Naegleria fowleri

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This page is about microbiologic aspects of the organism(s). For clinical aspects of the disease, see Primary amoebic meningoencephalitis.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Naegleria fowleri (also known as the brain eating amoeba) is a ubiquitous, free living amoeba typically grows contaminated, warm (25–35 °C / 77–95 °F), fresh water (e.g. lakes or hot springs). It belongs to a group called the Percolozoa or Heterolobosea. N. fowleri is transmitted to the humans through the nose when individuals swim/dive in lakes. Drinking contaminated water, however, does not result in transmission. N. fowleri causes primary amebic meningoencephalitis (PAM), a rare disease whereby N. fowleri invades the human central nervous system through the cibriform plate and causes fulminant fatal meningoencephalitis in the majority of cases.^[1]^[2]

Taxonomy

Phylum = Percolozoa
Class = Heterolobosea
Order = Schizopyrenida
Family = Vahlkampfiidae
Genus = Naegleria
Species = N. fowleri
Binomial = Naegleria fowleri

Biology

Shown below is an the life cycle of N. fowleri:

N. fowleri grows ideally at 42 °C (108 °F), but it can tolerate temperatures as high as 45 °C (113 °F).^[3]
There are 3 morphological stages in the life cycle of Naegleria fowleri:^[3]

Trophozoite: 10-30 mu - Infective stage characterized by the presence of contractile vacuoles. It reproduces by binary fission. It uses pseudopods structure to ingest other organisms, red blood cells, and white blood cells.
Flagellate: A temporary stage when the organism is exposed to changes in pH (e.g. from culture to distilled water).
Cyst: 7-14 μm - A resistant stage whereby the organism is protected by a dense cell wall that can tolerate harsh environments, such as cold weather or states of low nutrition. Cysts may be transmitted to the human host and transformed into trophozoites.

Structure

N. fowleri is a facultatively aerobic, heterotrophic organism.^[4]
In its trophozoite form, it may appear either ameboid or flagellated.
It contains the following structures for survival and growth:

Mitochondria
Pseudopods
Flagella
Contractile vacuoles

Tropism

N. fowleri invades the central nervous system (highly oxygenated environment) and causes meningoencephalitis.^[3]
N. fowleri is transmitted to humans via the nasal cavity into the cribriform plate.
It invades the subarachnoid spaces by migrating along the mesaxonal of unmyelinated olfactory nerves.
When it reaches the subarachnoid space, it may then disseminate to other tissues of the central nervous system.
It migrates along the mesaxonal spaces of unmyelinated

Natural Reservoir

The natural reservoir of N. fowleri are typically fresh water lakes and hot springs.
N. fowleri has also been isolated from:^[4]

Soil
Swimming pools
Home showers
Sewers
Cooling towers

References

↑ "The Centers for Disease Control and Prevention, Division of Parasitic Diseases - Naegleria Infection Fact Sheet". Retrieved 2007-10-09.
↑ "6 Die From Brain-Eating Amoeba in Lakes". Retrieved 2007-10-03.
↑ ^3.0 ^3.1 ^3.2 John DT (1982). "Primary amebic meningoencephalitis and the biology of Naegleria fowleri". Annu Rev Microbiol. 36: 101–23. doi:10.1146/annurev.mi.36.100182.000533. PMID 6756287.
↑ ^4.0 ^4.1 Park JS, Simpson AG, Lee WJ, Cho BC (2007). "Ultrastructure and phylogenetic placement within Heterolobosea of the previously unclassified, extremely halophilic heterotrophic flagellate Pleurostomum flabellatum (Ruinen 1938)". Protist. 158 (3): 397–413. doi:10.1016/j.protis.2007.03.004. PMID 17576098.

External links

Naegleria Infection fact sheet from the website of the Centers for Disease Control and Prevention

[1] "The Centers for Disease Control and Prevention, Division of Parasitic Diseases - Naegleria Infection Fact Sheet". Retrieved 2007-10-09.

[2] "6 Die From Brain-Eating Amoeba in Lakes". Retrieved 2007-10-03.

[pmid6756287-3] 3.0 ^3.1 ^3.2 John DT (1982). "Primary amebic meningoencephalitis and the biology of Naegleria fowleri". Annu Rev Microbiol. 36: 101–23. doi:10.1146/annurev.mi.36.100182.000533. PMID 6756287.

[pmid17576098-4] 4.0 ^4.1 Park JS, Simpson AG, Lee WJ, Cho BC (2007). "Ultrastructure and phylogenetic placement within Heterolobosea of the previously unclassified, extremely halophilic heterotrophic flagellate Pleurostomum flabellatum (Ruinen 1938)". Protist. 158 (3): 397–413. doi:10.1016/j.protis.2007.03.004. PMID 17576098.

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