The Center for Disease Control (CDC) reported on Friday that a rare water-borne amoeba, that swims up through the nose and infects the brain, has claimed the lives of three young Americans.
Naegleria fowleri -- an amoeba found in warm freshwater lakes and rivers and occasionally in poorly treated swimming pools -- causes a "rare, but severe" brain infection and kills around three people a year, the CDC said.
In the first week the disease causes major headaches, fever, vomiting and a stiffening of the neck, eventually leading to confusion, seizures and hallucinations. The disease is almost always fatal.
There is no apparent cure for the extremely rare disease, though some drugs have proved effective in the laboratory, the CDC said.
Just 32 people were infected in the United States from 2001 to 2010, far less than the 36,000 drowning deaths recorded between 1996 and 2005, according to the CDC.
The center provides more information at www.cdc.gov/parasites/naegleria.
Earlier this month a 16-year-old died of the infection after an outdoor swim in Florida and a nine-year-old died in Virginia after contracting the disease at a summer fishing camp.
In June a 20-year-old in Louisiana was infected by a contaminated nasal allergy spray. The disease is more common in the balmy US southern states.
Amoebas thrive in warm water, and another species, Entamoeba histolytica, causes intestinal disease, particularly in tropical climates with poor sanitary conditions.