Amoebas are single-celled organisms. The so-called brain-eating amoeba is a species discovered in 1965. Its formal name is Naegleria fowleri. It usually lurks in warm freshwater bodies or untreated, contaminated waters. When it finds its way inside the human body, it causes a rare, yet deadly infection and inflammation in the brain and eventually destroys the brain tissue by “eating” it. Doctors call this disease primary amebic meningoencephalitis (PAM). You can only get it when contaminated water with the brain-eating amoeba travels up your nose.
What Is a Brain-Eating Amoeba?
There are several species of Naegleria but only the fowleri species causes PAM. It was first identified in Australia, but this amoeba is believed to have evolved here in the U.S.
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 115 F.
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
- Splash pads for children
- Water parks
Naegleria can’t live in saltwater. It can’t survive in properly treated swimming pools or in properly treated municipal water. You also can’t get infected by drinking contaminated water.
Most cases of N. fowleri disease occur in Southern or Southwestern states. Over half of all infections have been in Florida and Texas.
What Are the First Symptoms Someone Might Have?
Symptoms of PAM are not specific to this disease. At first, PAM may seem like viral meningitis. Symptoms include:
- headache
- fever
- stiff neck
- loss of appetite
- vomiting
- altered mental state
- seizures
- coma
There may also be hallucinations, drooping eyelid, blurred vision, and loss of the sense of taste.
How Long Until Symptoms of a Brain-Eating Amoeba Appear?
It takes two to 15 days for symptoms to appear after N. fowleri amoebas enter the nose. Death usually occurs 3 to 7 days after symptoms appear. The average time to death is 5.3 days from symptom onset. Only a handful of patients worldwide have been reported to have survived an infection.
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.
How Frequently Do People Get Infected by a Brain-Eating Amoeba?
Even though N. fowleri amoebas are relatively common, they only rarely cause brain disease. N. fowleri disease is known as primary amoebic meningoencephalitis (PAM). It occurs from zero to eight times a year, almost always from July to September.
It’s considered a rare infection. But some cases may be unreported. A study in Virginia that looked at more than 16,000 autopsy records from patients who died of meningitis found five previously unreported cases of PAM.
Studies show that many people may have antibodies to N. fowleri. That suggests that they became infected with the amoeba but that their immune systems fought it off.
It’s not at all clear whether N. fowleri is a rare infection that always causes PAM and is almost always fatal, or a more common infection that only sometimes causes PAM.
In a 2009 study, CDC researchers suggested that the common finding of antibodies to the amoeba in humans and the frequent finding of N. fowleri in U.S. waters indicates “that exposure to the amoeba is much more common than the incidence of PAM suggests.”