Free living amoebic infections causing CNS disease - diagnostic techniques

Abstract

Free-living amoebae belonging to the genera Acanthamoeba, Balamuthia and Naegleria are important causes of disease in humans. Naegleria fowleri produces an acute, and usually lethal, central nervous system (CNS) disease called primary amoebic meningoencephalitis (PAM). Acanthamoeba spp. and Balamuthia mandrillaris are opportunistic free-living amoebae capable of causing a more chronic granulomatous amoebic encephalitis (GAE), often in immunocompromised individuals. In Naegleria infections, the diagnosis can be made by microscopic examination of cerebrospinal fluid (CSF) demonstrating motile trophozoites, and a Giemsa-stained smear will show trophozoites with typical morphology. In Acanthamoeba and Balamuthia infections, organisms are usually not present in CSF and the diagnosis can be made from microscopic examination of stained smears of biopsy specimens (brain tissue, skin, cornea) containing both trophozoites and cysts. Identification by direct immunofluorescent antibody may also prove useful. PCR-based techniques have been described for free-living amoebic infections in clinical samples and a multiplex real-time PCR has been adopted 1 at Sullivan Nicolaides Pathology which has proved useful both for detection and identification of the species in two locally acquired cases due to Balamuthia mandrillaris and Naeglaria fowleri .