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Naegleria fowleri

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

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

  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.
  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.
  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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