Naegleria fowleri (N. fowleri) facts
*Naegleria fowleri facts written by Charles Patrick Davis, MD, PhD
- Naegleria fowleri (N. fowleri, brain-eating amoeba) is a member of Acanthamoeba and is a free-living amoeba that lives in warm freshwater (for example, hot springs, lakes, and rivers) and in the soil. Only one type, N. fowleri, infects humans and causes amoebic meningoencephalitis (also termed primary amoebic meningoencephalitis [PAM], and Naegleriasis). The trophozoite stage is infective. Another free-living amoeba, Balamuthia mandrillaris, can cause granulomatous amoebic encephalitis. People also refer to it as a brain-eating amoeba.
- Naegleria fowleri infects people when it reaches the nasal cavity, usually after contaminated water or soil forcefully enters the nasal cavity (for example, diving into the water and forcing water into the new cavity). It can migrate up the olfactory nerve, through the cribriform plate, and then cross the blood-brain barrier to cause the brain infection.
- Naegleria fowleri exists mainly in warm freshwater like lakes, rivers, hot springs, where warm water discharges from industrial plants, swimming pools and water parks that are poorly maintained and/or not chlorinated properly, water heaters, and even in the soil. The amoeba doesn't live in saltwater.
- Naegleria fowleri grows best at temperatures up to 115 F (46 C).
- Naegleria fowleri uses bacteria and similar organisms for food.
- Naegleria fowleri cannot survive in a cleaned, maintained, and disinfected swimming pool.
- Infectious diseases data indicates that infections are rare with this amoeba. From 2008-2017, there were 34 reported infections in the United States -- 30 in recreational water (lakes and rivers, for example), three after nasal irrigation, and one from using a Slip 'N Slide with contaminated water.
- Most infections occur during the summer in the southern states in the U.S.
- Naegleria fowleri infections are not contagious from person to person.
- Naegleria fowleri infection has an incubation period that ranges from one to nine days (average five days).
- The initial symptoms of Naegleria fowleri infection may include headache, fever, nausea, and/or vomiting. Later symptoms may include stiff neck, confusion, loss of balance, seizures, and hallucinations. After the start of symptoms, the disease usually causes death within one to 12 days (with an average five days).
- The mechanism of death from this amoeba is due to destroyed brain tissue and brain swelling.
- The fatality rate is over 97%. Since 1962, only four people out of 143 known infected have survived an infection with Naegleria fowleri.
- Effective treatment for infection is questionable. However, two people with Naegleria fowleri infection survived after be treated with miltefosine in combination with other drugs (for example, amphotericin B). The successful treatment gives researchers some hope for future treatments.
- If someone develops a sudden onset of fever, headache, nausea/vomiting, and stiff neck, they should immediately seek medical care, especially if they have participated in warm water activities recently.
- Although the amoeba thrives in the warm South, it has caused infections in a few northern states.
- There is no routine and rapid test for Naegleria fowleri in water. However, researchers are trying to develop such tests.
- Researchers suggest that recreational water users should assume that Naegleria fowleri is present warm freshwater across the United States.
- Risk reduction for this infection involves preventing or limiting water going up the nose; nose clips may help and avoiding head dunking in areas of warm untreated water may limit your risk.
What is Naegleria?
Naegleria is an ameba (single-celled living organism) commonly found in warm freshwater (for example, lakes, rivers, and hot springs) and soil. Only one species (type) of Naegleria infects people: Naegleria fowleri.
How does infection with Naegleria fowleri occur?
Naegleria fowleri infects people when water containing the ameba enters the body through the nose. This typically occurs when people go swimming or diving in warm freshwater places, like lakes and rivers. The Naegleria fowleri ameba then travels up the nose to the brain where it destroys the brain tissue.
You cannot be infected with Naegleria fowleri by drinking contaminated water. In very rare instances, Naegleria infections may also occur when contaminated water from other sources (such as inadequately chlorinated swimming pool water or contaminated tap water) enters the nose, for example when people submerge their heads or cleanse their noses during religious practices, and when people irrigate their sinuses (nose) using contaminated tap water. Naegleria fowleri has not been shown to spread via water vapor or aerosol droplets (such as shower mist or vapor from a humidifier).
Where is Naegleria fowleri found?
Naegleria fowleri is found around the world. In the United States, the majority of infections have been caused by Naegleria fowleri from freshwater located in southern-tier states. The ameba can be found in:
- Bodies of warm freshwater, such as lakes and rivers
- Geothermal (naturally hot) water, such as hot springs
- Warm water discharge from industrial plants
- Geothermal (naturally hot) drinking water sources
- Swimming pools that are poorly maintained, minimally-chlorinated, and/or un-chlorinated
- Water heaters. Naegleria fowleri grows best at higher temperatures up to 115°F (46°C) and can survive for short periods at higher temperatures.
Naegleria fowleri is not found in salt water, like the ocean.
In what water temperature does Naegleria fowleri cause infection?
Naegleria fowleri is a heat-loving (thermophilic) organism. It grows best at higher temperatures up to 115°F (46°C) and can survive for short periods at higher temperatures. It is less likely to be found in the water as temperatures decline. The ameba can be found in lake or river sediment at temperatures well below where one would find the ameba in the water.
What is the source of food for Naegleria fowleri?
Naegleria fowleri eats other organisms like bacteria found in the sediment in lakes and rivers.
Can I get a Naegleria fowleri infection from a disinfected swimming pool?
No. You cannot get a Naegleria fowleri infection from a properly cleaned, maintained, and disinfected swimming pool.
