Acanthamoeba and Naegleria

Diagnosis

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

Histology

  • 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

Clinical Background

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.

Epidemiology

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

Organisms

  • 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

Indications for Laboratory Testing

  • 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
Test Name and Number Recommended Use Limitations Follow Up
Acanthamoeba and Naegleria Culture and Stains, CSF 2002584
Method: Qualitative Culture/Microscopy/Calcofluor Stain/Giemsa Stain

Detect Acanthamoeba spp, Naegleria spp, and other free-living amoebae

CSF specimens examined by calcofluor white and Giemsa stains upon receipt in addition to setup for culture

Culture does not detect Balamuthia mandrillaris, detected by stain

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

Use to rule out bacterial meningitis

   
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

Use to rule out most common viral etiologies

Panel includes measles, mumps, VZV, HSV-1 and HSV-2, and West Nile virus antibodies

   
Additional Tests Available
 
Click the plus sign to expand the table of additional tests.
Test Name and NumberComments
Encephalitis Panel with Reflex to Herpes Simplex Virus Types 1 and 2 Glycoprotein G-Specific Antibodies, IgG, Serum 2008915
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay/Semi-Quantitative Chemiluminescent Immunoassay

Use to rule out most common viral etiologies

Panel includes measles, mumps, varicella-zoster virus, HSV type 1 and 2, and West Nile antibodies

Amoeba Calcofluor Stain 0060250
Method: Qualitative Calcofluor Stain/Microscopy

Detect Acanthamoeba spp, Naegleria fowleri and other free-living amoebae

Acanthamoeba and Naegleria Culture 0060245
Method: Qualitative Culture/Microscopy

Diagnose Acanthamoeba spp, Naegleria spp and other free-living amoebae in CSF, corneal scrapings or tissue, or vitreous fluid specimens

CSF specimens stained with calcofluor White and Giemsa upon receipt in addition to setup for culture