Most protozoa are free-living and have little or no impact on human health. They are found throughout the environment, particularly in soil and water. However, there are four free-living amoeba that have been associated with serious human infections. They are known as amphizoic amoebae because they not only have the ability to exist as free-living organisms in nature, but on rare occasions, may invade a host and live as parasites within the host’s tissue. These four free-living amoeba belong to the genera Naegleria, Acanthamoeba, Balamuthia, and Sappinia.
This review will primarily focus on the epidemiology, life cycle, possible mechanism of infection, illness and symptoms, diagnosis, treatment, and prevention of three of these free-living amoeba. To date, only one human infection of Sappinia species has been reported in the United States. In 1998, a healthy 38-year-old man from Texas was diagnosed with an infection of the brain caused by Sappinia pedata (a free-living amoeba) and survived. While the biology is fairly well understood, aspects regarding this organisms' infective capabilities need further research. Consequently, any further discussion of this organism would be premature.