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 diseaseNaegleria – biopsy and pathologist examination can be useful for diagnosisUseful stains include calcofluor stain and Giemsa stain
Differential Diagnosis
Central nervous system (CNS) disease
Corneal disease
Skin disease
Dimorphic fungal infections
Mycobacterial infections
Background
EpidemiologyIncidence
Acanthamoeba keratitis – 0.3-1/100,000Naegleria , 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 humansOther 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
ARUP Lab 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)
Use to rule out most common viral etiologies
Not a preferred test; refer to relevant test for the specific pathogen suspected
Detect Acanthamoeba spp, Naegleria fowleri, and other free-living amoebae
Detect Acanthamoeba spp and N. fowleri in various specimen types
Related Topics Last Update: October 2019
