Naegleria fowleri Infection (Brain-Eating Amoeba Infection)

  • Medical Author:
    Mary D. Nettleman, MD, MS, MACP

    Mary D. Nettleman, MD, MS, MACP is the Chair of the Department of Medicine at Michigan State University. She is a graduate of Vanderbilt Medical School, and completed her residency in Internal Medicine and a fellowship in Infectious Diseases at Indiana University.

  • Medical Author: Jeremy Cauwels, MD, FACP
  • Medical Editor: Charles Patrick Davis, MD, PhD
    Charles Patrick Davis, MD, PhD

    Charles Patrick Davis, MD, PhD

    Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

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What is Naegleria fowleri?

Naegleria fowleri is an amoeba that lives in freshwater and soil. The organism goes through three stages in its life cycle: cysts, flagellates, and trophozoites. Cysts are highly stable in the environment and can withstand near-freezing temperatures. The flagellate form is an intermediate stage that does not consume nutrients or reproduce. The trophozoite form causes human disease. Naegleria are "thermophilic," meaning that they prefer warmer water. Thus, Naegleria infection is found both in tropical and temperate climates. The organism is commonly identified in freshwater, including rivers, lakes, and ponds, or in soil near these sources. Where the water temperature is cool, Naegleria may be found in the sediment at the bottom of lakes or in localized areas where warmer water is discharged into lakes. Naegleria fowleri does not exist in saltwater and is not found in the ocean.

Although there are many species of Naegleria, only Naegleria fowleri causes human infection. There are other free-living amoebas that cause human disease, including Acanthamoeba.

What causes a Naegleria fowleri infection?

N. fowleri infection is a water-borne disease. Exposure occurs when people come into contact with warm freshwater usually through swimming, diving, water skiing, or other recreational activity. Although contact with infected water is common in the United States, symptomatic disease caused by N. fowleri is rare.

The danger of serious infection comes when water containing Naegleria fowleri is forced into the nose. The amoeba then migrates through the olfactory nerves and enters the brain. The initial exposure can occur when diving or inadvertently aspirating water during swimming. Rarely, underchlorinated swimming pools have been implicated in transmission. Because Naegleria fowleri can be present in untreated well water, there is a small but real chance of transmission to young children during bathing. Naegleria fowleri has also caused disease in adults who inject water into the nose as part of ritual ablutions related to religious practices or as an irrigating solution for sinus passages.

Medically Reviewed by a Doctor on 4/8/2015

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