The protozoan Toxoplasma gondii invading the brain. Toxoplasma encephalitis affects patients with defects in antibodies and delayed hypersensitivity as in utero fetuses and AIDS patients.
Toxoplasmosis can be congenital or acquired.
Children and adults with a normal immune system only have minor symptoms if they acquire toxoplasma. However, neonates can develop hydrocephalus, periventricular calcifications, and chorioretinitis if exposed in utero. In HIV infected patients toxoplasma can cause a focal infection in the brain. It usually appears as hemorrhagic and necrotic without a capsule but associated with a considerable amount of edema. Microscopically, toxoplasma has a necrotic appearance with neutrophils, macrophages and a few lymphocytes about it as well as sometimes quite bizarre reactive astrocytes.