Toxoplasmosis is a parasitic disease caused by Toxoplasma gondii, a protozoan that can infect cats, humans and other warm-blooded animals. Infection can occur through consumption of infected meat, by contact with infected animal feces or from mother to child. Most humans are infected through their cats, especially cats with access to the outdoors. Most cases of toxoplasmosis are asymptomatic and not dangerous; about half of the world's adult population carries this virus.

Pregnant women and people with weakened immune systems can be in danger from toxoplasmosis, however. While the disease causes no symptoms or mild, flu-like symptoms in the majority of people, it can cause inflammation of the brain, heart, liver, eyes and inner ears in at-risk patients. Toxoplasmosis can also cause neurological problems and has been linked with obsessive-compulsive disorder, schizophrenia, ADHD and brain cancer. 

Diagnosis of toxoplasmosis can be very difficult, since it is hard to distinguish from lymphoma of the central nervous system. Many doctors don't test for this disease at all. Instead, the treat it using pyrimethamine, leucovorin and sulfadiazine and take a biopsy if symptoms don't disappear. Tests are available for pregnant women and some people with weak immune systems. These tests detect the antibodies produced in reaction to the virus. Normal results in adults are less than 1:64 titers for IgM antibodies and less than 1:1024 for IgG.