Naegleria fowleri (commonly referred to as the “brain-eating amoeba” or “brain-eating ameba”), is a free-living microscopic ameba*, (single-celled living organism). It can cause a rare** and devastating infection of the brain called primary amebic meningoencephalitis (PAM). The ameba is commonly found in warm freshwater (e.g. lakes, rivers, and hot springs) and soil. Naegleria fowleri usually infects people when contaminated water enters the body through the nose. Once the ameba enters the nose, it travels to the brain where it causes PAM, which is usually fatal. Infection typically occurs when people go swimming or diving in warm freshwater places, like lakes and rivers. In very rare instances, Naegleria infections may also occur when contaminated water from other sources (such as inadequately chlorinated swimming pool water or heated and contaminated tap water) enters the nose 1-4. You cannot get infected from swallowing water contaminated with Naegleria.
Top image (from left to right): Computer-generated representation of Naegleria fowleri in its ameboid trophozoite stage, in its flagellated stage, and in its cyst stage.
- Yoder JS, Eddy BA, Visvesvara GS, Capewell L, Beach MJ. The epidemiology of primary amoebic meningoencephalitis in the USA, 1962-2008. Epidemiol Infect. 2010;138(7):968-75.
- Visvesvara GS. Free-living amebae as opportunistic agents of human disease. J Neuroparasitol. 2010;1.
- Marciano-Cabral F, Cabral G. The immune response to Naegleria fowleri amebae and pathogenesis of infection. FEMS Immunol Med Microbiol. 2007;51:243-59.
- CDC. Primary amebic meningoencephalitis associated with ritual nasal rinsing — St. Thomas, U.S. Virgin Islands, 2012. MMWR Morb Mortal Wkly Rep. 2013;62(45):903.
*About the Term “Ameba”
In U.S. English, the single-celled living organism described here is an ameba. The word amoeba, with an “o”, is used as part of a scientific genus name (such as Amoeba or Acanthamoeba). In British English, both the generic organism term and genera names are spelled amoeba with an “o”.
There is no universal definition of a “rare disease” but the U.S. Rare Disease Act of 2002 defined a rare disease as affecting less than 200,000 people in the U.S. and this definition has been adopted by the National Institutes of Health, Genetic and Rare Diseases Information Centers.
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- Page last reviewed: February 28, 2017
- Page last updated: February 28, 2017
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