Toxoplasma gondii is a parasite that lives in the intestines of cats, shedding eggs that can be picked up by rats and other animals. Humans and other animals can be hosts to Toxoplasma as well. People get infected by its eggs by handling soil or kitty litter. It is thought that for most people the parasite lives “quietly” in their bodies including the brain, and about half of the world’s population is infected. Toxoplasmosis is only an immediate threat for people with low defenses (i.e. AIDS, pregnancy).
In general, healthy rats get anxious with the odor of cat urine and they shy away from it, making them more cautious. But scientists at Oxford discovered that Toxoplasma changes this self-preserving mechanism in rats, making them more likely to get themselves killed. The scent of a cat didn’t make them anxious or cautious. Instead, they even took a special interest in the odor and came back to it repeatedly.
The scientists speculated that Toxoplasma was capable of secreting a substance that was altering the patterns of brain activity in the rats. Given the similarity between the basic anatomy and brain chemical activity between rats and humans, the question then became if toxoplasmosis could alter human behavior as it did with our formerly cautious rats. Furthermore, a link between schizophrenia and toxoplasmosis has been made which was confirmed with recent research where it was proven that toxoplasmosis changes some of the chemical messages in the brain. These chemical changes can have an enormous effect on human behavior. The parasite infects the brain producing an enzyme called tyrosine hydroxylase, which is needed to make dopamine. Dopamine’s role in mood, sociability, attention, motivation and sleep patterns are well documented, and it also has an important role in schizophrenia: