Toxoplasmosis is a disease caused by the organism Toxoplasma gondii. Toxoplasmosis usually affects the brain and causes a disease called toxoplasma encephalitis. The organism can infect and cause disease in other organs, including the eyes and lungs.
Common sources of this organism include cats or birds, and undercooked meat, especially pork, lamb, or venison. While cats or birds that test negative for toxoplasmosis and remain housebound are not a risk, those that go outside can carry toxoplasma back into the house or apartment. Handling either bird droppings or kitty litter than contains cat droppings is a major source of infection.
Toxoplasma encephalitis can occur in patients who have antibodies to Toxoplasma gondii—which indicates that the infection is present in the body. It is a rare disease among HIV-positive people with CD4 cell counts above 200, and is most common among HIV-positive people with CD4 cell counts below 50. Luckily, some of the treatments used to prevent Pneumocystis pneumonia (PCP), especially TMP-SMX (Bactrim, Septra), have been shown to effectively prevent toxoplasmosis from causing disease.