Amebic Meningitis: The Rare Infection Caused by Naegleria fowleri

Primary amebic meningoencephalitis (PAM) is a rare brain infection caused by Naegleria fowleri, a free-living ameba, a single-celled organism too small to see without a microscope, sometimes called the "brain-eating ameba." Only a few people are diagnosed with PAM in the United States each year. It can be treated with medicines, but most people do not survive.

Symptoms

At first, PAM looks like typical meningitis, with headache, fever and a stiff neck. After symptoms start, it progresses quickly. Death usually occurs within 5 days (range 1 to 18 days) of the first symptoms, and only a few people in the United States have survived.

Anyone with symptoms of meningitis should see a health care provider right away, especially after recently swimming in warm fresh water.

Where it lives and how people are infected

N. fowleri lives in warm fresh water and soil around the world. Infections often follow long hot spells, when water is warmer and water levels lower.

• Fresh water: most infections happen when people swim or put their heads under water in warm lakes, ponds or rivers.
• Tap water: infection can also occur when people rinse their sinuses with contaminated tap water, for religious or health reasons. Very rarely, people have been infected at splash pads or surf parks without enough chlorine.
• Geography: in the United States, most infections have been linked to swimming in warm southern states, but evidence suggests the ameba's range is spreading north as the climate warms.

The ameba enters the body through the nose, usually while swimming, travels up to the brain, destroys brain tissue and makes the brain swell. People cannot be infected by drinking contaminated water, and the infection does not spread from person to person.

Lowering your risk

• Hold your nose or wear a nose clip when jumping or diving into fresh water.
• Always keep your head above water in hot springs.
• Don't dig in shallow water, where the ameba is more likely to live.
• Use distilled or boiled tap water to rinse your sinuses or nasal passages.

Diagnosis and treatment

PAM is hard to diagnose because it is so rare and its early symptoms, such as fever and headache, resemble other illnesses. Laboratory tests can detect the ameba in spinal fluid. Several drugs work against it in the laboratory, but how well they work in patients is unclear, because almost all infections have been fatal, even with treatment.

Sources

• Centers for Disease Control and Prevention, "About Amebic Meningitis." https://www.cdc.gov/meningitis/about/amebic-meningitis.html
• CDC, "About Naegleria fowleri Infections": https://www.cdc.gov/naegleria/about/index.html; causes and risk: https://www.cdc.gov/naegleria/causes/index.html; prevention: https://www.cdc.gov/naegleria/prevention/index.html