PHOENIX It seemed like a headache, nothing more. But when painkillers and a trip to the emergency room didn't fix Aaron Evans, the 14-year-old asked his dad if he was going to die.
"No, no," David Evans remembers saying.
"We didn't know. And here I am: I come home and I'm burying him," the grieving father said.
What was bothering Aaron was a killer amoeba that enters the body through the nose and travels to the brain, where it feeds, destroying brain tissue.
Doctors said the teen probably picked up the microscopic amoeba, Naegleria fowleri (nuh-GLEER-ee-uh FOWL'-erh-eye), a week earlier while swimming in the balmy shallows of Lake Havasu near his home on the state's western border.
Such attacks are extremely rare, but they are usually fatal, and six boys and young men have died this year in three states. Aaron Evans' death Sept. 17 was the most recent. Some health officials have put their communities on high alert, telling people to stay away from warm, standing water.
"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, Naegleria killed 23 people in the United States from 1995 to 2004. This year health officials say they've noticed a spike in cases, with three in Florida, two in Texas and young Evans' death in Arizona. The CDC knows of only several hundred cases worldwide since its discovery in Australia in the 1960s.
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 cannonball off a cliff the amoeba can latch onto the olfactory nerve.
People who are infected tend to complain of a stiff neck, headaches and fevers, Beach said. In the later stages, they'll show signs of brain damage, such as hallucinations and behavioral changes.
There is no good treatment. Some drugs have stopped Naegleria in lab experiments, but people who have been attacked rarely survive, Beach said.
"Usually, from initial exposure it's fatal within two weeks," Beach 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.
In central Florida, authorities started an amoeba phone hot line advising people to avoid warm, standing water and areas with algae blooms. Texas health officials also have issued warnings.
People "seem to think that everything can be made safe, including any river, any creek, but that's just not the case," said Doug McBride, a spokesman for the Texas Department of State Health Services.
Officials in the town of Lake Havasu City are discussing whether to take action. "Some folks think we should be putting up signs. Some people think we should close the lake," city spokesman Charlie Cassens said.
Beach cautioned that people shouldn't panic about the dangers of the brain-eating bug. Cases are still extremely rare considering the number of people swimming in lakes.
The easiest way to prevent infection, Beach said, is to use nose clips when swimming or diving in fresh water.
"You'd have to have water going way up in your nose to begin with" to be infected, he said.
David Evans has tried to learn as much as possible about the amoeba over the past month. But it still doesn't make much sense to him. His family had gone to Lake Havasu countless times. Have people always been in danger? Did city officials know about the amoeba? Can they do anything to kill them off?
Evans lives within eyesight of the lake. Temperatures hover in the triple digits all summer, and like almost everyone else in this desert region, the Evanses look to the lake to cool off.
It was on David Evans' birthday Sept. 8 that he brought Aaron, his other two children and his parents to Lake Havasu. They ate sandwiches and spent a few hours splashing around.
"For a week, everything was fine," Evans said.
Then Aaron got the headache that wouldn't go away. At the hospital, doctors first suspected meningitis. Aaron was rushed to another hospital in Las Vegas.
Evans tried to reassure his son, but he had no idea what was wrong. On Sept. 17, Aaron stopped breathing as David held him in his arms.
"He was brain dead," David said. Only later did doctors realize the boy had been infected with Naegleria.
"My kids won't ever swim on Lake Havasu again."