Brain-Eating Ameba

Primary Amebic Meningoencephalitis

Jennifer Cope, MD

May 28, 2013

Editorial Collaboration

Medscape &

This feature requires the newest version of Flash. You can download it here.
In This Article

Primary Amebic Meningoencephalitis

Hello. I'm Dr. Jennifer Cope, an epidemiologist with the Waterborne Disease Prevention Branch at CDC. I am here today as part of the CDC Expert Commentary Series on Medscape.

I would like to speak with you about a disease called primary amebic meningoencephalitis (PAM). It is a rare and devastating infection of the brain caused by the free-living ameba Naegleria fowleri which has been called the "brain-eating ameba" in the media. First I will give you some brief information on when and where infection often occurs. Then I will discuss the diagnosis and treatment of PAM. Finally, I will tell you about the prevention messages you can share with your patients.

Naegleria fowleri is commonly found in warm freshwater, such as lakes, rivers, streams, and hot springs. The ameba infects people when contaminated water enters the body through the nose. It then travels up the olfactory nerve to the brain where it causes PAM, which is usually fatal. Infection typically occurs when people go swimming or diving in warm freshwater. In very rare instances, PAM may also occur when contaminated water from other sources, such as inadequately chlorinated swimming pool water or contaminated tap water, enters the nose.

In the United States there have been 128 PAM cases from 1962 through 2012, with only 1 survivor.[1] Most infections occurred in southern-tier states, with more than half in Texas and Florida. PAM also disproportionately affects males and children, maybe because of the types of water activities (such as diving or watersports) that might be more common among young boys. Recently, cases of PAM have been identified in states as far north as Minnesota, possibly due to rising average water temperatures.[1,2]

Although swimming in warm freshwater remains the predominant risk factor for infection, in 2011, 2 cases of PAM in Louisiana, in people who did not have a recent history of swimming in warm freshwater, were found to be regular users of neti pots for sinus irrigation and apparently made their irrigation solutions with Naegleria fowleri-contaminated household tap water.[3] (Figure 1).

Figure 1. In very rare instances, Naegleria infections may occur when contaminated water enters the nose, for example when people irrigate their sinuses (via the nose) using a neti pot.

In other countries, PAM has occurred in patients who perform ritual nasal rinsing, which is practiced to prepare for prayer in some religions.[4]