Jack Herrara, aged 12, died after his brain was attacked by the Naegleria fowleri amoeba after swimming in a lake; three of the other victims were in Florida and one was in Arizona.
Recent tests have shown that the brain-eating amoeba is present in Tucson's water supply, but experts say the microscopic bug does not pose any health risks because before distribution the water is chlorinated, which kills Naegleria fowleri before the water reaches the taps.
The U.S. Centre for Disease Control and Prevention (CDC) says Naegleria fowleri is found worldwide, most commonly in warm bodies of freshwater, such as lakes, rivers, hot springs, water discharged from industrial plants, poorly maintained and minimally chlorinated swimming pools and in the soil.
Between 1995 and 2004 only 23 infections were documented in the U.S. and though infection with naegleria is very rare, it occurs most commonly during the dry, summer months, when the air temperature is hot, the water is warm, and water levels are low.
The CDC says the number of infections increase during heat waves.
The infection occurs when the amoeba enters the body through the nose, usually when people are swimming underwater, diving, or doing water sports that result in water going up the nose. The amoebae then travel to the brain and spinal cord where it destroys the brain tissue.
The signs and symptoms of naegleria begin 1 to 14 days after infection and include headache, fever, nausea, vomiting, and a stiff neck.
As the amoebae cause more extensive destruction of brain tissue this leads to confusion, lack of attention to people and surroundings, loss of balance, seizures, and hallucinations.
After the onset of symptoms, the disease progresses rapidly and usually results in death within three to seven days.
The early symptoms associated with naegleria are similar to other more common illnesses, such as meningitis and people should seek medical care immediately if they develop a sudden onset of two or more of the early symptoms (e.g., fever, headache, stiff neck) at the same time or if symptoms are unusually severe.
Although several drugs appear to be effective against naegleria in the laboratory and a variety of treatments have been used to treat infected persons, most infections have still been fatal.
Naegleria infection cannot be spread from person-to-person contact.
Charles Gerba, a microbiology professor with the University of Arizona's Department of Soil, Water and Environmental Science, who is conducting a study on Naegleria fowleri says it feeds on bacteria and is everywhere.
