Acanthamoeba and Naegleria

  • Diagnosis
  • Background
  • Lab Tests
  • References
  • Related Topics

Indications for Testing

  • Patients with symptoms of meningitis/encephalitis where cerebrospinal fluid (CSF) examination is negative for routine organisms or patient does not respond to conventional antibiotic therapy
  • Contact lens wearer with acute keratitis
    • Suspected herpetic keratitis that is not responding to therapy
    • Failure to respond to antimicrobial treatment

Laboratory Testing

  • CDC – Acanthamoeba testing recommendations
  • CDC – Naegleria testing recommendations
  • Initial testing for meningoencephalitis
    • Lumbar puncture with CSF analysis
      • Typically demonstrates elevated protein and elevated WBC count with lymphocyte predominance
        • Elevated RBCs with disease progression in primary amoebic meningoencephalitis
      • Culture
      • CSF examination for trophozoites with Wright or Giemsa stain
      • Consider viral panel testing to rule out most common viral etiologies (including HSV)
    • CBC – usually without leukocytosis
  • Initial testing for keratitis – culture of eye specimen


  • Histopathological diagnosis (brain or skin biopsy) using traditional hematoxylin and eosin, lactophenol cotton blue stain, fluorescence with calcofluor white dye, or molecular assays

Differential Diagnosis

Acanthamoeba and Naegleria are the most common free-living amoebae associated with human disease. Balamuthia mandrillaris and Hartmannella species are also free-living amoebae but less commonly cause clinically significant infections. Pathogenic species may cause fatal central nervous system (CNS) disease.


  • Incidence
    • Acanthamoeba keratitis – 0.3-1/100,000
    • Naegleria, Balamuthia, Sappinia – 4/1,000,000
  • Transmission – contaminated water or soil


  • Acanthamoeba
    • Pathogenic species that infect humans
      • A. culbertsoni
      • A. castellanii
      • A. polyphaga
      • A. astronyxis
    • The life cycle of Acanthamoeba includes both a trophozoite stage and a dormant cyst stage
      • Cysts – highly resistant to antimicrobial agents
  • Naegleria pathogenic species
    • N. fowleri – only species known to infect humans
  • Balamuthia mandrillaris
  • Sappinia pedata species

Risk Factors

  • Acanthamoeba infection
    • Keratitis
      • Soft contact lens wearers with poor hygienic practices
      • Patients exposed to contaminated water
    • Meningitis
      • Almost exclusively in immunocompromised patients
  • Naegleria infection
    • Correlates with history of swimming in lakes or brackish water
    • Aspiration of contaminated water, inhalation of contaminated dust
  • Immunosuppression is a risk factor for infection from all free-living amoebae
    • Naegleria fowleri and Balamuthia mandrillaris can also infect immunocompetent patients

Clinical Presentation

  • Acanthamoeba
    • Chronic granulomatous amoebic encephalitis
      • Fever, nausea, headache, vomiting, stiff neck, cranial nerve involvement, hemiparesis, ataxia
      • Fatality ratio of >90%
    • Ocular
      • Corneal ulcers, punctuate keratitis, anterior uveitis
      • Complications
        • Secondary glaucoma
        • Cataract
        • Iris atrophy
    • Chronic granulomatous skin lesions
  • Balamuthia mandrillaris
    • Amoebic encephalitis
    • Chronic granulomatous skin lesions – papulonodular, erythematosus, possible ulceration
    • Oral cavity lesions – palate deformity
  • Naegleria fowleri
    • Primary amoebic meningoencephalitis
      • Acute onset of fever, nausea, vomiting, headache, stiff neck, cranial nerve involvement
      • Almost always fatal within 4-6 days
  • Sappinia pedata
    • Amoebic encephalitis
Tests generally appear in the order most useful for common clinical situations. Click on number for test-specific information in the ARUP Laboratory Test Directory.

Acanthamoeba and Naegleria Culture and Stains, CSF 2002584
Method: Qualitative Culture/Microscopy/Calcofluor Stain/Giemsa Stain


Culture does not detect Balamuthia mandrillaris, detected by stain

CBC with Platelet Count and Automated Differential 0040003
Method: Automated Cell Count/Differential

Encephalitis Panel with Reflex to Herpes Simplex Virus Types 1 and 2 Glycoprotein G-Specific Antibodies, IgG, CSF 2008916
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay/Semi-Quantitative Chemiluminescent Immunoassay

General References

Centers for Disease Control and Prevention (CDC). Balamuthia amebic encephalitis--California, 1999-2007. MMWR Morb Mortal Wkly Rep. 2008; 57(28): 768-71. PubMed

Dart JK, Saw VP, Kilvington S. Acanthamoeba keratitis: diagnosis and treatment update 2009. Am J Ophthalmol. 2009; 148(4): 487-499.e2. PubMed

Foulks GN. Acanthamoeba keratitis and contact lens wear: static or increasing problem? Eye Contact Lens. 2007; 33(6 Pt 2): 412-4; discussion 424-5. PubMed

Heggie TW. Swimming with death: Naegleria fowleri infections in recreational waters. Travel Med Infect Dis. 2010; 8(4): 201-6. PubMed

Visvesvara GS. Amebic meningoencephalitides and keratitis: challenges in diagnosis and treatment. Curr Opin Infect Dis. 2010; 23(6): 590-4. PubMed

Medical Reviewers

Last Update: July 2017