Naegleria fowleri, known colloquially as the ” brain eating amoeba,” is a genus species called Naegleria, which belongs to the Percolozoa phylum.It is a free- living, bacteria- eating amoeba that can be pathogenic and cause a fulminant( sudden and severe) brain infection called naegleriasis( PAM).This microorganism is usually found in warm water bodies such as lakes, rivers and hot springs.It is also found in the ground near warm water discharges from industrial plants and in unchlorinated or minimally chlorinated pools.It can be seen either in a flagellate or temporary flagellate stage.
Morphology of Naegleria fowleri
Naegleria fowleri is the only amoeba with three known morphological forms that is amoeboid trophozoites, flagellate( a flagella- like protozoa) and cysts.
Ameboid trophozoites form
The ameboid typical trophozoite of N.Fowleri appears elongated, measuring between 8 and 22 μmThe anterior end is generally wide, while the posterior end is usually narrowed.The sluggish motility of N.fowleri ameboid trophozoite is accomplished by blunt pseudopodia.The single nucleus contains a large karyosome, which is usually located centrally.There’s no peripheral chromatin.The cytoplasm of the N.fowleri ameboid trophozoite is granular and often contains vacuoles
The pear – shaped Naegleria fowleri flagellate is usually 7 to 15 μm in size.Two whip-like structures that support selected locomotive parasites known as flagella extend from the organism’s wide end.The typical motility is achieved by jerky movements or spinning. The nucleus is essentially the same as the ameboid trophozoite, a large central karyosome minus peripheral chromatin. Flagellate trophozoites usually have granular cytoplasms often containing vacuoles.
The cysts are usually round and have thick cell walls, measuring 9 to 12 μm in size.Naegleria fowleri cyst has only one nucleus, consisting of a large, centrally located karyosome without peripheral chromatin, similar to the two corresponding trophozoite stages.The cytoplasm is usually granular and usually contains vacuoles.
Life Cycle of Naegleria fowleri
The ameboid Naegleria fowleri trophozoites are the only form known to exist in humans.Ameboid trophozoites are replicated by simple binary fission.The ameboid trophozoites transform in vitro into flagellate trophozoites after being transferred from a tissue or culture to water.The flagellated trophozoites do not divide, but lose their flagella and return to the ameboid form in which reproduction is resumed.The cyst form is known to exist only in the outer environment.
It appears that the complete life cycle of Naegleria fowleri, which includes amoebic trophozoites that convert to cysts and flagellates and then return to amoebic trophozoites, occurs in the external environment.Humans contract this Amoeba mainly by swimming in contaminated water.
The ameboid trophozoites penetrate the human body through the nasal mucosa and often migrate into the brain, leading to rapid tissue destruction.Some infections may be caused by inhalation of dust infected with Naegleria fowleri.
Clinical symptoms of Naegleria fowleri infections
Patients suffering from Naegleria fowleri, which leads to colonization of the nasal passages, are usually asymptomatic.
Primary amebic meningoencephalitis (PAM)
Primary amoebic meningoencephalitis (PAM) occurs when the amoeboid trophozoites of Naegleria fowleri enter the brain and cause rapid tissue destruction.Patients may initially complain of
- sore throat
The symptoms of amoebic meningitis follow quickly, including stiff neck and seizures.In addition, the patient will often experience smell and taste alterations, blocked nose, and Kernig’s sign (defined as a diagnostic sign for meningitis, where the patient is unable to fully straighten his or her leg when the hip is flexed at 90 degrees because of hamstring stiffness).In untreated patients, death usually occurs 3 to 6 days after onset of treatment.Postmortem brain tissue samples from these patients show the typical amoeboid trophozoites of Naegleria fowleri.
Laboratory Diagnosis of Naegleria fowleri
Microscopic examination of cerebrospinal fluid (CSF) is the method of choice for recovery. Ameboid trophozoites penetrate the human body through the nasal mucosa and frequently migrate into the brain, causing rapid tissue destruction.Some infections may be caused by inhaling dust infected with Naegleria fowleri.
Treatment of Naegleria fowleri (amoebic meningitis treatment)
Unfortunately, drugs for the treatment of meningitis and amoebic infections are ineffective against Naegleria fowleri.However, there is evidence that rapid and aggressive treatment with amphotericin B can be beneficial to patients suffering from infections with Naegleria fowleri despite their known toxicity.
In rare cases, amphotericin B has also been shown to be effective in combination with rifampin or miconazole.Amphotericin B and miconazole damage the cell wall of Naegleria, inhibit the biosynthesis of ergosterol and lead to increased membrane permeability, which causes nutrients to escape from the cells.
Rifampicin inhibits RNA synthesis in the amoeba by binding to beta subunits of DNA-dependent RNA polymerase, which in turn blocks RNA transcription. A person can survive if signs are detected early, and if this is not the case, PAM almost always leads to death.
Prevention and Control of Naegleria fowleri
Due to the large number of potentially infected waters, complete eradication of Naegleria fowleri is highly unlikely.Setting signs beyond the limits of known sources of contamination and educating physicians and the public can help reduce infection rates.
It is also important that swimming pools and whirlpools are sufficiently chlorinated.Cracks in the walls of pools, whirlpools and bathtubs should be repaired immediately to avoid possible sources of contamination.
Notes of Interest and New Trends
The first case of PAM was reported by Carter and Fowleri, for whom the amoeba was named in Australia in 1965 and by Butt and Patras in the USA in 1966.
A remarkable species of Naegleria that could potentially infect humans in the future is known as Naegleria australiensis.This organism exists in the environment in Asia, Australia, Europe and the United States.Naegleria australiensis has been shown to be pathogenic in mice exposed to these parasites by intranasal instillation.
In recent years a number of methods have been investigated to classify, identify and specify Naegleria.These laboratory techniques include PCR assay, monoclonal antibody testing, flow cytometry and DNA hybridization.In addition, a method to support taxonomic classification, known as DNA restriction fragment length polymorphism (RFLP), was investigated.The results of all previous tests were favourable.However, further studies were recommended.