|the stages flagellate, trophozoite and cyst (seen from upper left to lower left to right) of Naegleria fowleri|
Naegleria fowleri is a species of the genus Naegleria, belonging to the phylum Percolozoa. It is a free-living pathogenic protist that causes the disease naegleriasis also known as primary amoebic meningoencephalitis.
This microorganism is typically found in bodies of warm freshwater ponds, lakes, rivers, and hot springs. It is also found in the soil, near warm-water discharges of industrial plants, and in poorly or unchlorinated swimming pools, in an amoeboid or temporary flagellate stage. There is no indication of N. fowleri living in salt water.
N. fowleri is found in warm freshwater ponds, lakes and rivers, and in the very warm water of hot springs. It was first discovered in 1965, and first identified in Australia. N. fowleri occurs in three forms – as a cyst, a trophozoite (ameboid), and a flagellate. It does not form a cyst in human tissue. Only the amoeboid trophozoite stage exists in human tissue. The flagellate form can exist in the cerebrospinal fluid (CSF).
Trophozoites encyst due to unfavorable conditions. Factors that induce cyst formation include a lack of food, overcrowding, desiccation, accumulation of waste products, and cold temperatures. N. fowleri has been found to encyst at temperatures below 10°C (50°F).
This reproductive stage of the protozoan organism, which transforms near 25°C (77°F) and grows fastest around 42°C (106.7°F), proliferates by binary fission. The trophozoites are characterized by a nucleus and a surrounding halo. They travel by pseudopodia, temporary round processes which fill with granular cytoplasm. The pseudopodia form at different points along the cell, thus allowing the trophozoite to change directions. In their free-living state, trophozoites feed on bacteria. In tissues, they phagocytize red blood cells and white blood cells and destroy tissue.
This biflagellate form occurs when trophozoites are exposed to a change in ionic concentration, such as placement in distilled water. (The flagellate form does not exist in human tissue, but can exist in the cerebrospinal fluid). The transformation of trophozoite to flagellate occurs within a few hours.
N. fowleri can cause a lethal infection of the brain called naegleriasis (also known as primary amoebic meningoencephalitis (PAM), amebic encephalitis, or Naegleria infection). Infections can occur when water containing N. fowleri is breathed in through the nose, where it then invades through nasal tissue and olfactory nerve tissue to enter the brain. Though coined with the term 'brain-eating amoeba', the patient dies more due to the complications of acute inflammatory reaction (raised intracranial pressure) than the destructive enzymes secreted by N. fowleri. 
- "Brain-eating-amoeba". http://www.webmd.com/brain/brain-eating-amoeba.
- Marciano-Cabral, F (1988). "Biology of Naegleria spp". Microbiological reviews 52 (1): 114–33. PMC 372708. PMID 3280964.
- Chang, SL (1978). "Resistance of pathogenic Naegleria to some common physical and chemical agents". Applied and environmental microbiology 35 (2): 368–75. PMC 242840. PMID 637538.
- Baig AM. Pathogenesis of amoebic encephalitis: Are the amoebae being credited to an 'inside job' done by the host immune response? Acta Trop. 2015 Aug;148:72-6. doi: 10.1016/j.actatropica.2015.04.022. Epub 2015 Apr 27. Review. PubMed PMID 25930186.