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."
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 three to seven 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.
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:
- stiff neck
- loss of appetite
- altered mental state
There may also be hallucinations, drooping eyelid, blurred vision, and loss of the sense of taste.
Is There a Treatment for Infection With Brain-Eating Amoeba?
The right treatment isn't clear. A number of drugs kill N. fowleri amoebas in the test tube. But even when treated with these drugs, very few patients survive.
Is There a Rapid Test for Infection With Brain-Eating Amoeba?
There is no rapid test for infection with brain-eating amoeba. But researchers are working to develop one. Until such tests come along, it can take weeks to identify the amoeba.
How Do Amoebas Dissolve Brain Tissue?
One study suggests that N. fowleri amoebas produce two proteases -- enzymes that dissolve protein.
Are Certain Groups Affected More Than Others?
Over 60% of U.S. cases are in children age 13 or younger. About 80% of cases are in males.
It's not at all clear whether children or males are more susceptible to the amoeba, or whether young males are more likely to engage in activities that expose them to the amoeba.