Naegleria (nay-GLEER-e-uh) infection is a rare and almost always fatal brain infection. Naegleria infection is caused by an amoeba commonly found in warm, freshwater lakes, rivers and hot springs. Exposure to the amoeba usually occurs during swimming or other water sports.

The amoeba — called Naegleria fowleri — travels up the nose to the brain, where it causes severe brain damage. Most people who have naegleria infection die within a week of showing symptoms.

Millions of people are exposed to the amoeba that causes naegleria infection each year, but only a handful of them ever get sick from it. Health officials don't know why some people develop naegleria infection while others don't.


Naegleria infection causes a disease called primary amebic meningoencephalitis (muh-ning-go-un-sef-uh-LIE-tis) — also known as PAM. PAM is a brain infection that leads to brain swelling and the destruction of brain tissue.

The symptoms of naegleria infection generally begin within two to 15 days of exposure to the amoeba. Initial signs and symptoms often include:

  • Fever
  • Sudden, severe headache
  • Nausea and vomiting
  • Nasal congestion or discharge
  • Changes in smell or taste

As the disease worsens, signs and symptoms may also include:

  • Stiff neck
  • Sensitivity to light
  • Confusion
  • Loss of balance
  • Sleepiness
  • Seizures
  • Hallucinations

The disease can progress rapidly and typically leads to death within about five days of the start of symptoms.

When to see a doctor

Seek immediate medical attention if you develop a sudden onset of fever, headache, stiff neck and vomiting, particularly if you have recently been in warm, fresh water.


Naegleria infection is caused by the Naegleria fowleri amoeba, which is most often found in bodies of warm, fresh water around the world, especially during the summer months. The amoeba is also sometimes found in soil. The amoeba enters your body through your nose via contaminated water, mud or dust, and travels to your brain through the nerves that transmit your sense of smell.

Only a tiny percentage of the millions of people who are exposed to Naegleria fowleri ever get sick from it. Why some people become infected after exposure and others don't isn't known.

The amoeba doesn't spread from person to person. You also can't be infected by drinking contaminated water. Salt water, such as ocean and sea water, and properly cleaned and disinfected swimming pools don't contain the naegleria amoeba.

Risk factors

Millions of people are exposed to the amoeba that causes naegleria infection each year, but only a few people get sick from it. Between 2010 and 2019, 34 infections were reported in the United States.

Some factors that might increase your risk of naegleria infection include:

  • Freshwater swimming. Most people who become ill have been swimming in a freshwater lake within the previous two weeks.
  • Heat waves. The amoeba thrives in warm or hot water. Infections are more likely to occur in the summer months and in southern states, but can also occur in more northern states.
  • Age. Children and young adults are the most likely age groups to be affected, possibly because they are likely to stay in the water longer and are more active in the water.
  • Nasal cleansing or irrigation. Very rarely, infections have occurred in people who used contaminated tap water to irrigate their sinuses or to cleanse their nose during religious practices. To ensure that your water is safe for sinus rinsing or ritual cleansing, don't use water straight from the faucet. Use boiled or distilled water instead.


The Centers for Disease Control and Prevention (CDC) suggests that the following measures may reduce your risk of naegleria infection:

  • Don't swim in or jump into warm freshwater lakes and rivers.
  • Hold your nose shut or use nose clips when jumping or diving into warm bodies of fresh water.
  • Avoid disturbing the sediment while swimming in shallow, warm fresh waters.

Nov. 07, 2020
  1. Parasites — Naegleria fowleri — Primary amebic meningoencephalitis (PAM) — Amebic encephalitis. Centers for Disease Control and Prevention. https://www.cdc.gov/parasites/naegleria/. Accessed Oct. 14, 2020.
  2. Seas C, et al. Free-living amebas and prototheca. https://www.uptodate.com/contents/search. Accessed Oct. 14, 2020.
  3. Kliegman RM, et al. Primary amebic meningoencephalitis. In: Nelson Textbook of Pediatrics. 21st ed. Elsevier; 2020. https://www.clinicalkey.com. Accessed Oct. 14, 2020.
  4. Bellini NK, et al. The therapeutic strategies against Naegleria fowleri. Experimental Parasitology. 2018; doi:10.1016/j.exppara.2018.02.010.


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