Free Living Amebic Infections
[Acanthamoeba spp.] [Balamuthia mandrillaris] [Naegleria fowleri] [Sappinia spp.]
Free-living amebae belonging to the genera Acanthamoeba, Balamuthia, Naegleria and Sappinia are important causes of disease in humans and animals. Naegleria fowleri produces an acute, and usually lethal, central nervous system (CNS) disease called primary amebic meningoencephalitis (PAM). Acanthamoeba spp. and Balamuthia mandrillaris are opportunistic free-living amebae capable of causing granulomatous amebic encephalitis (GAE) in individuals with compromised immune systems. Sappinia pedata has been implicated in a case of amebic encephalitis.
Acanthamoeba spp. cysts.
Acanthamoeba spp. trophozoites.
Balamuthia mandrillaris cysts.
Balamuthia mandrillaris trophozoites.
Naegleria fowleri cysts.
Naegleria fowleri trophozoites.
Sappinia spp. cysts and trophozoites.
Indirect immunofluorescence (IIF) assay for free-living amebic infections.
Gross pathology images in free-living amebic infections.
In Naegleria infections, the diagnosis can be made by microscopic examination of cerebrospinal fluid (CSF). A wet mount may detect motile trophozoites, and a Giemsa-stained smear will show trophozoites with typical morphology. In Acanthamoeba infections, the diagnosis can be made from microscopic examination of stained smears of biopsy specimens (brain tissue, skin, cornea) or of corneal scrapings, which may detect trophozoites and cysts. Confocal microscopy or cultivation of the causal organism, and its identification by direct immunofluorescent antibody, may also prove useful. An increasing number of PCR-based techniques (conventional and real-time PCR) have been described for detection and identification of free-living amebic infections in the clinical samples listed above. Such techniques may be available in selected reference diagnostic laboratories.
A real-time PCR was developed at CDC for identification of Acanthamoeba spp., Naegleria fowleri, and Balamuthia mandrillaris in clinical samples.1 This assay uses distinct primers and TaqMan probes for the simultaneous identification of these three parasites.
More on: TaqMan real-time PCR
- Qvarnstrom Y, Visvesvara GS, Sriram R, da Silva AJ. Multiplex real-time PCR assay for simultaneous detection of Acanthamoeba spp., Balamuthia mandrillaris, and Naegleria fowleri. J Clin Microbiol 2006;44(10):3589-3595.
DPDx is an education resource designed for health professionals and laboratory scientists. For an overview including prevention and control visit www.cdc.gov/parasites/.