The Most Horrible Parasite: Brain Eating Amoeba

Naegleria fowleri is an amoeba that has not only developed a deadly taste for human brains but is also a match for our defences and stars in dramatic headlines. What happens when this monster enters your body?

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.

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). 

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. Soil

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. 

Naegleria fowleri eats other organisms like bacteria found in the sediment in lakes and rivers.

Naegleria fowleri infections are rare*. In the ten years from 2011 to 2020, 33 infections were reported in the U.S. Of those cases, 29 people were infected by recreational water, three people were infected after performing nasal irrigation using contaminated tap water, and one person was infected by contaminated tap water used on a backyard slip-n-slide.

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

Naegleria fowleri infection cannot be spread from one person to another.

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).

The infection destroys brain tissue causing brain swelling and death.

The fatality rate is over 97%. Only four people out of 151 known infected individuals in the United States from 1962 to 2020 have survived.

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.