Toxoplasmosis, dopamine and schizophrenia

Schizophrenia is a complex neurological disorder, believed to be the results of multiple genetic and environmental factors. One important piece to the puzzle that is schizophrenia is toxoplasmosis. Toxoplamosis is a disease caused by the parasite Toxoplasma gondii. Previous studies have reported that the parasite may play a role in the development of psychotic disorders such as schizophrenia and bipolar disorder. Researchers from the University of Leeds’ Faculty of Biological Sciences (UK) may now be able to tell us the mechanism behind this link. It seems that the parasite infects the brain to form cysts. In producing the cysts, the parasite produces the enzyme tyrosine hydoxylase, a precursor of the neurochemical dopamine. As a neurotransmitter, dopamine plays a very important role in now the brain controls certain aspects of movement, cognition and behaviour. Abnormally high levels of dopamine have been linked to many neurological disorders, including psychosis and schizophrenia.

Dopamine’s role in mood, sociability, attention, motivation and sleep patterns are well documented and schizophrenia has long been associated with dopamine, which is the target of all schizophrenia drugs on the market.

Toxoplasmosis is transmitted via cat feces but can also be food borne. Unwashed vegetables and undercooked infected meat are possible sources of the parasite. It is a fairly common disease. In the US alone, 22% of population has supposedly cysts in the brain. In the UK, it is estimated to be between 10 to 20% of the population. Toxoplasmosis has always been thought to be harmless. Except in infected cases involving pregnant women and those who are immunocompromised (where it can be fatal), the cysts do not cause any harm or symptoms. The recent research results however, suggest that toxoplasmosis may not be as benign as it was originally thought to be.

According to lead researcher Dr Glenn McConkey

“Toxoplasmosis changes some of the chemical messages in the brain, and these changes can have an enormous effect on behaviour. Studies have shown there is a direct statistical link between incidences of schizophrenia and toxoplasmosis infection and our study is the first step in discovering why there is this link.”

Schizophrenia research lags behind compared to research studies on other neurological disorders such as Alzheimer’s disease. With the current knowledge on toxoplasmosis and dopamine, we might be just a bit closer to understanding this complex disease.