Brain-Eating Amoeba (Naegleriasis)

Overview

Naegleria fowleri is a species of amoeba that is notorious for its ability to afflict humans with a rare and deadly disease known as naegleriasis by aggressively attacking the central nervous system. This single-celled microorganism normally thrives in warm, stagnant freshwater environments such as lakes, mud pools, hot springs and even in the soil.

Its diet typically consists of bacteria and yeast but when it comes into contact with humans and infects them, it begins to actively feed on brain tissue. The microbe’s ability to thrive in warm environments means that it can even survive any fever response mounted by the human body. Its ability to withstand and evade the human immune system makes N. fowleri a highly virulent pathogen. The infection cannot, however, spread from one human to another. It has not been possible to conduct clinical trials due to the sporadic incidence and rarity of naegleriasis. Hence, there is no known cure or vaccine and survival rates are very poor.

What Is Brain-Eating Amoeba or Naegleriasis?

Naegleriasis is a disease caused by infection with a species of amoeba known as Naegleria fowleri. It is also known as primary amoebic meningoencephalitis (PAM). The pathogen, usually present in a contaminated water source, enters the body through the nose.

Subsequently, it attaches itself to the olfactory nerve, travels to the frontal lobe of the brain and spreads throughout the brain, feeding voraciously on nervous tissue. This organism is believed to be particularly deadly because it has developed effective mechanisms for combating the human body’s immune response and also because it multiplies rapidly once it begins feeding on nervous tissue. The PAM, characterized by inflammation and hemorrhaging, progresses quickly in a matter of days and almost invariably ends in fatality.

How Does It Happen?

The direct cause of naegleriasis is infection with the disease-causing amoeba N. fowleri. Swimming in ponds, hot springs or insufficiently chlorinated swimming pools infested with this amoeba greatly increases the risk of contracting an infection and developing PAM. In a rare instance, infection was contracted after the individual underwent a baptism ceremony which involved ritual immersion in water which happened to be contaminated.

However, contact with N. fowleri is in fact far more common than the incidence of naegleriasis would indicate. This suggests that infection is not a necessary outcome of exposure to the microbe, although it is unclear why this is so. N. fowleri exists in trophozoite form or actively feeding form at warmer temperatures. Further, humans tend to engage in more water-based activities during the hotter months of the year. Hence, the incidence of naegleriasis is relatively higher in the summer season.

How Does The Brain-Eating Amoeba Affect The Brain?

The incubation period can last anywhere between two days and a fortnight from the time of infection. The onset of symptoms can even occur within 24 hours post infection. The pathogen first enters the body through the nose, attaches itself to the olfactory nerve and attacks the olfactory bulbs in the frontal part of the brain. It extends special feeding structures called food cups to ingest nervous tissue and releases substances that cause the breakdown or lysis of nerves. Naegleriasis typically manifests in the form of primary amoebic meningoencephalitis (PAM) which produces symptoms typical of progressive breakdown of nervous function:

• Loss of smell and taste.
• Fever.
• A severe headache.
• Nausea.
• Vomiting.
• The blurring of vision.
• The stiffness of neck muscles.
• Inability to concentrate.
• Inability to control body movement.
• Abnormal heart rhythm in rare instances.
• Mental confusion.
• Hallucinations.
• Seizures.

What Are The Complications?

The progress of naegleriasis is notoriously rapid and a patient can die within a week of the onset of symptoms. The pathogen multiplies quickly, feeding aggressively on nervous tissue, triggering an intense inflammatory response and causing hemorrhage.

As the disease runs its course the patient begins to experience hallucinations and seizures and eventually descends into a comatose state. The buildup of pressure within the cranium and rise in cerebrospinal fluid pressure is usually the direct cause of death. Unfortunately, in the absence of a viable treatment, fatality is the most likely outcome. Only in a few cases have patients been known to survive.

What Tests Can Help To Detect Brain-Eating Amoeba?

The primary site of N. fowleri pathogenicity is the brain. Magnetic resonance imaging (MRI) and computerized tomography (CT) reveals the swelling and hemorrhaging in this area. But these signs do not in themselves provide a clue as to the identity of the infectious agent. Cases of naegleriasis have sometimes been misinterpreted as bacterial or viral meningitis and in most instances, an accurate diagnosis of the true cause has only been made post-mortem.

N. fowleri exists in its active trophozoite form in the brain and cerebrospinal fluid. Ordinary blood tests and scans cannot reveal its presence. Therefore, if naegleriasis is suspected, an effective way to detect the pathogen in the patient’s body is through a procedure known as lumbar puncture which enables the extraction of a small sample of cerebrospinal fluid for testing. Biopsy of brain tissue specimens also reveals the presence of N. fowleri trophozoites.

Treatment and Prevention

Treatment – Swift diagnosis and treatment with specific antifungals may be useful. But recovery is rare. Hospitals most commonly treat brain-eating amoeba with the anti-fungal drug amphotericin. It is typically injected into the vein or in the space around the spinal cord. The antifungal drug kills the amoeba so that there can be no further damage. Miltefosine is a potentially life-saving experimental drug that helps treat people who are infected with the brain-eating amoeba virus.

Prevention 

• Do not dive, jump or swim in warm surface waters.
• Make sure that the swimming pool or spa that you are going to is clean and well kept.
• Keep sprinklers and hoses away from your nose.

References