Acanthamoeba
The free-living amoebae that cause human infections include Acanthamoeba, Naegleria, Balamuthia mandrillaris, and Sappinia diploidea. All 4 genera cause CNS infections that are frequently fatal. These amoebae are distinct from other pathogenic protozoa. They all have a free-living existence, have no human carrier state (which is important in disease transmission), have a limited relationship with the spread of infection and poor sanitation, and have no insect vector.