The boy had meningeal encephalitis -- a combination of meningitis and encephalitis, which causes the brain to swell, according to Dr. Jaime Carrizosa, an infectious disease specialist from Florida Hospital in Orlando. Carrizosa had treated the boy.

Dr. Steven Wiersma of the Florida Department of Health in Tallahassee, says the condition is very rare and has a high mortality rate.

The environmental conditions in Florida lakes -- especially in the hot summer months -- are ideal for amoebas to thrive and proliferate, Carrizosa said.

Amoebas enter the body through the nose. From there, they can travel directly to the brain and into the spinal fluid. That causes brain swelling and the increased pressure is often fatal.

Although patients are given antifungal drugs, "there is no effective treatment," Carrizosa added. "Amoebas have all the possibilities of producing some toxins so there has to be some of that occurring. It's so difficult to study particularly in a critically ill patient."

Although cases are rare, Florida doctors are aware of the danger. "When we have cases of meningitis and there is any history of having been swimming in a lake, diving and going underwater, we immediately look for amoebas in the spinal fluid," Carrizosa said.

The Volusia County Health Department warns against "swimming in lakes, retention ponds or swimming holes, particularly during the hot summer months."

Carrizosa recommends wearing a nose clip and keeping your head above water when swimming in these areas.