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Naegleria Infection Workup

  • Author: Subhash Chandra Parija, MBBS, MD, PhD, FRCPath, DSc; Chief Editor: Mark R Wallace, MD, FACP, FIDSA  more...
Updated: Nov 23, 2015

Laboratory Studies

The diagnosis of primary amebic meningoencephalitis (PAM) is always parasitic and is based on detection and identification of N fowleri trophozoites in the CSF or brain biopsy samples.


The CSF is the specimen of choice for demonstration of the amebae.

Direct wet-mount microscopy

The CSF is centrifuged at 150 xg for 5 minutes. The supernatant is aspirated, and the sediment is suspended in the remaining fluid. A drop of sediment suspension is kept on a slide and mounted with a coverslip and is examined with compound light microscopy using 10X and 40X objectives. The specimen is best examined with phase contrast microscopy. This may show trophozoites with lobopodia extension and retraction.

The amebae are detected based on their active directional movements. Close observation is important because PAM can be diagnosed based on the observation of trophozoites; however, these have been confused with WBCs in reported cases. Cyst and flagellated stages are not found in CSF samples; if both cysts and trophozoites are found in CSF, it is highly suggestive of Acanthamoeba infection, ruling out Naegleria PAM.

A few drops of CSF are mixed with 1 mL of distilled water and examined after 1 hour for flagellated forms typical of N fowleri. Trophozoites of N fowleri measure around 10-25 μm, with typical limacine/eruptive amoeboid movement, indicating a positive enflagellation test result.[28]

Examination of stained CSF smear

CSF Gram stain findings are usually negative. RBCs are present. Wright-Giemsa–stained CSF may show trophozoites with large karyosome and may show a contractile vacuole. Direct fluorescent antibody staining of CSF smears is useful for demonstrating N fowleri in the CSF.


Naegleria species can be readily cultivated on either nonnutrient agar or agar media containing low concentrations of nutrients (eg, peptone 0.05%, yeast extract 0.05%, glucose 0.1%) in the presence of living or killed bacteria or in defined axenic media, as proposed by Chang et al and Nerad et al, among others. A nonnutrient/low-nutrient agar is chosen to prevent overgrowth of bacteria.[29]  In general, the bacteria of choice include nonmucoid strains of Klebsiella pneumoniae, Enterobacter species (Enterobacter aerogenes and Enterobacter cloacae), and Escherichia coli. After several days, the plate is microscopically inspected; Naegleria cysts are identified by trails left by migrating amebae in the lawn of the bacteria. Various molecular methods can be used for final confirmation of the identity of the species.


Serologic testing has no role in the diagnosis of acute PAM, since little time is available from onset to death to mount an antibody response. In one survivor, detectable antibody persisted for more than 4 years.

Molecular diagnosis

PCR is available at some research sites using numerous primers. Molecular characterization of strains is also useful in tracking infections to a source and in recognizing potential risks for swimmers or bathers in particular locales. A species-specific DNA probe is available to identify N fowleri in environmental samples, followed by restriction fragment length polymorphism (RFLP) analyses of whole-cell DNA for confirmation. Epidemiologic typing of N fowleri was used in an analysis of the 5.8S rRNA gene and the internal transcribed spacer (ITS) of clinical isolates. In a study performed in the United States, a rapid, sensitive, and specific assay for the detection of N fowleri was developed using Mp2C15 probe in a nested PCR assay format.[30] A nested PCR assay has also been applied to detect the presence of the parasite in domestic water sources.[31]

Recently, flow cytometry has been used for the diagnosis of N fowleri infection.[32] Flores et al evaluated flow cytometry and monoclonal antibodies in differentiating Naegleria fowleri from Acanthamoeba species.[33]

Lately, a real-time PCR using hybridization fluorescent-labelled probes, targeting the N fowleri Mp2Cl5 gene sequence, has been developed. The reaction detection limit in their study was 1 copy of the Mp2Cl5 DNA sequence.[34]

