A rare infection of the brain and meninges caused by free-living amebae. The organisms invade the nasal mucosa of persons swimming in fresh water, the natural habitat of Acanthamoeba and Naegleria fowleri. The organisms invade the central nervous system through the olfactory foramina. The symptoms begin after an incubation period of 2 to 15 days and are those of acute meningitis. Debilitated or immunocompromised persons are esp. susceptible. Diagnosis is made by finding the amebae in the spinal fluid. Treatment is virtually ineffective and most patients die within a week of onset. Swimming pools adequately treated with chlorine are not a source of the amebae.