Naegleria infection laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Laboratory Findings
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.
Microscopy
A: Naegleria fowleri trophozoites, cultured from cerebrospinal fluid. These cells have characteristically large nuclei with a large, dark staining karyosome. The amebae are very active and extend and retract pseudopods. Trichrome stain. From a patient who died from primary amebic meningoencephalitis in Virginia.
Naegleria fowleri trophozoite.jpg|left|Naegleria fowleri trophozoite]]
B: Naegleria fowleri trophozoite in spinal fluid. Trichrome stain. Note the typically large karyosome and the monopodial locomotion. Image contributed by Texas State Health Department.
Molecular Diagnosis
Real-Time PCR
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.