Acanthamoeba and Naegleria

Acanthamoeba and Naegleria

 

Acanthamoeba and Naegleria are the most common free-living amoeba associated with human disease.  Balamuthia mandrillaris and Hartmannella species are also free-living amoeba, but less commonly cause clinically significant infections.

  • Pathogenic species may cause fatal central nervous system (CNS) disease

Epidemiology

  • Incidence – acanthamoeba keratitis – .3-1/100,000
  • Transmission – contaminated water or soil

Organisms

  • Acanthamoeba pathogenic species that infect humans:
    • A. culbertsoni
    • A. castellanii
    • A. polyphaga
    • A. astronyxis
  • Naegleria pathogenic species that infect humans:
    • N. fowleri is the only species that infects humans
  • Balamuthia mandrillaris
  • Hartmannella species

Risk Factors

  • Acanthamoeba infection
    • Keratitis
      • Hydrogel contact lens wearers with poor hygienic practices
      • Patients exposed to contaminated water
    • Meningitis
      • Almost exclusively in patients with HIV, cirrhosis, systemic lupus erythematosus and diabetes mellitus
  • 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 amoebas

Clinical Presentation

  • Acanthamoeba
    • Chronic granulomatous amoebic encephalitis
      • Headache, stiff neck, cranial nerve involvement, fever, hemiparesis, ataxia
    • Ocular
      • Corneal ulcers, keratitis, anterior ureitis
      • Chronic granulomatous skin lesions
  • Balamuthia mandrillaris
    • Amoebic encephalitis
    • Chronic granulomatous skin lesions (papulonodular, erythematosus, possible ulceration)
    • Oral cavity lesions ( palate deformity)
  • Naegleria
    • Primary amoebic encephalitis
      • Acute onset of headache, fever, cranial nerve involvement, stiff neck, nausea, vomiting
      • Almost always fatal within 4-6 days  

Diagnosis

  • Laboratory testing
    • Acanthamoeba or Balamuthia
      • Histopathological diagnosis (brain or skin biopsy) using traditional stains, immunofluorescence, or molecular assays
      • Culture (CSF, eye)
    • Naegleria
      • CSF examination for trophozoites with Wright’s or Giemsa stain
      • Histopathologic diagnosis (brain biopsy) using traditional stains, immunofluorescence, or molecular assays
      • Culture (CSF, eye)

Differential diagnosis

  • Central nervous system disease – viral , bacterial or fungal meningitis
  • Corneal disease – herpes simplex virus, adenovirus
  • Skin disease – dimorphic fungal or mycobacterial infections

See Also