Acanthamoeba and Naegleria - Primary Amebic Meningoencephalitis (Brain-Eating Amoeba) and Acanthamoeba Keratitis

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.

Diagnosis

Indications for Testing

  • Acanthamoeba
    • Eye pain, redness, sensitivity to light, change in vision, sensation of foreign body in eye, and/or excessive tearing, particularly in contact lens wearer who has had ocular exposure to warm water at risk for contamination with Acanthamoeba parasite
    • Consider acanthamoebic keratitis after ruling out other causes of acute keratitis
  • Naegleria
    • In individual who has had nasal passage exposure to warm water (via swimming, hot tub, nasal rinses)
      • Severe headache, fever, nausea, and vomiting symptoms that progress to stiff neck, seizures, confusion, hallucinations, and coma (CDC)
      • Absence of routine organisms in cerebrospinal fluid (CSF)
      • Lack of response to conventional antibiotics

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 white blood cell (WBC) count with lymphocyte predominance
        • Elevated red blood cells (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 herpes simplex virus [HSV])
    • CBC – usually without leukocytosis
  • Initial testing for keratitis – culture of eye specimen

Histology

  • Acanthamoeba – biopsy and pathologist examination of involved sites useful for diagnosis of disseminated disease
  • Naegleria – biopsy and pathologist examination can be useful for diagnosis
  • Useful stains include calcofluor stain and Giemsa stain

Differential Diagnosis

Background

Epidemiology

  • Incidence
    • Acanthamoeba keratitis – 0.3-1/100,000
    • Naegleria, Balamuthia, Sappinia – 4/million
  • 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 that is highly resistant to antimicrobial agents
  • Naegleria pathogenic species – N. fowleri is the only species known to infect humans
  • Other pathogenic free-living amoebae include Balamuthia mandrillaris and Sappinia pedata

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
    • 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
    • N. fowleri and B. mandrillaris can also infect immunocompetent patients

Clinical Presentation

  • Acanthamoeba infection
    • Chronic granulomatous amoebic encephalitis
      • Fever, nausea, headache, vomiting, stiff neck, cranial nerve involvement, hemiparesis, ataxia
      • Fatality ratio of >90%
    • Ocular disorders and symptoms
      • Corneal ulcers, punctuate keratitis, anterior uveitis
      • Complications
        • Secondary glaucoma
        • Cataract
        • Iris atrophy
    • Chronic granulomatous skin lesions
  • N. fowleri infection
    • Primary amoebic meningoencephalitis
      • Acute onset of fever, nausea, vomiting, headache, stiff neck, cranial nerve involvement
      • Almost always fatal within 4-6 days
  • Other pathogenic free-living amoebae-caused infections
    • B. mandrillaris infection
      • Amoebic encephalitis
      • Chronic granulomatous skin lesions – papulonodular, erythematosus, possible ulceration
      • Oral cavity lesions – palate deformity
    • S. pedata infection
      • Amoebic encephalitis

ARUP Lab Tests

Primary Tests

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

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

Culture does not detect Balamuthia mandrillaris – detected only by stain

Use to rule out bacterial meningitis

Use to rule out most common viral etiologies

Molecular testing is preferred for patients presenting with meningitis/encephalitis; refer to meningitis/encephalitis panel by polymerase chain reaction (PCR)

Panel includes measles, mumps, varicella-zoster virus, herpes simplex virus (HSV) types 1 and 2, and West Nile virus antibodies

Related Tests

Use to rule out most common viral etiologies

Not a preferred test; refer to relevant test for the specific pathogen suspected

Panel includes measles, mumps, varicella-zoster virus, herpes simplex virus (HSV) types 1 and 2, and West Nile antibodies

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

Detect Acanthamoeba spp and N. fowleri in various specimen types

Medical Experts

Contributor

Couturier

Marc Roger Couturier, PhD, D(ABMM)
Associate Professor of Clinical Pathology, University of Utah
Medical Director, Parasitology/Fecal Testing, Infectious Disease Antigen Testing, Bacteriology, and Molecular Amplified Detection, ARUP Laboratories

References

Additional Resources