Morphologic and Molecular Identification of Naegleria dunnebackei n. sp. Isolated from a Water Sample



    1. Division of Parasitic Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA, and
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    1. Protozoology Laboratory, Scientific Institute Public Health, Brussels, Belgium, and
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    • 1Present address: Research unit for Tropical Diseases, Christian de Duve Institute of Cellular Pathology, Avenue Hippocrate, 74-75, B1200 Brussels, Belgium.


    1. Department of Microbiology and Immunology, Virginia Commonwealth University School of Medicine, Richmond, Virginia, USA, and
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    1. California Department of Health Services, Viral and Rickettsial Disease Laboratory, Richmond, California, USA
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Corresponding Author: G. S. Visvesvara, Division of Parasitic Diseases, M.S.-F-36, Chamblee Campus, Bldg. 109, Centers for Disease Control and Prevention, 4770 Buford Highway NE, Atlanta, GA 30341-3724—Telephone number: 770-488-4417; Fax number: 770-488-4253; e-mail:


ABSTRACT. Naegleria dunnebackei n. sp., a new species of the free-living amoeboflagellate Naegleria, is described in this report. The organism was isolated from a water sample taken from drinking troughs associated with cases of primary amoebic meningoencephalitis in cattle at a ranch in southern California. The isolate grew at, but not above 37°C, and did not kill young mice upon intranasal inoculation suggesting that it was not pathogenic. The new species combines morphological features of non-pathogenic Naegleria gruberi and pathogenic Naegleria fowleri. The trophic amoeba resembled other members of the genus, with a prominent vesicular nucleus and mitochondria with discoidal cristae; a Golgi apparatus was not observed by electron microscopy. The cyst stage had pores in the wall typical of those seen in pathogenic N. fowleri. Upon suspension in distilled water, amoebae transformed into temporary, non-feeding flagellates, mostly with two anterior flagella but occasionally with four. The rationale for its description as a new species was based upon sequencing of the 5.8S rDNA and internal transcribed spacers of the amoeba, which is similar to but not identical to that of Naegleria gallica, differing from that organism's DNA by six base pairs. Virus-like elements were found in the cytoplasm of trophic amoebae, often in association with crystalloids, and may be the cause of lysis of amoebae in culture.