Brain Eating Amoeba: Naegleria fowleri

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What is Naegleria fowleri?

Yes, there are things that can eat your brain: the Naegleria fowleri story.

So far this summer, three people have died from the amoeba, Naegleria fowleri, now being called the "brain-eating amoeba." Naegleria fowleri is the genus and species name of an ameboflagellate. This particular amoeba causes a serious inflammation of the brain and spinal canal called primary amebic meningoencephalitis (PAM), mainly affecting children and young adults. The amoeba exists in three distinct forms, free-living cysts, trophozoites, and flagellated forms. Its life cycle is mainly in the cyst to trophozoite to cyst cycle (see image) and resembles other amoeba such as Acanthamoeba. The organism was officially discovered in Australia in 1965 by Drs. M. Fowler (hence the scientific name) and R. Carter. It probably has been occasionally infecting humans, however, for centuries.

Diagram of life cycle and rare infection pathway of humans for Naegleria fowleri
Diagram of life cycle and rare infection pathway of humans for Naegleria fowleri

How Common are Brain Eating Infections?

Fortunately, humans are rarely infected with Naegleria fowleri. Most doctors do not ever see or diagnosis this infection in any of their patients. Although the organisms can be found worldwide, mainly in warm waters (lakes, rivers, hot springs, power plant warm water discharge pools) that have loose sediment, are stagnant or contaminated with stirred up bottom sediment, or even in poorly chlorinated swimming pools, only about 121 cases have occurred in the US according to the CDC. Only one person has reportedly survived a diagnosed case of primary amebic meningoencephalitis caused by this parasite.

So how does this organism get in to "eat the brain?" The trophozoites of Naegleria first penetrate the nasal mucosa; speculation is that forceful water (for example, diving or jumping into water) contaminated with trophozoites aids this nasal penetration. The parasites then migrate to the olfactory nerves (responsible for smell) where they cause nerve cell death. Following the path of the nerve fibers, the parasites cross through the holes in the bone that allow the nerves to enter the brain. Then the trophozoites simply begin to destroy and consume all types of brain cells (in other words, trophozoites eat the brain). Some trophozoites change forms to become flagellated forms that are rarely, if ever, seen in infected individuals; cyst forms are not seen in infected people.

Medically Reviewed by a Doctor on 5/13/2016

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