The Brain-Eating Amoeba: Naegleria Fowleri

Amoebae are microbes that cause infectious diseases in people. Naegleria fowleri causes an infection of the central nervous system that must be diagnosed early.
The Brain-Eating Amoeba: Naegleria Fowleri

Last update: 20 August, 2021

Microorganisms are the main cause of numerous diseases in the world. Among the entire universe of pathogens that exist and that can affect humans, we have Naegleria fowleri.

The term infection is probably associated with bacteria and viruses, which are included among these pathogens. But did you know that there are amoebae that cause infections in the brain? In this article, we’ll discuss the curious case of an amoeba known as the brain-eating amoeba.

What are amoebae?

Amoebae are protozoa, free-living eukaryotic microorganisms that cause serious infections in humans. The illnesses they cause are characterized by a high mortality rate, which poses a challenge for their diagnosis and treatment.

Of all the genera that exist in nature, only four cause infections in humans and animals, among which we find the following species:

  • Balamuthia mandrillaris (genus Balamuthia)
  • Naegleria fowleri (genus Naegleria)
  • Sapinia pedata (genus Sapinia)
  • Various species of Acanthamoeba

These amoebae can be present in various environments, in water, soil, and air. But above all, amoebae nest in places where water is stagnant, such as sewage, swimming pools, aquariums, and even in contact lens fluid.

They are also protozoa that need to complete their life cycle inside an organism that acts as a host, which is why they’re considered parasites. Amoeba infections directly affect the central nervous system, being lethal in most cases.

Naegleria fowleri swimming in water.
The scientific name of the brain-eating amoeba is Naegleria fowleri.

Continue reading: Intestinal parasites – their common symptoms

Naegleria fowleri

This parasite, known as the brain-eating amoeba, causes primary amebic meningoencephalitis (PAM), a chronic infection that lasts a few days. In most cases, the infection leads to the death of the host. It affects mostly young adults and healthy children, i.e. immunocompetent patients.

People who become infected with this amoeba are those who have swum in, or been in contact with, contaminated freshwater such as:

  • Heated swimming pools
  • Ponds
  • Lakes
  • Sewage systems

Transmission occurs by inhalation of water infested with Naegleria fowleri. From that moment on, it enters through the nostrils until it reaches the olfactory bulb, which is in contact with the frontal lobe of the brain.

Symptoms of this disease appear between days 5 and 7 after infection and develop rapidly within 24 hours. When the microorganism reaches the olfactory bulbs, an inflammatory response is induced, and hemorrhagic areas in the cerebral cortex become evident.

The symptoms that appear in the earliest stages are those common to meningitis, with headaches, high fever greater than 38 ºC, stiff neck, nausea, vomiting, and abnormal behavior.

Subsequently, these symptoms are accentuated so that the patient may suffer convulsions or even go into a coma. In the end, nerve paralysis caused by cerebral edema sets in, and increased intracranial pressure leads to death.

Diagnosis for Naegleria fowleri

For early diagnosis, doctors perform a direct analysis of cerebrospinal fluid, neuroimaging methods, and magnetic resonance imaging. They also perform microscopic examinations, both of the cerebral hemispheres, brainstem, cerebellum, as well as the upper part of the spinal cord.

The development of real-time PCR assays allows specific identification of the presence of amoebae from microbiological cultures.

Early diagnosis is key to curbing the infection. In fact, less than 5% of people suffering from this pathology survive if detection doesn’t take place in the earliest stages. Therefore, it’s essential that the patient mention that they’ve been in contact with fresh water.

It’s often challenging to diagnose an amebic meningoencephalitis infection due to the following considerations:

  • Lack of the necessary tools to detect it
  • Lack of knowledge in the health care team
  • Antibiotic resistance
  • Risk factors in countries where symptoms similar to other infections, such as meningitis, are more likely to develop
A young woman with a stiff neck.
Nuchal rigidity is a symptom of meningitis that can occur during the course of brain-eating amebiasis.

Find out more: Stiff Neck? Try These Home Remedies!


Unfortunately, there are few cases of patients who have survived primary amoebic meningitis. However, that being said, the drug used to treat this disease is the antifungal compound called amphotericin.

This drug is very effective against Naegleria fowleri, as long as its use takes place in the earliest stages of infection. What’s more, in a study on a related case, doctors used different antibiotics and amphotericin B was the most effective, and the patient recovered successfully.

At the same time, studies have shown that phenothiazine compounds (chlorpromazine and trifluoperazine) are able to eliminate this protozoan. Similarly, the antibiotic azithromycin has positive effects. Finally, the use of miltefosine is also detrimental to free-living amoebae.

Early diagnosis is crucial in Naegleria fowleri

As we’ve seen, infections caused by amoebae are relatively infrequent, and this is probably due to the difficulties that hinder their diagnosis. However, cases are increasing over the years, posing a public health problem.

Therefore, there’s an urgent need for researchers to devote their attention to the study of these diseases in order to advance diagnosis and treatment. Timely suspicion could save lives and decrease the lethality of the brain-eating amoeba.

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