What Is the Brain-Eating Amoeba?

Naegleria fowleri is an ameba that CDC says can cause an infection called primary amebic meningoencephalitis, or PAM, if water containing it goes up the nose and to the brain. Typically fewer than 10 people a year in the United States get PAM, and nearly everyone who gets it dies. CDC counts 167 reported US cases between 1962 and 2024, and only four people survived.

How exposure happens. CDC says these infections usually occur after swimming or diving in a lake, river or other fresh water during summer months, often after long hot spells that raise water temperatures and lower water levels, and that a few infections have occurred when people used tap water containing the ameba to rinse their sinuses. You cannot get infected by swallowing water containing the ameba, and the infection does not spread from person to person.

CDC says the first symptoms usually start about 5 days after exposure but can appear anywhere from 1 to 12 days, and early symptoms can include headache, fever, nausea and vomiting. PAM progresses rapidly, with symptoms such as stiff neck, confusion, loss of balance and hallucinations, and most people with it die within 1 to 18 days after symptoms begin.

To lower the risk, CDC advises holding your nose or wearing a nose clip when jumping or diving into fresh water, always keeping your head above water in hot springs, not digging in shallow water where the ameba is more likely to live, and using distilled or boiled tap water when rinsing your sinuses or cleansing your nasal passages.