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Epidemiology of free-living ameba infections
G S Visvesvara1, J K Stehr-Green
1Division of Parasitic Diseases, Centers for Disease Control, U.S. Department of Health and Human Services, Atlanta, Georgia 30333.
Abstract:
Small free-living amebas belonging to the genera Acanthamoeba and Naegleria occur world-wide. They have been isolated from a variety of habitats including fresh water, thermal discharges of power plants, soil, sewage and also from the nose and throats of patients with respiratory illness as well as healthy persons. Although the true incidence of human infections with these amebas is not known, it is believed that as many as 200 cases of central nervous system infections due to these amebas have occurred worldwide. A majority (144) of these cases have been due to Naegleria fowleri which causes an acute, fulminating disease, primary amebic meningoencephalitis. The remaining 56 cases have been reported as due either to Acanthamoeba or some other free-living ameba which causes a subacute and/or chronic infection called granulomatous amebic encephalitis (GAE). Acanthamoeba, in addition to causing GAE, also causes nonfatal, but nevertheless painful, vision-threatening infections of the human cornea, Acanthamoeba keratitis. Infections due to Acanthamoeba have also been reported in a variety of animals. These observations, together with the fact that Acanthamoeba spp., Naegleria fowleri, and Hartmannella sp. can harbor pathogenic microorganisms such as Legionella and or mycobacteria indicate the public health importance of these amebas.
Insights
Free-living amebas like Acanthamoeba and Naegleria are found globally in diverse environments. Some species cause serious human infections, including primary amebic meningoencephalitis and Acanthamoeba keratitis, highlighting their public health significance.
Area of Science:
- Microbiology
- Environmental Health
- Parasitology
Background:
- Free-living amebas, including Acanthamoeba and Naegleria, are ubiquitous worldwide.
- These amebas inhabit various environments such as freshwater, soil, and sewage.
- They have been found in human respiratory tracts, both in healthy individuals and those with illness.
Purpose of the Study:
- To summarize the occurrence and public health implications of free-living amebas.
- To detail the types of infections caused by Acanthamoeba and Naegleria.
- To highlight the potential for these amebas to harbor other pathogens.
Main Methods:
- Literature review and case reporting analysis.
- Identification of amebic genera and associated diseases.
- Assessment of amebic habitats and potential pathogen co-habitation.
Main Results:
- Approximately 200 worldwide cases of amebic central nervous system infections reported.
- Naegleria fowleri causes primary amebic meningoencephalitis (144 cases).
- Acanthamoeba causes granulomatous amebic encephalitis (56 cases) and Acanthamoeba keratitis.
Conclusions:
- Free-living amebas pose significant public health risks due to severe human infections.
- Acanthamoeba keratitis is a painful, vision-threatening corneal infection.
- The ability of these amebas to harbor pathogens like Legionella underscores their importance.