The parasite Toxoplasma gondii is thought to be prevalent in humans, although the infection is typically latent. Cats are the definitive hosts of the parasite and it is believed the parasite is transmitted to humans through contact with cat feces. T. gondii is of particular interest to researchers because of its proposed effects on the central nervous system in humans. The parasite is able to enter the central nervous system and affect dopamine metabolism. Increased dopamine levels in infected cells primarily cause changes in the components of the limbic system. This has led to the proposed effects of increased impulsivity and aggression in people with active T. gondii infections. One of the most interesting effects of T. gondii in humans is its proposed contribution to schizophrenia. Schizophrenia alone is not well understood as to what causes the illness. There are studies that have hypothesized an increased level of T. gondii antibodies is correlated with increased risk for development of schizophrenia. This hypothesis is intriguing and requires further investigation.