Naegleria fowleri

Naegleria fowleri is commonly referred to as the “brain-eating amoeba” or “brain-eating ameba”. It is a free-living microscopic ameba, (single-celled living organism). It can cause a rare and devastating infection of the brain called primary amebic meningoencephalitis (PAM).

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Naegleria fowleri

Habitat

The ameba is commonly found in warm freshwater (e.g. lakes, rivers, and hot springs) and soil.

• Naegleria fowleri usually infects people when contaminated water enters the body through the nose.
• Once the ameba enters the nose, it travels to the brain where it causes primary amebic meningoencephalitis (PAM), which is usually fatal.
• Infection typically occurs when people go swimming or diving in warm freshwater places, like lakes and rivers.
• In very rare instances,
• Naegleria infections may also occur when contaminated water from other sources (such as inadequately chlorinated swimming pool water or heated and contaminated tap water) enters the nose.
• You cannot get infected from swallowing water contaminated with Naegleria.

Pathogenesis

• PAM is caused by Naegleria fowleri, a free-living ameba. It is a rare but serious disease that is often fatal
• Humans become infected when water containing Naegleria fowleri enters the nose and the ameba migrates to the brain along the olfactory nerve.
• People do not become infected from drinking contaminated water.

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Naegleria fowleri infection

Symptoms

• Symptoms start 1-9 days (median 5 days) after swimming or other nasal exposure to Naegleria-containing water.
• People die 1-18 days (median 5 days) after symptoms begin.
• PAM is difficult to detect because the disease progresses rapidly so that diagnosis is usually made after death.

Stages

Signs and symptoms of the infection include:

Stage 1

• Severe frontal headache
• Fever
• Nausea
• Vomiting

Stage 2

• Stiff neck
• Seizures
• Altered mental status
• Hallucinations
• Coma

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Naegleria fowleri lifecycle stages

Mortality

• The disease is generally fatal.
• Overall, the outlook for people who get this disease is poor, although early diagnosis and new treatments might increase the chances for survival.
• With early diagnosis, and treatment with Mifepristone can reduce the mortality.

Detection

• Primary amebic meningoencephalitis (PAM) is a serious infection and inflammation of the brain caused by Naegleria fowleri.
• The disease is diagnosed using specific laboratory tests available in only a few laboratories in the United States.

Because of the rarity of the infection and difficulty in initial detection, about 75% of diagnoses are made after the death of the patient.

PAM and Naegleria fowleri infection can be diagnosed in the laboratory by detecting:

• Naegleria fowleri organisms in cerebrospinal fluid (CSF), biopsy, or tissue specimens, or
• Naegleria fowleri nucleic acid in CSF, biopsy, or tissue specimens, or
• Naegleria fowleri antigen in CSF, biopsy, or tissue specimens.

Test Methods

Naegleria

The motile amebae can often be seen moving rapidly under a microscope when looking at a fresh sample of CSF. The amebae can also be stained with a variety of stains, such as Giemsa-Wright or a modified trichrome stain, for identification.

Antibody tests

A specific antibody to Naegleria fowleri can be used in conjunction with another antibody that deposits a chemical (immunohistochemistry [IHC]) or glows under specific types of light (indirect immunofluorescence [IIF]) to directly stain the amebic antigens in tissue.

DNA testing

Specific molecular tools can amplify DNA from the amebae in CSF or tissue to specifically identify if the amebae are present. Looking at strains or subtypes of Naegleria fowleri can be done, but little is known about the natural populations in the environment, which makes it difficult to interpret what the findings mean.

Culture

The amebae can be grown in culture to increase the likelihood of detecting the ameba by direct visualization or PCR. The sample is added to a growth plate covered in bacteria that can serve as a food source for Naegleria fowleri.

Histopathology of amebic meningoencephalitis due to Naegleria fowleri.

• The initial screening is accomplished by incubating the plate at a higher temperature (108°F/42°C) that kills most free-living amebae, while selecting for heat-loving (thermophilic) amebae, such as Naegleria fowleri or other amebae.
• This initial screen shows up as tracks made by an ameba as it moves across the plate eating the bacteria.
• If there are no amebae on the plate grown at the higher temperature, then Naegleria fowleri is not present.
• If heat-loving (thermophilic) amebae are present on the plate grown at the higher temperature, then these amebae undergo further specific testing to determine whether Naegleria fowleri is present since other free-living amebae can also be heat-loving (thermophilic).

Treatment

• Although most cases of primary amebic meningoencephalitis (PAM) are fatal, an investigational breast cancer and anti-leishmania drug, miltefosine, has shown some promise in combination with some of these other drugs.
• Miltefosine has shown ameba-killing activity against free-living amebae, including Naegleria fowleri, in the laboratory.
• After 35 years without a Naegleria survivor in the United States, during the summer of 2013, two children with Naegleria fowleri infection survived with miltefosine treatment.

Prevention & Control

• 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, 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.
• You cannot get infected from drinking water contaminated with Naegleria. You can only be infected when contaminated water goes up into your nose.

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