Visvesvara has reported the development of a multiplex real-time PCR that could simultaneously look for Naegleria, Acanthamoeba, and Balamuthia species in a single specimen, thus reducing the time for diagnosis. This is especially useful as infection with any of the 3 amoebae could have clinical presentations indistinguishable from each other.[35]  Similarly, Qvarnstrom et al described a TaqMan-based multiplex real-time PCR that targets the 18S rRNA gene in the detection of N fowleri, Acanthamoeba species, and Balamuthia mandrillaris.[36]


Both immunofluorescence and immunoperoxidase methods are useful for demonstrating N fowleri trophozoites in the histologic sections of the brain biopsy samples.


Imaging Studies

Head CT scanning yields nonspecific findings, showing a loss of the subarachnoid space and diffuse gray material enhancement.


Other Tests

CSF studies show the following:

  • Sanguinopurulent or bloody CSF, showing a nonspecific polymorphonuclear (PMN) neutrophil – predominant neutrophilia
  • Increased opening pressure
  • PMN pleocytosis
  • Elevated RBC count or frank hemorrhagic CSF
  • Normal-to-low CSF glucose level
  • Elevated protein level


Lumbar puncture: Wet-mount examination of CSF is the main diagnostic tool in PAN.


Histologic Findings

N fowleri infection produces lesions mainly in the base of the brain, brain stem, and cerebellum. The olfactory mucosa and bulbs are the most commonly affected areas. The lesions consist of an acute necrotizing meningoencephalitis associated with moderately purulent exudates. Only trophozoites are found in the CNS lesions, not cysts

Contributor Information and Disclosures

Subhash Chandra Parija, MBBS, MD, PhD, FRCPath, DSc Director-Professor of Microbiology, Head of Department of Microbiology, Jawaharlal Institute, Postgraduate Medical Education and Research, India

Subhash Chandra Parija, MBBS, MD, PhD, FRCPath, DSc is a member of the following medical societies: Royal College of Pathologists, Indian Society for Parasitology, Indian Medical Association, National Academy of Medical Sciences (India), Indian Association of Medical Microbiologists, Indian Association of Biomedical Scientists, Indian Association of Pathologists and Microbiologists, Indian Academy of Tropical Parasitology

Disclosure: Received salary from Jawaharlal Institute of Postgraduate Medical education & Research , Pondicherry , India for employment.


Michael Stuart Bronze, MD David Ross Boyd Professor and Chairman, Department of Medicine, Stewart G Wolf Endowed Chair in Internal Medicine, Department of Medicine, University of Oklahoma Health Science Center; Master of the American College of Physicians; Fellow, Infectious Diseases Society of America

Michael Stuart Bronze, MD is a member of the following medical societies: Alpha Omega Alpha, American Medical Association, Oklahoma State Medical Association, Southern Society for Clinical Investigation, Association of Professors of Medicine, American College of Physicians, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Thomas M Kerkering, MD Chief of Infectious Diseases, Virginia Tech Carilion School of Medicine

Thomas M Kerkering, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians, American Public Health Association, American Society for Microbiology, American Society of Tropical Medicine and Hygiene, Infectious Diseases Society of America, Medical Society of Virginia, Wilderness Medical Society

Disclosure: Nothing to disclose.

Chief Editor

Mark R Wallace, MD, FACP, FIDSA Clinical Professor of Medicine, Florida State University College of Medicine; Clinical Professor of Medicine, University of Central Florida College of Medicine

Mark R Wallace, MD, FACP, FIDSA is a member of the following medical societies: American College of Physicians, American Medical Association, American Society for Microbiology, Infectious Diseases Society of America, International AIDS Society, Florida Infectious Diseases Society

Disclosure: Nothing to disclose.

