The Pathology of the Brain Eating Amoeba Naegleria fowleri

Abstract

The genus Naegleria is a taxonomic subfamily consisting of 47 free-living amoebae. The genus can be found in warm aqueous or soil habitats worldwide. The species Naegleria fowleri is probably the best-known species of this genus. As a facultative parasite, the protist is not dependent on hosts to complete its life cycle. However, it can infect humans by entering the nose during water contact, such as swimming, and travel along the olfactory nerve to the brain. There it causes a purulent meningitis (primary amoebic meningoencephalitis or PAME). Symptoms are severe and death usually occurs within the first week. PAME is a frightening infectious disease for which there is neither a proven cure nor a vaccine. In order to contain the disease and give patients any chance to survival, action must be taken quickly. A rapid diagnosis is therefore crucial. PAME is diagnosed by the detection of amoebae in the liquor and later in the cerebrospinal fluid. For this purpose, CSF samples are cultured and stained and finally examined microscopically. Molecular techniques such as PCR or ELISA support the microscopic analysis and secure the diagnosis.

Keywords: Amoebic; Nasal infections; Parasites; Protozoa; Tropical medicine.

Fig. 1

Naegleria fowleri

Fig. 2

Simplified phylogenetic tree according to the 6-kingdom model of Woese et al. [109]. The cross-branches represent endosymbiosis events

Fig. 3

Forms of Naegleria fowleri. Left: Cyst; middle: Trophozoite; right: Flagellate

Fig. 4

Warning sign from the United States. Alachua County, Florida

Fig. 5

Life cycle of Naegleria fowleri. ©Centers for disease control and prevention, all rights reserved

Fig. 6

Infected brain from a PAM patient. The whole brain is shown. Extensive hemorrhage and necrosis is present, mainly in the frontal cortex. ©Centers for disease control and prevention, all rights reserved

Fig. 7

Infected brain from a PAM patient. A brain section is shown. Focal hemorrhage and necrosis in frontal cortex is visible. ©Centers for disease control and prevention, all rights reserved

Fig. 8

Cytospin of fixed CSF showing Giemsa-Wright stained trophozoite of Naegleria fowleri (arrow) amidst polymorphonuclear leukocytes and some lymphocytes. The nucleus and nucleolus can be seen within the trophozoite. Magnification: 1000x. ©Centers for disease control and prevention, all rights reserved

Fig. 9

A section through the cerebral portion of the brain of a PAM patient stained with hematoxylin and eosin showing large accumulations of trophozoites of Naegleria fowleri and destruction of the normal architecture of the brain tissue. Cysts are not seen. Magnification: 100x. Inset: Higher magnification (1000x) of Naegleria fowleri trophozoites (arrows) showing characteristic nuclear morphology. ©Centers for disease control and prevention, all rights reserved