Excerpt from Blaser, John Bennett, Raphael Dolin, Martin J. Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases – Electronic. Available from: Elsevier eBooks+, (9th Edition). Elsevier – OHCE, 2019.
Despite the hundreds of species of free-living amoebas that are known, only a few have been reported to infect humans. 169 – 173 The most important are in the genera Naegleria, Acanthamoeba, and Balamuthia. Naegleria fowleri, the main protozoan causing primary amebic meningoencephalitis (PAM) in humans, has been recovered from lakes, puddles, pools, ponds, rivers, sewage sludge, tap water, air conditioner drains, and soil. Sporadic cases of PAM occur when persons, usually children and young adults, swim or play in water containing the amebas or when swimming pools or water supplies have become contaminated, often through failure of chlorination. In one review of 111 cases reported in the United States from 1962 to 2008, cases were reported in most southern states and occurred primarily in previously healthy young males exposed to warm recreational waters, especially lakes and ponds, in warm weather locations during summer months. 172 Activities that increase insertion of water into the nasal cavities (e.g., water skiing and wakeboarding) may increase the risk for developing PAM. 173 Asymptomatic carriage by humans can also occur. Several cases have been reported in HIV-infected patients, all with advanced HIV disease at the time of amebic infection. 174