Acanthamoeba spp. as opportunistic pathogens parasites Among free-living amoeba in nature, species of the genus Acanthamoeba have been associated with human disease.These amoeba are among the most abundant protozoa in nature due to its cosmopolitan distribution and are able to survive in a wide variety of habitats because its low demand for food and in harsh environments by forming structures known as cysts.However, ecological changes and incursion of its different habitats have made this organism can invade a host and live as parasites within him.That's why this type of protozoa are known as amphizoic organism, because human can be constituted as its host, causing infections in the central nervous system, disseminated infections in skin and lungs, and keratitis.Thus, since an increase in the number of cases of Acanthamoeba infections has occurred worldwide, these protozoa have become increasingly important as agents of human disease.This review summarizes what is known of this kind of free-living amoeba, focusing on the biology, ecology, pathogenesis, diagnosis, treatment and human defense mechanism against infection by the amoeba.