Lethal encounters: The evolving spectrum of amoebic meningoencephalitis

Abstract

The free-living amoebae are thermophilic organisms that may play an increasing role among diseases of a warming world. They are uncommon, accidental, yet high consequence pathogens, with differing pathologic syndromes. New prospects for diagnosis and life-saving treatment make early disease recognition imperative. We review the three most commonly diagnosed species that infect humans: Naegleria fowleri, Acanthamoeba species, and Balamuthia mandrillaris.

Keywords: Acanthamoeba; Ameba; Amoeba; Balamuthia; Encephalitis; Meningitis; Naegleria.

Fig. 1

Case-reports of Primary Amebic Meningoencephalitis by State of Exposure. https://www.cdc.gov/parasites/naegleria/state-map.html.

Fig. 2

Case-reports of PAM by Month of Illness Onset and Probable Water Exposure. https://www.cdc.gov/parasites/naegleria/graphs.html.

Fig. 3

Primary amoebic meningoencephalitis: Extensive exudate and hemorrhage of the frontal cerebral cortex [21]. CDC, public domain image. https://www.cdc.gov/parasites/naegleria/naegleria-fowleri-images.html#photos

Fig. 4

Naegleria fowleri trophozoite: CSF cytospin sediment stained with Wright-Giemsa, 1000x magnification [20]. CDC, public domain image.

Fig. 5

Naegleria fowleri trophozoite: A wet mount of (arrow) in CSF. Image used with permission of the author, Francine Marciano-Cabral [24].

Fig. 6

Acanthamoeba trophozoite: Scanning electron micrograph, demonstrating spike-like pseudopodia. Image used with permission from American Society for Microbiology.

Fig. 7

Granulomatous meningoencephalitis due to Acanthamoeba: Cysts observed in brain tissue (arrows) stained with hematoxylin and eosin (public domain image, CDC). https://www.cdc.gov/dpdx/freeLivingAmebic/index.html.

Fig. 8

Granulomatous meningoencephalitis: Autopsy specimen demonstrating extensive necrotizing, mixed inflammatory, vasculitic, and granulomatous encephalitis. CDC, public domain image. Credited to Cook Children’s Hospital, Fort Worth, Texas.

Fig. 9

Sentinel ulcer of Balamuthia infection: Nasal sore that preceded this patient’s GAE by several months [50]. Image used with permission of Elsevier Ltd.

Fig. 10

Balamuthia mandrillaris: Hematoxylin and eosin stain of brain tissue demonstrating viable trophozoites (arrows) [50]. Image used with permission of Elsevier Ltd.

Fig. 11

Skin lesion of Balamuthia infection: Indurated violaceous or indurated plaque and ulceration seen with Balamuthia mandrillaris infection [56]. Image used with permission of Elsevier Ltd.

Fig. 12

Balamuthia mandrillaris imaging: Ring-enhancing lesions on MRI of the brain [50]. Images used with permission of Elsevier Ltd.