A rare infection caused by a brain-eating amoeba has taken three lives in the U.S. this summer, CNN reports, and ongoing droughts could put more people at risk. The single-celled killer, known as Naegleria fowleri, is common in lakes and other freshwater sources, and thrives when temperatures are high and water levels are low.

N. fowleri enters through the nose and attacks the brain, usually killing its victim within two weeks, according to the Centers for Disease Control and Prevention. But while the amoeba is widespread, infections are rare because it's not a parasite and doesn't seek out human hosts. It only accidentally ends up in someone's nose, yet once it's there it may burrow into the skull in search of food. When it eats brain tissue, it causes "primary amoebic meningoencephalitis," which is almost always fatal.

About three people die annually from N. fowleri in the U.S., so this year isn't necessarily atypical. But the amoeba is more prevalent in warm, shallow waters — especially in the Southern U.S. — and "infections can increase during heat wave years," according to the CDC.

All three deaths this year have occurred in the South: a 16-year-old girl in Florida, a 9-year-old boy in Virginia and a 20-year-old man in Louisiana. A brutal heat wave and drought have gripped much of the country this summer, and with dry conditions still festering in the South and Plains (see the U.S. drought map below), the threat of N. fowleri could potentially be elevated for weeks in some areas. According to the CDC, infections occur mainly in July, August and September.

People can't be infected with N. fowleri by swallowing contaminated water, the CDC explains; it's only dangerous when it enters via the nose, which offers easy access to the brain. Infections are most common in children and young adults — the median age of victims is 12 — possibly because they're more likely to dive, swim and play in water.

The source of infection is typically a lake, river or hot spring, and the two children who died this summer had both recently been in a lake. The Louisiana man's case was more unusual, though — the Associated Press reports he was infected by tap water he squirted into his nose using a neti pot. Neti pots relieve allergies and sinus problems by washing out the nose and sinuses, but experts recommend disinfecting the water first by boiling or distilling it. Tests showed N. fowleri was living in the Louisiana man's household water pipes, but authorities concluded the contamination was isolated to his house, and found none of the amoebae in local water supplies.

The relative risk of an N. fowleri infection is still extremely low, the CDC points out. There were 32 cases documented in the 10 years from 2001 to 2010, for instance, while there were 36,000 drowning deaths during the 10 years from 1996 to 2005. Yet with such high stakes involved, it's worth being aware of the threat and how to avoid it. Below is a list of symptoms, infection sources and safety tips from the CDC:

Symptoms

Initial symptoms (starting one to seven days after infection) include: headache, fever, nausea, vomiting and stiff neck. Later symptoms include: confusion, lack of attention, loss of balance, seizures and hallucinations. After the start of symptoms, the disease progresses rapidly and usually causes death within one to 12 days.

Infection sources

N. fowleri is not found in the ocean or other saltwater, but it may inhabit the following:

  • Bodies of warm freshwater, such as lakes and rivers
  • Geothermal water, such as hot springs
  • Warm-water discharge from industrial plants
  • Geothermal drinking-water sources
  • Swimming pools that are poorly maintained and/or minimally chlorinated
  • Water heaters with temperatures less than 116º F
  • Soil
Safety tips

As the CDC warns, "The only certain way to prevent a Naegleria fowleri infection is to refrain from water-related activities in or with warm, untreated or poorly treated water." But since a low risk "will always exist with recreational use of warm freshwater," the agency also offers a few tips for minimizing your odds of infection:

  • Avoid water-related activities in warm freshwater during periods of high water temperature and low water levels.
  • Hold the nose shut or use nose clips when taking part in water-related activities in bodies of warm freshwater.
  • Avoid digging in, or stirring up, the sediment while taking part in water-related activities in shallow, warm freshwater areas.
For more information, see the illustration below of N. fowleri's life cycle, and check out the CDC's "Naegleria FAQs" page.

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