This organism is thought to be a sporozoan parasite with some similarities to Toxoplasma. Clinical infection is very frequent in patients who are immunocompromised and is rare otherwise. However, immunocompromise is selective; predominantly conditions that decrease T4 lymphocyte number or function (e.g., HIV-1 and HTLV-I infection, childhood acute lymphoblastic leukemia, and cyclosporin or corticosteroid therapy). […]