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.

Tabs Content

Clinical Overview

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

Central nervous system (CNS) disease
- Viral encephalitis
- Bacterial leptomeningitis
- Fungal meningitis
- Mycobacterium tuberculosis meningitis
Corneal disease
- HSV
- Atypical mycobacteria
- Adenovirus
- Varicella-zoster virus
- Ophthalmic manifestations of autoimmune disease
- Ophthalmic rosacea
Skin disease
- Dimorphic fungal infections
- Mycobacterial infections

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

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 Stain, CSF 3000878
Method: Qualitative Culture/Microscopy/Giemsa Stain

Recommended Use

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

Limitations

Culture does not detect Balamuthia mandrillaris – detected only by stain

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

Recommended Use

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

Recommended Use

Use to rule out most common viral etiologies

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

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

Medical Experts

Couturier, Marc Roger, PhD, D(ABMM), Medical Director, Microbial Immunology, Parasitology and Fecal Testing, and Infectious Disease Antigen Testing at ARUP Laboratories; Associate Professor of Clinical Pathology, University of Utah

References

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

Last Update: June 2019

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

Diagnosis

Indications for Testing

Laboratory Testing

Histology

Differential Diagnosis

Background

Epidemiology

Organisms

Risk Factors

Clinical Presentation

ARUP Lab Tests

Medical Experts

References

General References

ARUP Laboratories

ARUP Websites

ARUP Consult


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

Diagnosis

Indications for Testing

Laboratory Testing

Histology

Differential Diagnosis

Background

​Epidemiology

Organisms

Risk Factors

Clinical Presentation

ARUP Lab Tests

Medical Experts

References

General References

ARUP Laboratories

ARUP Websites

ARUP Consult

Epidemiology