Additional Contributors

Daniel R Lucey, MD, MPH, MD, MPH 

Daniel R Lucey, MD, MPH, MD, MPH is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians

Disclosure: Nothing to disclose.


Barnett Gibbs, MD Assistant Chief, Department of Clinical Trials, Walter Reed Army Institute of Research, Infectious Disease Service, National Capital Consortium; Assistant Professor of Medicine, Uniformed Services University of the Health Sciences

Disclosure: Nothing to disclose.

Diane H Johnson, MD Assistant Director, Assistant Professor, Department of Internal Medicine, Division of Infectious Diseases, Winthrop-University Hospital, State University of New York at Stony Brook School of Medicine

Diane H Johnson, MD is a member of the following medical societies: American College of Physicians, American Medical Association, American Medical Women's Association, American Society for Microbiology, and Infectious Diseases Society of America

Disclosure: Nothing to disclose.

  1. Yadav D, Aneja S, Dutta R, Maheshwari A, Seth A. Youngest survivor of naegleria meningitis. Indian J Pediatr. 2013 Mar. 80(3):253-4. [Medline].

  2. Schuster FL. Cultivation of pathogenic and opportunistic free-living amebas. Clin Microbiol Rev. 2002 Jul. 15(3):342-54. [Medline].

  3. Centers for Disease Control and Prevention. Primary amebic meningoencephalitis--Arizona, Florida, and Texas, 2007. MMWR Morb Mortal Wkly Rep. 2008 May 30. 57(21):573-7. [Medline].

  4. Parija SC. Textbook of Medical Parasitology. Protozoology and Helminthology. 4 ed. New Delhi: All India Publishers and Distributers; 2013.

  5. Cervantes-Sandoval I, Serrano-Luna Jde J, Garcia-Latorre E, Tsutsumi V, Shibayama M. Mucins in the host defence against Naegleria fowleri and mucinolytic activity as a possible means of evasion. Microbiology. 2008 Dec. 154(Pt 12):3895-904. [Medline].

  6. Jung SY, Kim JH, Song KJ, Lee YJ, Kwon MH, Kim K. Gene silencing of nfa1 affects the in vitro cytotoxicity of Naegleria fowleri in murine macrophages. Mol Biochem Parasitol. 2009 May. 165(1):87-93. [Medline].

  7. Yoder JS, Eddy BA, Visvesvara GS, Capewell L, Beach MJ. The epidemiology of primary amoebic meningoencephalitis in the USA, 1962-2008. Epidemiol Infect. 2010 Jul. 138(7):968-75. [Medline].

  8. Yoder JS, Straif-Bourgeois S, Roy SL, Moore TA, Visvesvara GS, Ratard RC. Primary amebic meningoencephalitis deaths associated with sinus irrigation using contaminated tap water. Clin Infect Dis. 2012 Nov. 55(9):e79-85. [Medline].

  9. Jamerson M, Remmers K, Cabral G, Marciano-Cabral F. Survey for the presence of Naegleria fowleri amebae in lake water used to cool reactors at a nuclear power generating plant. Parasitol Res. 2009 Apr. 104(5):969-78. [Medline].

  10. Marciano-Cabral F, Jamerson M, Kaneshiro ES. Free-living amoebae, Legionella and Mycobacterium in tap water supplied by a municipal drinking water utility in the USA. J Water Health. 2010 Mar. 8(1):71-82. [Medline].

  11. Laseke I, Korte J, Lamendella R, Kaneshiro ES, Marciano-Cabral F, Oerther DB. Identification of Naegleria fowleri in warm ground water aquifers. J Environ Qual. 2010 Jan-Feb. 39(1):147-53. [Medline].

  12. Herriman R. California reports 7th ever Naegleria fowleri case in Inyo County woman. Outbreak News Today. 2015.

  13. Kaushal V, Chhina DK, Ram S, Singh G, Kaushal RK, Kumar R. Primary amoebic meningoencephalitis due to Naegleria fowleri. J Assoc Physicians India. 2008 Jun. 56:459-62. [Medline].

