The parasite that causes toxoplasmosis has been linked to schizophrenia, and biologists in the UK may have discovered why. It seems the organism produces an enzyme that increases the production of the brain chemical dopamine.

Toxoplasma is a parasite, typically carried by cats but which can infect any mammal. People who catch it may develop toxoplasmosis; this is usually a minor illness, although it can be serious when it is passed on by pregnant women to their unborn baby, and it can cause problems in people with impaired immune systems when it infects the brain.

“Several studies have found a statistical correlation of toxoplasmosis with schizophrenia,” one of the authors of the current study, Dr. Glenn A. McConkey at the University of Leeds, explained in an e-mail to Reuters Health. “Hence, someone with schizophrenia is more likely to have toxoplasmosis than the general population.”

On the other hand, other evidence suggests a link between dopamine and schizophrenia, because treatments for schizophrenia, such as haloperidol, block dopamine.

“Ours is the first study showing that the parasite itself could be the source of the neurotransmitter,” commented.

The research is reported in the March issue of the open-access journal PLoS One. The team found the parasite’s genetic make-up included an enzyme that aids in the production of dopamine.

“At this point the research is too premature to suggest changes in treatment” of schizophrenia, McConkey continued. Nonetheless, “Toxoplasmosis screening would be warranted in psychological analysis.”

He and his colleagues now plan to explore the possible role of toxoplasma in other neurological diseases associated with dopamine, including autism, Parkinson’s disease, and Tourette’s syndrome.

SOURCE: PLoS One 2009.