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Brain & Nervous System Health Center

Brain-Eating Amoeba FAQ

Rare, Fatal Amoeba Infection: Your Questions Answered
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WebMD Health News
Reviewed by Laura J. Martin, MD

Aug. 18, 2011 -- Brain-eating amoebas have killed three young Americans this summer.

What is this scary bug? How does it get to the brain? Where is it, and how can you avoid it? WebMD answers these and other questions.

What Is a Brain-Eating Amoeba?

Amoebas are single-celled organisms. The so-called brain-eating amoeba is a species discovered in 1965 and formally named Naegleria fowleri. Although first identified in Australia, this amoeba is believed to have evolved in the United States.

There are several species of naegleria, but only the N. fowleri species causes human disease. 

Like other amoebas, naegleria reproduce by cell division. When conditions are less than optimal, amoebas become inactive cysts. When conditions are favorable, the cysts turn into trophozoites -- their feeding form. These trophozoites can also temporarily grow tails that allow them to swim. In this tailed form they cannot eat, so they soon revert to the trophozoite stage.

Where Are Brain-Eating Amoebas Found?

Naegleria love warm temperatures and are able to survive in water as hot as 113 degrees Fahrenheit.

These amoebas can be found in warm places around the globe. They are found in:

  • Warm lakes, ponds, and rock pits
  • Mud puddles
  • Warm, slow-flowing rivers, especially those with low water levels
  • Untreated swimming pools and spas
  • Untreated well water or untreated municipal water
  • Hot springs and other geothermal water sources
  • Thermally polluted water, such as runoff from power plants
  • Aquariums
  • Soil, including indoor dust

Naegleria can't live in salt water and cannot survive in properly treated swimming pools or in treated municipal water.

Most cases of N. fowleri disease occur in Southern or Southwestern states. Over half of all infections have been in Florida and Texas. However, a recent case in Minnesota suggests either that the amoebas are more common in Northern states than previously known, or that they are spreading into these states.

How Do Amoebas Get in the Brain?

The moniker "brain-eating amoeba" makes naegleria sound like tiny zombies wandering about looking for a way into your skull. But brains are accidental food for them, says Jonathan Yoder, MPH, who tracks the deadly amoeba for the CDC.

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