  14. Khanna V, Khanna R, Hebbar S, Shashidhar V, Mundkar S, Munim F. Primary Amoebic Meningoencephalitis in an Infant due to Naegleria fowleri. Case Rep Neurol Med. 2011. 2011:782539. [Medline].

  15. Shakoor S, Beg MA, Mahmood SF, Bandea R, Sriram R, Noman F. Primary amebic meningoencephalitis caused by Naegleria fowleri, Karachi, Pakistan. Emerg Infect Dis. 2011 Feb. 17(2):258-61. [Medline].

  16. Herriman R. Sindh Naegleria fowleri death toll reaches a dozen in 2015. Outbreak News Today. 2015.

  17. Phu NH, Hoang Mai NT, Nghia HD, Chau TT, Loc PP, Thai le H. Fatal consequences of freshwater pearl diving. Lancet. 2013 Jan 12. 381(9861):176. [Medline].

  18. Ithoi I, Ahmad AF, Nissapatorn V, Lau YL, Mahmud R, Mak JW. Detection of Naegleria species in environmental samples from Peninsular Malaysia. PLoS One. 2011. 6(9):e24327. [Medline].

  19. Tung MC, Hsu BM, Tao CW, Lin WC, Tsai HF, Ji DD. Identification and significance of Naegleria fowleri isolated from the hot spring which related to the first primary amebic meningoencephalitis (PAM) patient in Taiwan. Int J Parasitol. 2013 May 9. [Medline].

  20. Ozçelik S, Coskun KA, Yunlu O, Alim A, Malatyali E. The prevalence, isolation and morphotyping of potentially pathogenic free-living amoebae from tap water and environmental water sources in Sivas. Turkiye Parazitol Derg. 2012. 36(4):198-203. [Medline].

  21. Shin HJ, Im KI. Pathogenic free-living amoebae in Korea. Korean J Parasitol. 2004 Sep. 42(3):93-119. [Medline].

  22. Vargas-Zepeda J, Gomez-Alcala AV, Vasquez-Morales JA, Licea-Amaya L, De Jonckheere JF, Lares-Villa F. Successful treatment of Naegleria fowleri meningoencephalitis by using intravenous amphotericin B, fluconazole and rifampicin. Arch Med Res. 2005 Jan-Feb. 36(1):83-6. [Medline].

  23. Rai R, Singh DK, Srivastava AK, Bhargava A. Primary amebic meningoencephalitis. Indian Pediatr. 2008 Dec. 45(12):1004-5. [Medline].

  24. Gautam PL, Sharma S, Puri S, Kumar R, Midha V, Bansal R. A rare case of survival from primary amebic meningoencephalitis. Indian J Crit Care Med. 2012 Jan. 16(1):34-6. [Medline].

  25. Diaz J. Seasonal primary amebic meningoencephalitis (PAM) in the south: summertime is PAM time. J La State Med Soc. 2012 May-Jun. 164(3):148-50, 152-5. [Medline].

  26. Cabanes PA, Wallet F, Pringuez E, Pernin P. Assessing the risk of primary amoebic meningoencephalitis from swimming in the presence of environmental Naegleria fowleri. Appl Environ Microbiol. 2001 Jul. 67(7):2927-31. [Medline].

  27. Visvesvara GS, Sriram R, Qvarnstrom Y, Bandyopadhyay K, Da Silva AJ, Pieniazek NJ, et al. Paravahlkampfia francinae n. sp. masquerading as an agent of primary amoebic meningoencephalitis. J Eukaryot Microbiol. 2009 Jul-Aug. 56 (4):357-66. [Medline].

  28. Parija SC, Dinoop K, Venugopal H. Management of granulomatous amebic encephalitis: Laboratory diagnosis and treatment. Trop Parasitol. 2015 Jan-Jun. 5 (1):23-8. [Medline].

