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Brain-Eating Amoeba

It doesn't happen often. But most summers, several Americans -- usually healthy, young people -- suffer sudden, tragic deaths from a brain-eating amoeba.

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

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What Is a Brain-Eating Amoeba?

Amoebas are single-celled organisms. The so-called brain-eating amoeba is a species discovered in 1965. It's formal name is Naegleria fowleri. Although first identified in Australia, this amoeba is believed to have evolved in the U.S.

There are several species of Naegleria but only the fowleri species causes human disease. There are several fowleri subtypes. All are believed equally dangerous.

N. fowleri is microscopic: 8 micrometers to 15 micrometers in size, depending on its life stage and environment. By comparison, a hair is 40 to 50 micrometers wide.

Like other amoebas, Naegleria reproduces by cell division. When conditions aren't right, the amoebas become inactive cysts. When conditions are favorable, the cysts turn into trophozoites -- the feeding form of the amoeba.

 

Where Are Brain-Eating Amoebas Found?

Naegleria loves very warm water. It can survive in water as hot as 113 degrees Fahrenheit.

These amoebas can be found in warm places around the globe. N. fowleri is 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. It can't survive in properly treated swimming pools or in properly 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.

How Do People Get Infected With Brain-Eating Amoeba?

The term "brain-eating amoeba" makes the amoeba sound like a tiny zombie stalking your skull. But brains are accidental food for them.

According to the CDC, N. fowleri normally eats bacteria. But when the amoeba gets into humans, it uses the brain as a food source.

The nose is the pathway of the amoeba, so infection occurs most often from diving, water skiing, or performing water sports in which water is forced into the nose. But infections have occurred in people who dunked their heads in hot springs or who cleaned their nostrils with neti pots filled with untreated tap water.

A person infected with N. fowleri cannot spread the infection to another person.

How Do Amoebas Get in the Brain?

Studies suggest that N. fowleri amoebas are attracted to the chemicals that nerve cells use to communicate with one another. Once in the nose, the amoebas travel through the olfactory nerve (the nerve connected with sense of smell) into the frontal lobe of the brain.

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