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.

Taxonomy

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

Biology

Life cycle of N. fowleri and other free-living Amebae. Click to enlarge and view caption.

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

• Trophozoite: Infective stage characterized by the presence of contractile vacuoles. Organisms contain lobopodia for motility and reproduce by binary fission. It uses a unique food-cup 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: A resistant stage whereby the organism 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

• The structure of N. fowleri is based on the life cycle stage. In its trophozoite infective form, the organism appears ameboid with characteristic contractile vacuoles that differentiate it from other organisms.

Tropism

• N. fowleri
• 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:

• Soil
• Swimming pools
• Home showers
• Sewers
• Cooling towers

External links

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