Scientists have suggested several factors that might spark the onset of schizophrenia or make it more severe -- hormonal changes, teenage stresses, drug use and even moving from one part of the world to another.
A few think that infections may play a part.
At the University of Pittsburgh, Konasale Prasad has found evidence that schizophrenia patients exposed to the herpes simplex virus perform worse on cognitive tests and have reduced volumes in certain parts of the brain compared with patients who weren't exposed and with healthy control subjects.
While his group must do more research to verify the initial conclusions, Dr. Prasad said there is a physiological foundation for the possible impact of herpes virus on the disorder.
Herpes simplex type 1 infections, which can cause cold sores and even blindness, attack the mucosal linings of the eyes, nose and mouth, and when the virus is active, it also can spread through the trigeminal facial nerve up into the brain and kill off or damage neurons there.
The Pitt group found that herpes-exposed schizophrenia patients had less brain tissue in two key cognitive areas -- the dorsolateral prefrontal cortex, which is involved in planning, and the anterior cingulate, which affects motivation and detection of errors. In another study, schizophrenia patients with antibodies to the virus performed worse on cognitive tests than either their relatives or another group without mental illness.
While he doesn't believe herpes causes schizophrenia, being able to treat it might lessen some effects of the disease, he said. A small study at Pitt showed that treating schizophrenia patients exposed to the infection with an antiviral medication improved some of their memory functions, and he is now involved in a larger study led by colleague Vishwajit Nimgaonkarin in India to see if they can confirm those findings.
E. Fuller Torrey, a schizophrenia researcher at the Stanley Medical Research Institute in Chevy Chase, Md., thinks another infectious agent could be a culprit in at least some cases of schizophrenia -- the toxoplasma parasite.
This tiny bug can be transmitted from cats to humans and can cause brain damage in fetuses, which is one reason pregnant women are advised not to handle cat litter.
Several studies have shown that people with schizophrenia have higher exposure rates to the parasite than people without the disease, Dr. Torrey said, and people who get acute toxoplasma infections as adults sometimes show behaviors similar to those with schizophrenia.
His own theory, which he acknowledged has not yet been proven, is that people who get schizophrenia, as his sister did, have a genetic predisposition to the disease, and "I think the triggers are going to be infectious agents that get into the brain relatively early in life and are triggered in the late teens and early adulthood."
Mark Roth: firstname.lastname@example.org or 412-263-1130.