Even though encounters with the microscopic bug are extraordinarily rare, it's killed six boys and young men this year. The spike in cases has health officials concerned, and they are predicting more cases in the future.
"This is definitely something we need to track," said Michael Beach, a specialist in recreational waterborne illnesses for the Centers for Disease Control and Prevention.
"This is a heat-loving amoeba. As water temperatures go up, it does better," Beach said. "In future decades, as temperatures rise, we'd expect to see more cases."
According to the CDC, the amoeba called Naegleria fowleri (nuh-GLEER-ee-uh FOWL'-erh-eye) killed 23 people in the United States, from 1995 to 2004. This year health officials noticed a spike with six cases
- three in Florida, two in Texas and one in Arizona. The CDC knows of only several hundred cases worldwide since its discovery in Australia in the 1960s.
In Arizona, David Evans said nobody knew his son, Aaron, was infected with the amoeba until after the 14-year-old died on Sept. 17. At first, the teen seemed to be suffering from nothing more than a headache.
"We didn't know," Evans said. "And here I am: I come home and I'm burying him."
After doing more tests, doctors said Aaron probably picked up the amoeba a week before while swimming in the balmy shallows of Lake Havasu, a popular man-made lake on the Colorado River between Arizona and California.
Though infections tend to be found in southern states, Naegleria lives almost everywhere in lakes, hot springs, even dirty swimming pools, grazing off algae and bacteria in the sediment.
Beach said people become infected when they wade through shallow water and stir up the bottom. If someone allows water to shoot up the nose
- say, by doing a somersault in chest-deep water - the amoeba can latch onto the olfactory nerve.
The amoeba destroys tissue as it makes its way up into the brain, where it continues the damage, "basically feeding on the brain cells," Beach said.
People who are infected tend to complain of a stiff neck, headaches and fevers. In the later stages, they'll show signs of brain damage such as hallucinations and behavioral changes, he said.
Once infected, most people have little chance of survival. Some drugs have stopped the amoeba in lab experiments, but people who have been attacked rarely survive, Beach said.
"Usually, from initial exposure it's fatal within two weeks," he said.
Researchers still have much to learn about Naegleria. They don't know why, for example, children are more likely to be infected, and boys are more often victims than girls.
"Boys tend to have more boisterous activities (in water), but we're not clear," Beach said.