Brain Eating Amoeba: Naegleria fowleri

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.

Symptoms of brain-eating amoebas

Symptoms may start about 1 day to 1 week after exposure; initially symptoms may include:

The patient may have confusion, ataxia (wobbliness), and seizures; and rapidly worsen over about 3 to 7 days with death occurring about 7 to 14 days after exposure. Patients, who are usually young, may not seek medical care quickly; most patients are diagnosed by examination of autopsied brain tissue.

Diagnosis of brain-eating amoebas

Diagnosis may be done by examination of CSF fluid by microscopic visualization and by specialized culture techniques. However, most patients that are alive when they were diagnosed have such advanced disease that survival is rare, even with extensive treatment and supportive measures.

The CDC suggests that Amphotericin B is the drug of choice to treat primary amebic meningoencephalitis but there is no data suggesting this is effective. Chlorpromazine may also be useful. Earlier diagnosis may help future Naegleria-infected patients. Researchers are developing rapid PCR tests but none are currently available.

Brain-eating amoeba prevention

Prevention seems the best way to avoid this rare "brain eating" disease. Abstaining from all water-related activities can prevent Naegleria infections, but for many people, this simply is not an option. There are other things people can do.

  • Avoid swimming in still, warm, brackish water that has loose bottom sediment.
  • Avoid jumping or diving into the same type of water.
  • Wear a nose clip or hold your nose if you jump or dive into relatively warm water lakes, rivers, pools or other similar bodies of water.

The highest incidence of this disease occurs in the hot summer months in children and young adults, with males having the highest incidence of disease. Be careful out there!


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Medically reviewed by Robert Cox, MD; American Board of Internal Medicine with subspecialty in Infectious Disease

REFERENCES: Parasites - Naegleria. Primary Amebic Meningoencephalitis --- Arizona, Florida, and Texas, 2007. Naegleria Infection.