  29. Schuster FL. Cultivation of pathogenic and opportunistic free-living amebas. Clin Microbiol Rev. 2002 Jul. 15 (3):342-54. [Medline].

  30. Reveiller FL, Cabanes PA, Marciano-Cabral F. Development of a nested PCR assay to detect the pathogenic free-living amoeba Naegleria fowleri. Parasitol Res. 2002. 88:443-50.

  31. Marciano-Cabral F, MacLean R, Mensah A, LaPat-Polasko L. Identification of Naegleria fowleri in domestic water sources by nested PCR. Appl Environ Microbiol. 2003 Oct. 69(10):5864-9. [Medline].

  32. Johnson PE, Deromedi AJ, Lebaron P, Catala P, Havens C, Pougnard C. High throughput, real-time detection of Naegleria lovaniensis in natural river water using LED-illuminated Fountain Flow Cytometry. J Appl Microbiol. 2007 Sep. 103(3):700-10. [Medline].

  33. Flores BM, Garcia CA, Stamm WE, Torian BE. Differentiation of Naegleria fowleri from Acanthamoeba species by using monoclonal antibodies and flow cytometry. J Clin Microbiol. 1990 Sep. 28(9):1999-2005. [Medline].

  34. Madarova L, Trnkova K, Feikova S, Klement C, Obernauerova M. A real-time PCR diagnostic method for detection of Naegleria fowleri. Exp Parasitol. 2010 Sep. 126(1):37-41. [Medline].

  35. Visvesvara GS. Amebic meningoencephalitides and keratitis: challenges in diagnosis and treatment. Curr Opin Infect Dis. 2010 Dec. 23(6):590-4. [Medline].

  36. 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 Oct. 44 (10):3589-95. [Medline].

  37. Kim JH, Jung SY, Lee YJ, Song KJ, Kwon D, Kim K. Effect of therapeutic chemical agents in vitro and on experimental meningoencephalitis due to Naegleria fowleri. Antimicrob Agents Chemother. 2008 Nov. 52(11):4010-6. [Medline].

  38. Investigational Drug Available Directly from CDC for the Treatment of Infections with Free-Living Amebae. MMWR Morb Mortal Wkly Rep. 2013 Aug 23. 62(33):666. [Medline].

  39. Debnath A, Tunac JB, Galindo-Gomez S, Silva-Olivares A, Shibayama M, McKerrow JH. Corifungin, a new drug lead against Naegleria, identified from a high-throughput screen. Antimicrob Agents Chemother. 2012 Nov. 56(11):5450-7. [Medline].

  40. Garcia A, Goni P, Cieloszyk J, Fernandez MT, Calvo-Beguería L, Rubio E. Identification of free-living amoebae and amoeba-associated bacteria from reservoirs and water treatment plants by molecular techniques. Environ Sci Technol. 2013 Apr 2. 47(7):3132-40. [Medline].

  41. Carrasco-Yepez M, Rojas-Hernandez S, Rodriguez-Monroy MA, Terrazas LI, Moreno-Fierros L. Protection against Naegleria fowleri infection in mice immunized with Cry1Ac plus amoebic lysates is dependent on the STAT6 Th2 response. Parasite Immunol. 2010 Sep-Oct. 32(9-10):664-70. [Medline].

  42. Kim JH, Lee SH, Sohn HJ, Lee J, Chwae YJ, Park S. The immune response induced by DNA vaccine expressing nfa1 gene against Naegleria fowleri. Parasitol Res. 2012 Dec. 111(6):2377-84. [Medline].

Hematoxin and eosin (H&E)-stained photomicrograph (125X) that shows the cytoarchitectural histopathology found in a case of primary amoebic meningoencephalitis (PAM), caused by Naegleria gruberi. Courtesy of the US Centers for Disease Control and Prevention and Dr. George R. Healy.
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