Life cycle of Acanthamoeba species parasitizing humans
Acanthamoeba species have been found in soil; fresh, brackish, and sea water; sewage; swimming pools; contact lens equipment; medicinal pools; dental treatment units; dialysis machines; heating, ventilating, and air conditioning systems; mammalian cell cultures; vegetables; human nostrils and throats; and human and animal brain, skin, and lung tissues. Acanthamoeba life cycles have only two stages, a dormant cyst stage (1) and an actively feeding and dividing trophozoite stage (2) (Acanthamoeba have no flagellated stage). The trophozoites replicate by mitosis (the nuclear membrane does not remain intact) (3). Although the trophozoites are the infective stage, both cysts and trophozoites gain entry into the body (4) through various means. Entry can occur through the eye (5), the nasal passages to the lower respiratory tract (6), or ulcerated or broken skin (7). When an Acanthamoeba enters the eye it can cause severe keratitis in otherwise healthy individuals, particularly contact lens users (8). When it enters the respiratory system or through the skin, it can invade the central nervous system by hematogenous dissemination causing granulomatous amebic encephalitis (GAE) (9) or disseminated disease (10), or skin lesions (11), in individuals with compromised immune systems. Acanthamoeba cysts and trophozoites are found in tissue.
From Centers for Disease Control Parasites and Health website.