Life cycle of Naegleria fowleri parasitizing humans
The life cycle of Naegleria fowleri has three stages: cysts (1), trophozoites (2), and flagellated forms (3). The trophozoites replicate by promitosis (the nuclear membrane remains intact) (4). Naegleria fowleri is found in fresh water, soil, thermal discharges of power plants, heated swimming pools, hydrotherapy and medicinal pools, aquariums, and sewage. Trophozoites can turn into temporary non-feeding flagellated forms which usually revert back to the trophozoite stage. Trophozoites infect humans or animals by penetrating the nasal mucosa (5) and migrating to the brain (6) via the olfactory nerves causing primary amebic meningoencephalitis (PAM). Naegleria fowleri trophozoites are found in cerebrospinal fluid (CSF) and tissue, while flagellated forms are occasionally found in CSF. Cysts are not seen in brain tissue.
From Centers for Disease Control Parasites and Health website.