Brain

Cryptoccoccal Menigitis — This is a yeast-like fungus infection that usually involves the brain and lungs, although it can affect almost any organ. The fungus that causes this condition is found in soil throughout the world. It is most common in soil contaminated by bird droppings. This disease is most often occurs when a person's CD4+ T cell count falls below 100 cells per cubic millimeter of blood.
HIV-related Encephalopathy — Encephalopathy is a term for diseases that alter brain function or structure, leading to problems with cognitive function, or mental processes, and memory. In people with HIV and AIDS, encephalopathy is usually caused by an infectious agent, such as a bacteria, virus or prion. Encephalopathy most often occurs when a person's CD4+T cell count falls below 50 cells per cubic millimeter of blood. Toxoplasma-seropositive patients who have a CD4+T cell count of less than 100 cells per cubic millimeter of blood should be treated with prophylaxis to prevent developing encephalopathy.
Progressive Multifocal Leukoencephalopathy (PML) — Progressive multifocal leukoencephalopathy (PML) is a rare disorder of the nervous system caused by a common human polyomavirus, JC virus. It leads to the destruction of the myelin sheath that covers nerve cells. The myelin sheath is the fatty covering that acts as an insulator on nerve fibers in the brain. Symptoms include mental deterioration, vision loss, speech disturbances, inability to coordinate movements, paralysis and ultimately coma. In rare cases, seizures may occur. This disease can occur when the CD4+T cell count falls below 200 cells per cubic millimeter of blood.
Toxoplasmosis — This condition occurs when a parasite infects the brain. Symptoms include confusion or delusional behavior, severe headaches, fever, seizures and coma. It can affect the eye, causing eye pain and reduced vision and is most likely occurs when the CD4+ T cell count falls below 100 cells per cubic millimeter of blood. Preventative treatment — usually with trimethoprim-sulfamethoxazole, also called Septra and Bactrim — may be administered when the CD4+ T cell count falls below 100 cells per cubic millimeter of blood.