2:54 PM EDT, August 17, 2011
BREVARD COUNTY, FL -- Three people have died this summer after suffering rare infections from a waterborne amoeba that destroys the brain.
This is the time of year when there is an uptick in cases.
The amoebas flourish in the heat -- especially during the summer months in the South, thriving in warm waters where people swim.
Health officials usually record about two to three cases in a given year -- 1980 was the highest with eight deaths.
And most of the time, they occur in children and teenagers.
"These are rare infections, but super tragic for families," said Jonathan Yoder, the waterborne disease and outbreak surveillance coordinator at the Centers for Disease Control and Prevention.
"We don't want to minimize how hard it is for families."
The amoeba, called Naegleria fowleri, is the only type that infects humans and is more than 95% lethal.
The first death in 2011 occurred in June in Louisiana, according to the CDC.
The most recent involved a 16-year-old girl who died Saturday after becoming infected by an amoeba in Brevard County, Florida, according to CNN's affiliate WFTV.
The amoeba could have entered the teen's body as the teen swam in a nearby river.
The central Florida station reported that the teenager had suffered fever, nausea and headaches.
A spinal tap showed that Naegleria fowleri was present in her spinal fluids.
In another case, the Virginia Department of Health confirmed Friday that a child from central Virginia died from primary amoebic meningoencephalitis, which is caused by the amoeba.
The Richmond Times Dispatch said the child was a 9-year-old boy from Henrico County.
The child died within the last few weeks, said Dr. Keri Hall, the state's director of epidemiology.
She declined to share other details. Virginia's last confirmed case was in 1969.
Amoeba infections in humans are extremely rare.
The CDC found 32 reported cases in 10 years -- compared with 36,000 drowning deaths from 1996 to 2005.
Rare but deadly amoeba infection hard to prevent
The median age of the victims is 12, possibly because children and teenagers are more likely to play and swim in water.
Nearly two-thirds of those killed by the amoeba are children under the age of 13.
The amoebas enter the human body through the nose after an individual swims or dives into warm fresh water, like ponds, lakes, rivers and even hot springs.
Lurking in fresh waters during the summertime, they're more likely to infect humans in July, August and September.
It's unclear why out of the millions of people who swim in the same fresh waters, a small fraction of people are infected by the amoeba.
"It's difficult to know," Yoder said. "It's not a disease that's easy to study because the end result is so severe. It's difficult to study in the lab."
Scientists speculate that the lack of certain antibodies could be why some children get infected, while others who've swum in the same water don't, said Francine Cabral, professor of microbiology at Virginia Commonwealth University School of Medicine.
The amoeba is not a parasite. A human is an "accidental end point for the amoeba after it's forced up the nose," Yoder said. It does not seek human hosts.
But when an amoeba gets lodged into a person's nose, it starts looking for food. It ends up in the brain and starts eating neurons.
"It causes a great deal of trauma and a great deal of damage," Yoder said. "It's a tragic infection. It's right at the frontal lobe. It affects behavior and the core of who they are -- their emotions, their ability to reason -- it's very difficult."
Early symptoms include headache, fever, nausea, vomiting and neck stiffness. Later symptoms include confusion, lack of attention to people and surroundings, loss of balance, seizures and hallucinations.
The amoeba multiplies, and the body mounts a defense against the infection. This, combined with the rapidly increasing amoebas, cause the brain to swell, creating immense pressure. At some point, the brain stops working.
Death typically occurs three to seven days after the symptoms start.
At hospitals, the infection is often mistaken for bacterial meningitis. Even when the diagnosis is made, the infection is difficult to treat.
The primary treatment for Naegleria infection is amphotericin B, an antifungal medication injected into the veins and brain.
But so far, only one person -- back in 1978 -- is known to have survived an infection, Yoder said.
Here are the CDC's tips for prevention:
* Refrain from activities in warm, untreated or poorly treated water, especially when water levels are low and temperatures are high.
* Hold the nose shut or use nose clips when swimming in warm fresh water.
* Avoid digging or stirring up underwater sediments while submerged in shallow, warm freshwater areas.