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
- In individual who has had nasal passage exposure to warm water (via swimming, hot tub, nasal rinses)
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])
- Typically demonstrates elevated protein and elevated white blood cell (WBC) count with lymphocyte predominance
- CBC – usually without leukocytosis
- Lumbar puncture with CSF analysis
- 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
- Pathogenic species that infect humans
- 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
- Keratitis
- 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
- Chronic granulomatous amoebic encephalitis
- 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
- Primary amoebic meningoencephalitis
- 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
- B. mandrillaris infection
ARUP Laboratory 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
Qualitative Culture/Microscopy/Giemsa Stain
Use to rule out bacterial meningitis
Automated Cell Count/Differential
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)
Semi-Quantitative Enzyme-Linked Immunosorbent Assay/Semi-Quantitative Chemiluminescent Immunoassay
Use to rule out most common viral etiologies
Not a preferred test; refer to relevant test for the specific pathogen suspected
Semi-Quantitative Enzyme-Linked Immunosorbent Assay/Semi-Quantitative Chemiluminescent Immunoassay
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
Qualitative Calcofluor Stain/Microscopy
Detect Acanthamoeba spp and N. fowleri in various specimen types
Qualitative Culture/Microscopy
Medical Experts
Couturier

References
18636064
19660733
17975435
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.
Panel includes measles, mumps, varicella-zoster virus, herpes simplex virus (HSV) types 1 and 2, and West Nile virus antibodies