The brain and spinal cord are surrounded by a clear fluid called cerebrospinal fluid (CSF). This fluid is produced and stored in cavities in the brain called ventricles. It circulates around the brain, moving from ventricle to ventricle. The purposes of the fluid are to cushion and protect the brain and spinal cord, to supply them with nutrients, and to remove some of their waste products. Any excess fluid drains away from the brain and is absorbed by veins at the top of the brain.
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
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
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.