Brain-Eating Amoeba

Naegleri fowleri is an amoeba that can cause a serious central nervous system infection. The amoeba is found in warm and still fresh water bodies of water and enters a human body through the nose. Successful treatment has included miltefosine.


What is brain-eating amoeba (Naegleria fowleri)?

Naegleria fowleri is an amoeba that lives throughout the world in warm and shallow bodies of fresh water, such as lakes, rivers and hot springs. It also lives in soil. It’s considered a free-living organism because it doesn’t need a host to live.

People who become infected by this amoeba develop a condition called primary amoebic meningoencephalitis (PAM). PAM is a very serious infection of the central nervous system that’s almost always fatal.

Note: You might also see the words “ameba” instead of “amoeba” and “amebic” instead of “amoebic.” Amoeba is more common than ameba, but both words refer to an organism with one cell.


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How do you get infected by brain-eating amoeba (Naegleria fowleri)?

The most common way of being infected by this type of amoeba happens when infected water goes into your nose. From there, the amoeba goes to your brain. This usually happens when you’re swimming, diving or doing something like water skiing in infected water. In extremely rare cases, the infected water can be heated tap water or swimming pool water that isn’t chlorinated enough.

You can’t be infected by swallowing infected water.

How common is an infection due to brain-eating amoeba (Naegleria fowleri)?

Luckily, there are only a few cases each year in the U.S. (estimated to be between zero and eight). Most of the cases happen in the southern states, such as Florida and Texas, and involve young males.

In later years, though, some cases have happened in northern states during periods of very hot weather. This change in where infections happen could be due to climate change.

Studies are being done that call into question how rare infection with Naegleria fowleri really is. Some people have antibodies to the amoeba, indicating that they’ve been infected and survived. Some cases of deaths attributed to meningitis have been reclassified as deaths due to brain-eating amoeba (Naegleria fowleri).

Another question is, why some people aren’t infected with the amoeba even though they’re in the same place doing the same things as people who’ve been infected?


Symptoms and Causes

What are the symptoms of infection with brain-eating amoeba (Naegleria fowleri)?

The signs and symptoms of primary amoebic meningoencephalitis (PAM) come on suddenly and are severe at the start, including:

  • High fever.
  • Very painful headache.
  • Nausea and vomiting.
  • Trembling.
  • Symptoms like those of meningitis, including a stiff neck and extreme sensitivity to light (photophobia).
  • Mental confusion.
  • Coma.

The fatality rate is higher than 97% even with treatment.

What causes infection with brain-eating amoeba (Naegleria fowleri)?

The infection occurs when the amoeba known as Naegleria fowleri gets into your brain through your nasal cavity. It can enter your body if you inhale any infected water. Usually, the amoeba lives in freshwater bodies of water that are warm, including hot springs (geothermal water).

You can also be infected by inhaling infected dust.

There have been other cases of reported infection by brain-eating amoeba (Naegleria fowleri) due to people using tap water rather than distilled or sterilized water to rinse out their noses with devices like a neti pot.


How long is the incubation period for infection with brain-eating amoeba (Naegleria fowleri)?

It takes about two to 15 days after you’ve been exposed to the amoeba for symptoms to develop.

Can I get infected with brain-eating amoeba (Naegleria fowleri) from being around someone who has it?

No. There haven’t been any cases found where the infection spread from person to person. There are studies underway to see if the infection can spread by tissue or organ donation.

Diagnosis and Tests

How is infection with brain-eating amoeba diagnosed?

If a healthcare provider thinks you might’ve been infected by brain-eating amoeba (Naegleria fowleri), they’ll recommend a spinal tap — also known as lumbar puncture — to see if the organism is in your cerebrospinal fluid (CSF).

Your provider may also recommend a brain biopsy. During this procedure, they’ll take a tissue sample and examine it under a microscope to check for the presence of the amoeba.

Management and Treatment

How is infection with brain-eating amoeba (Naegleria fowleri) treated?

The treatment of choice for primary amoebic meningoencephalitis (PAM), or infection with brain-eating amoeba (Naegleria fowleri) is the antifungal amphotericin B. Some survivors in North America were treated with a combination of drugs that included amphotericin B, rifampin, fluconazole and a drug called miltefosine. Miltefosine is a drug approved for treating leishmaniasis, a parasitic disease that’s spread by sandflies.

The best results (in two children who recovered completely) came from early diagnosis and treatment with the recommended drugs, along with cooling the body to below-normal temperature to treat brain swelling.


How can I prevent myself from being infected with brain-eating amoeba (Naegleria fowleri)?

Because the outlook for this condition is so dire, prevention can be important, even though the condition is very rare. These are key things to remember:

  • Don’t swim, wade or do watersports in warm freshwater locations, especially still waters, without nose plugs. Don’t go into the water at all if Naegleria fowleri is known to be present or likely to be present.
  • Don’t use tap water for a neti pot or any other device that cleans your nasal passages. Only use distilled or sterilized water. If you must use tap water, make sure that you boil it for one minute and then let it cool. If you live somewhere that’s 6,500 feet above sea level, boil the water for three minutes and let cool.
  • You can use filters to remove germs from water. Use filters labeled “NSF 53,” “NSF 58” or “absolute pore size of 1 micron or smaller.”
  • You can also use chlorine bleach liquid or tablets to disinfect your water for cleaning your nose and sinuses. Disinfecting water for nasal use requires a different amount of bleach than disinfecting water for drinking.
  • If you do develop symptoms of fever or headache after going into warm freshwater, tell your healthcare provider where you’ve been.

Outlook / Prognosis

What is the prognosis (outlook) for people who are infected with brain-eating amoeba (Naegleria fowleri)?

The outlook for someone who is infected with Naegleria fowleri is very poor. Even with treatment, most people die from this condition. Coma followed by death usually happens in a week or 10 days after symptoms and signs begin.

Living With

When should I see my healthcare provider if I have questions about infection with brain-eating amoeba (Naegleria fowleri)?

If you get feverish or have a headache after you’ve been active in a warm freshwater body of water or after you’ve used tap water to irrigate your nasal pages, see a healthcare provider or go to the emergency room immediately. Early diagnosis and treatment of infection with brain-eating amoeba (Naegleria fowleri) is critical.

A note from Cleveland Clinic

Hearing about a condition caused by a brain-eating amoeba and knowing how dangerous it can be is certainly scary. If you think you may have been exposed to the amoeba, get immediate medical help. But it’s important to remember how very rare this condition is. You can do your part in preventing it by using only distilled or sterilized water to rinse your nasal passages and by avoiding water you suspect may be infected, especially in hot weather.

Medically Reviewed

Last reviewed on 11/29/2022.

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