(Images depict the growth cycle of the A. castellanii parastite before it reaches the infected form or trophozoites stage.)

Acanthamoeba castellanii can be found clustered together in soil ecosystems.  It preys on
bacteria, fungi and other protozoa.  It is considered to be a host for the bacteria, called Legionella pneumophila, is said to be responsible for Legionnaires' disease, which is a pneumonia-like illness where the lungs become severly inflammed.  A. castellanii is a free-living amoeba isolated from aquatic environments.  This organism is one of the very few well-studied members of this group of amoebae.  It characterizes itself by forming a thick-walled cyst that is resistant to any environmental condition, and is a pathogen that can cause severe encephalitis in humans with a weakened immune system.

Granulomatous amoebic encephalitis caused by the A. castellanii parasite is a serious human infection with fatal consequences but it is unclear as to how the circulating parasite interacts with the blood-brain barrier; passes through it to get to the central nervous system or in other words transmigrates.

Chlamydia pneumoniae is a cellular respiratory pathogen, which is similar to Legionella, is also considered to be a host for A. castellanii.