Naegleria infection is caused by a parasitic amoeba found in freshwater lakes, ponds, rivers and hot springs. Only the Naegleria fowleri species infects humans, and does so by entering the body through the nose, where the amoeba then causes an infection called primary amebic meningoencephalitis (PAM).
The symptoms of PAM begin anywhere from one day to one week after the amoeba gets into your body, and often resemble the symptoms of a bacterial meningitis infection: headache, fever, nausea, vomiting and a stiff neck.
Contracting PAM is very rare in the United States. Only 32 cases were reported in the U.S. between 2001 and 2010 [source: CDC]. Unfortunately, surviving the infection is also rare. It's estimated that out of about 200 reported cases worldwide, no more than 12 or so patients have survived [source: Parija]. Once symptoms begin, the infection moves quickly, causing additional problems including seizures, confusion and hallucinations, and patients with the infection often die in less than two weeks (and sometimes less than one week).
You can minimize your risk of being infected with Naegleria fowleri by avoiding swimming or taking part in any activities where you'll be in warm, untreated or inadequately treated freshwater.