Naegleria fowleri is a free-living amoeba that can cause a rare and often fatal infection of the brain called primary amoebic meningoencephalitis (PAM). The amoeba is found in warm freshwater environments, such as lakes, rivers, and hot springs, and can enter the body through the nose when an individual swims or dives in contaminated water.

Once inside the body, Naegleria fowleri travels up the olfactory nerve to the brain, where it causes inflammation and destruction of brain tissue. Symptoms of PAM typically develop within 1 to 7 days of exposure, and can include headache, fever, nausea, vomiting, stiff neck, seizures, and hallucinations. The infection progresses rapidly, and can cause death within a matter of days.

PAM is a rare infection, with only a few dozen cases reported in the United States over the past several decades. However, the infection is highly lethal, with a mortality rate of over 95%, and there are no known effective treatments.

Prevention of PAM involves avoiding exposure to warm freshwater sources that may be contaminated with Naegleria fowleri. This can include wearing a nose clip or avoiding activities such as diving and jumping into warm bodies of water. In addition, individuals can reduce their risk of infection by keeping swimming pools and hot tubs clean and properly maintained, and by avoiding putting their heads underwater in bodies of water that are known to be contaminated with the amoeba.