How common are Naegleria fowleri infections in the United States?
Naegleria fowleri infections are rare. In the 10 years from 2008 to 2017, 34 infections were reported in the U.S. Of those cases, 30 people were infected by recreational water, 3 people were infected after performing nasal irrigation using contaminated tap water, and 1 person was infected by contaminated tap water used on a backyard slip-n-slide.
When do Naegleria fowleri infections most commonly occur?
While infections with Naegleria fowleri are rare, they occur mainly during the summer months of July, August, and September. Infections are more likely to occur in southern-tier states, but can also occur in other more northern states. Infections usually occur when it is hot for prolonged periods of time, which results in higher water temperatures and lower water levels.
Bacterial Infections 101: Types, Symptoms, and Treatments
Can infection be spread from one person to another?
No. Naegleria fowleri infection cannot be spread from one person to another.
What are the symptoms of Naegleria fowleri infection?
Naegleria fowleri causes the disease primary amebic meningoencephalitis (PAM), a brain infection that leads to the destruction of brain tissue. In its early stages, symptoms of PAM may be similar to symptoms of bacterial meningitis.
Initial symptoms of PAM start about 5 days (range 1 to 9 days) after infection. The initial symptoms may include headache, fever, nausea, or vomiting. Later symptoms can include stiff neck, confusion, lack of attention to people and surroundings, loss of balance, seizures, and hallucinations. After the start of symptoms, the disease progresses rapidly and usually causes death within about 5 days (range 1 to 12 days).
What is the actual mechanism of death from Naegleria fowleri infection?
The infection destroys brain tissue causing brain swelling and death.
What is the fatality rate for an infected person who begins to show signs and
The fatality rate is over 97%. Only 4 people out of 143 known infected individuals in the United States from 1962 to 2017 have survived.
Is there effective treatment for infection with Naegleria fowleri?
It is not clear. Several drugs are effective against Naegleria fowleri in the laboratory. However, their effectiveness is unclear since almost all infections have been fatal, even when people were treated with similar drug combinations. Recently, two people with Naegleria infection survived after being treated with a new drug called miltefosine that was given along with other drugs and aggressive management of brain swelling.
What should I do if I have been swimming or playing in freshwater and now
think I have symptoms associated with Naegleria fowleri?
Infection with Naegleria fowleri is rare. The early symptoms of Naegleria fowleri infection are similar to those caused by other more common illnesses, such as bacterial meningitis. People should seek medical care immediately whenever they develop a sudden onset of fever, headache, stiff neck, and vomiting, particularly if they have been in warm freshwater recently.
How common is Naegleria fowleri in the environment?
Naegleria fowleri is commonly found in lakes in southern-tier states during the summer but more recently has caused infections in northern states. This means that recreational water users should be aware that there will always be a low level risk of infection when entering these waters. In very rare instances, Naegleria has been identified in water from other sources such as inadequately chlorinated swimming pool water or heated and contaminated tap water. Naegleria fowleri grows best at higher temperatures up to 115°F (46°C) and can survive for short periods at higher temperatures.
Is there a routine and rapid test for Naegleria fowleri in the water?
No. It can take weeks to identify the ameba, but new detection tests are under development. Previous water testing has shown that Naegleria fowleri is commonly found in freshwater venues. Therefore, recreational water users should assume that there is a low level of risk when entering all warm freshwater, particularly in southern-tier states.
How does the risk of Naegleria fowleri infection compare with other
The risk of Naegleria fowleri infection is very low. There have been 34 reported infections in the U.S. in the 10 years from 2008 to 2017, despite millions of recreational water exposures each year. By comparison, in the ten years from 2001 to 2010, there were more than 34,000 drowning deaths in the U.S.
What swimming behaviors have been associated with Naegleria fowleri
Behaviors associated with the infection include diving or jumping into the water, submerging the head under water or engaging in other water-related activities that cause water to go up the nose.
How will the public know if a lake or other water body has Naegleria fowleri?
Recreational water users should assume that Naegleria fowleri is present in warm freshwater across the United States. Posting signs based on finding Naegleria fowleri in the water is unlikely to be an effective way to prevent infections. This is because:
- Naegleria fowleri occurrence is common, infections are rare.
- The relationship between finding Naegleria fowleri in the water and the occurrence of infections is unclear.
- The location and number of amebae in the water can vary over time within the same lake or river.
- There are no rapid, standardized testing methods to detect and quantitate Naegleria fowleri in water.
- Posting signs might create a misconception that bodies of water without signs or non-posted areas within a posted water body are Naegleria fowleri-free.
How can I reduce the risk of infection with Naegleria fowleri?
Naegleria fowleri infects people when water containing the ameba enters the body through the nose. Infection is rare and typically occurs when people go swimming or diving in warm freshwater places, like lakes and rivers. Very rarely, infections have been reported when people submerge their heads or get water up their nose, cleanse their noses during religious practices, or irrigate their sinuses (nose) using contaminated tap or faucet water. Naegleria fowleri can grow in pipes, hot water heaters, and water systems, including treated public drinking water systems.
Personal actions to reduce the risk of Naegleria fowleri infection should focus on limiting the amount of water going up the nose and lowering the chances that Naegleria fowleri may be in the water.
Reviewed on 10/17/2018
United States. Centers for Disease Control and Prevention. "Parasites -- Naegleria fowleri -- Primary Amebic Meningoencephalitis (PAM) -- Amebic Encephalitis: Frequently Asked Questions." July 17, 2018. <https://www.cdc.gov/parasites/naegleria/general.html>.