phoenix -- It sounds like science fiction, but it's true: Killer amoebas living in lakes can enter the body through the nose and attack the brain, where they feed until you die.
Though encounters with the microscopic bug are extraordinarily rare, it is known to have killed six boys and young men in the United States this year; over the decade ending in 2004, the yearly average was 2.3.
The jump in cases has health officials concerned.
"This is definitely something we need to track," said Michael Beach, a specialist in recreational waterborne illnesses with the Centers for Disease Control and Prevention. "This is a heat-loving amoeba. As water temperatures go up, it does better. In future decades, as temperatures rise, we'd expect to see more cases."
The amoeba, called Naegleria fowleri, killed 23 people in the U.S. from 1995 to 2004, the CDC says. The CDC knows of only several hundred cases worldwide since the microbe's discovery in Australia in the 1960s.
This year, there have been three cases in Florida, two in Texas and one in Arizona.
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.
A person wading through shallow water stirs up the bottom, and if water gets up the person's nose, the amoeba can latch onto the olfactory nerve, which is responsible for conveying smells to the brain.
The amoeba makes its way to the brain, destroying tissue as it goes, Beach said.
The easiest way to prevent infection, Beach said, is to use nose clips when swimming or diving in fresh water.
People who are infected tend to complain of a stiff neck, headaches and fevers. In the later stages, they show signs of brain damage, such as hallucinations and behavioral changes, he said.
Some drugs have stopped the amoeba in lab experiments, but people who have been infected rarely survive, Beach said. "Usually, from initial exposure it's fatal within two weeks," he said.
In central Florida, authorities started an amoeba phone hotline advising people to avoid warm standing water and areas with algae blooms. Texas officials also have issued warnings.
Officials in Lake Havasu City in Arizona, where one boy may have become infected, are discussing whether to take action. "Some folks think we should be putting up signs," city spokesman Charlie Cassens said. "Some people think we should close the lake."
Beach cautioned that people shouldn't panic about the dangers of the brain-eating bug. Cases are still extremely rare.