temperatures; and, do not stir up the sediment near the water’s edge in warm freshwater areas.

One final thought:
Being your own patient advocate is as important with a minor cold as it is with a serious disease. If you have been swimming in warm water this summer and within days feel the beginning of the signs and symptoms of N. fowleri infection, see your physician. And while he is examining you, just remind him that while he is listening for hoof beats and thinking of horses…to think of a horse with possibly a zombie riding on its back.

Source: Centers for Disease Control and Prevention