and Acanthamoeba spp., are commonly found in lakes, swimming pools, tap water, and
heating and air conditioning units. While only one species of Naegleria,
N. fowleri, is
known to infect humans, several species of Acanthamoeba, including
A. culbertsoni, A. polyphaga, A. castellanii,
A. astronyxis, A. hatchetti, A. rhysodes, A.
divionensis, A. lugdunensis, and A. lenticulata are
implicated in human disease. An additional agent of human disease, Balamuthia mandrillaris,
is a related free-living ameba that is morphologically similar to
Acanthamoeba in tissue sections in light microscopy.
Sappinia is a genus of free-living amebae rarely isolated from humans;
cysts and trophs have been found in the feces of many animals, including
mammals and reptiles.
amebae belonging to the genera Acanthamoeba, Balamuthia, Naegleria
and Sappinia are important causes of disease in humans and animals. Naegleria fowleri
produces an acute, and usually lethal, central nervous system (CNS) disease
called primary amebic meningoencephalitis (PAM). Acanthamoeba spp.
and Balamuthia mandrillaris are opportunistic free-living amebae
capable of causing granulomatous amebic encephalitis (GAE) in individuals
with compromised immune systems. Sappinia diploidea has been
implicated in a case of amebic encephalitis.
Click on genus and species name
above to see specific life cycles of each parasite.
infections appear to occur worldwide.