Naegleriasis (Brain-Eating Amoeba Infection)

What is Brain-Eating Amoeba?

Brain-eating amoeba or Naegleria fowleri is a type of amoeba that belongs to the Naegleria genus family. It is a single-celled organism found all around the world. It is a heat-loving amoeba that can be commonly found in water bodies like fresh-water rivers and lakes, and in the soil.

Naegleria fowleri is known as brain-eating amoeba because it causes a rare fatal brain infection in humans. The disease is commonly called Primary Amoebic Meningoencephalitis (PAM) or Naegleriasis. The first PAM infection was reported from Australia. The amoeba turned out to be a new species and was named Naegleria fowleri after one of the authors of the report, M. Fowler.

What are the Causes of Naegleriasis?

Although millions of people are exposed to Naegleria fowleri due to its widespread occurrence actual infection is rare. The exact reason for the low infection rate is not known. The primary mechanism by which the amoeba infects humans is via the nasal passage.

The amoeba enters the body only through nasal exposure to contaminated water. It then passes over to the brain along the pathway of the olfactory nerves - the nerves that carry the smell signals from the nose to the brain. Once it reaches the brain, it causes inflammation and starts to destroy the tissues of the brain.

Mostly humans are exposed to the amoeba through water-related activities. Generally, the exposure is from swimming pools where the water temperature is warmer. The infection is not contagious and also it is not present in clean and properly disinfected water. Also, people do not become infected by drinking contaminated water.

What are the Symptoms and Signs of Naegleriasis?

Primary Amoebic Meningoencephalitis (PAM) is a serious infection of the central nervous system and its covering tissues. It causes inflammation and destruction of the brain tissues. Symptoms start appearing after 1-9 days of nasal exposure to Naegleria-containing water. People die 1-18 days after the onset of the symptoms. Most of the symptoms resemble the symptoms of bacterial meningitis disease and is therefore difficult to detect. The disease progresses rapidly and the victim may die within a week. Signs and symptoms of the infection can be divided into two stages namely, initial stage and advanced stage.

Initial stage

The symptoms usually develop within two days from the Naegleria exposure and include:

• Fever
• Nausea and vomiting
• Severe frontal headache

Advanced stage

A few days later, the infected person may show these signs:

• Seizures
• Hallucinations
• Coma
• Stiff neck

How is Naegleriasis Diagnosed?

The rarity of the infection makes it difficult to diagnose Naegleriasis in the initial stages. About 75% of people with the disease are diagnosed only after their death. The most common methods used to detect changes in the human brain are MRI and CT Scan Imaging techniques. The Naegleria fowleri organisms, DNA or antigen can also be detected in the cerebrospinal fluid (CSF), biopsy, or tissue specimens of the infected persons. The CSF is the fluid that surrounds the brain and spinal cord. A sample of the fluid is obtained through a procedure called spinal tap.

The methods followed to test Naegleria fowleri include the following:

• By looking at a fresh sample of the CSF fluid under a microscope, the presence of the motile amoeba can be detected. Different stains like Giemsa-Wright or a modified trichrome stain are used for identifying it accurately.
• The antigen of the amoeba can be detected using tests like indirect immunofluorescence and immunohistochemistry tests.
• Polymerize Chain reaction amplifies the DNA of the amoeba present in the CSF fluid or tissues by which the presence of the organism can be detected.
• A culture is done at 108�F/42�C, at which temperature amoeba like Naegleria fowleri survive. The surviving amoeba undergo further testing as other thermophilic amoeba may also be present. Culturing can increase the likelihood of detecting the amoeba by direct visualization or PCR. Then these samples obtained from water bodies are also tested as above.

How do you Treat Brain-Eating Amoeba?

Several drugs like amphotericin B, azithromycin, fluconazole and rifampin have been tried for the treatment of Naeglerisis. However, it is not known how effective these treatments are since most patients have not survived following treatment.

Recently the Centers for Disease Control and Prevention (CDC) has introduced a drug called miltefosine (Impavido) that appears to be effective for treating Naeglerisis. Currently, two survivors of the disease are documented who have been treated with miltefosine along with other medications.

Prevention of Naegleriasis

The only way to prevent Naegleriasis infection is by staying away from water-related activities. However, if a swimming pool is clean and well maintained, it is unlikely to have the amoebae. It is better to use some kind of protective equipment like nose clips to cover the nose before entering fresh water bodies. Sediments should not be disturbed while swimming in shallow warm waters. One should limit their activities in such a way that water does not enter into the nose. These are some common practices that can be followed to be safe from exposure to this organism.

References:

1. CDC at Work: Naegleria fowleri - (http://www.cdc.gov/parasites/naegleria/cdc-at-work.html)
2. Naegleria infection - (http://www.mayoclinic.org/diseases-conditions/naegleria-infection/basics/symptoms/con-20034093)

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