Acanthamoeba/Naegleria species, Corneal Scraping or Spinal Fluid
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
The free-living amebae are ubiquitous in the environment, and may be found in soil and fresh water sources. Naegleria fowleri may enter the central nervous system (CNS) during exposure to infected water and cause a fulminant meningitis in previously healthy individuals. In contrast, Acanthamoeba species and Balamuthis mandrillaris cause chronic granulomatous encephalitis in immunocompromised (and, rarely, immunocompetent) adults, and typically disseminate to the CNS from a primary lung or skin source.
Acanthamoeba species can also cause a painful keratitis when organisms are introduced into the eye. This typically occurs during contact lens use when the lenses or storage or cleaning solutions are contaminated. Amebae can also enter the cornea with abrasion or trauma. Amebic keratitis can cause blindness if untreated. Most cases respond to treatment once a diagnosis is made, but some cases prove to be resistant to therapy with no antimicrobials uniformly active against the organisms.
Diagnosis of Acanthamoeba species and Naegleria fowleri, in central nervous system or ocular specimens
Organisms seen on stains of the original specimen smear or growth on culture media are positive tests.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
The preferred specimens for Acanthamoeba ocular culture are corneal scrapings or biopsy. Swabs are suboptimal and may result in a falsely negative result. Submission of slides without material for culture is not acceptable.
Wooden-handled swabs are unacceptable for culture since the wood may contain preservatives or other chemicals inhibitory to Acanthamoeba or Naegleria growth.
Transport media that contains antibiotics is not acceptable for this testing (M4 or M5 media or any other viral transport media). Thioglycollate broth is also unacceptable.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Negative for Acanthamoeba species
CENTRAL NERVOUS SYSTEM
Negative for Acanthamoeba/Naegleria species
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Acanthamoeba keratitis multiple states, 2005-2007. MMWR Morb Mortal Wkly Rep 2007;56(21):532-534
2. Kumar R, Lloyd D: Recent advances in the treatment of Acanthamoeba keratitis. Clin Infect Dis 2002 Aug 15;35(4):434-441
3. Yoder JS, Eddy BA, Visvesvara GS, et al: The epidemiology of primary amoebic meningoencephalitis in the USA, 1962-2008. Epidemiol Infect 2009 Oct;22:1-8
4. Schuster FL: Cultivation of pathogenic and opportunistic free-living amebas. Clin Microbiol Rev 2002 Jul;15(3):342-354