Naegleria fowleri Infection (Brain-Eating Amoeba Infection)

  • Medical Author:

    Sandra Gonzalez Gompf, MD, FACP is a U.S. board-certified Infectious Disease subspecialist. Dr. Gompf received a Bachelor of Science from the University of Miami, and a Medical Degree from the University of South Florida. Dr. Gompf completed residency training in Internal Medicine at the University of South Florida followed by subspecialty fellowship training there in Infectious Diseases under the directorship of Dr. John T. Sinnott, IV.

  • 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.

What is Naegleria fowleri?

Naegleria fowleri is an amoeba in the phylum of protozoa called Percolozoa. It normally lives in freshwater and soil, consuming organic matter and bacteria. The organism goes through three stages in its life cycle: cyst, flagellate, and trophozoite. Cysts are highly stable in the environment and can withstand near-freezing temperatures. The flagellate form is an intermediate stage that moves about but does not consume nutrients or reproduce. The trophozoite form is the active, eating, reproducing phase. Animals and humans are "accidental hosts." PAM occurs only when an animal or human enters the environment at a time when amoebae are actively reproducing and seeking food. Naegleria are "thermophilic," meaning that they become active in warmer water. They live in both tropical and temperate climates throughout the world. The organism is commonly found in any freshwater, including rivers, lakes, drainage ditches, ponds, or any other water exposed to soil. It is also common in hot springs or in localized areas where warmer water is discharged into lakes. It has been found in poorly chlorinated swimming pools. Where the water temperature is cool, Naegleria may be found in the sediment at the bottom of lakes in its protective cyst form, where it survives winters. The most infectious form is the trophozoite stage, but cysts may also become infectious within a few hours of detecting favorable conditions. The flagellated stage can become trophozoite within minutes.

In recent years, Naegleria fowleri was discovered in public drinking water and plumbing in New Orleans. Naegleria is resistant to low levels of chlorine, and chlorine dissipates the further treated water travels from a treatment plant. This was discovered after three fatal cases in which the only risk factors were irrigation of sinuses with tap water and playing on a hose-fed Slip 'N Slide. Naegleria was found in the hose, in drinking water, and hot water heaters in these cases. Australia has known of Naegleria in drinking water for 30 years, when the first cases of PAM were described related to public drinking water. Since then, Australia has maintained a water treatment system that eliminates it. Louisiana implemented the Australian model in 2013, which includes regular monitoring for Naegleria and chlorine, and increasing chlorine for 60 days if the amoeba is found. (This is called a "chlorine burn.")

Naegleria fowleri cannot live in saltwater and is not found in the ocean.

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

Medically Reviewed by a Doctor on 8/18/2016

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