Sickness and Schizophrenia: Psychotic ills tied to previous infections

Researchers have long suspected that certain childhood infections contribute to the development of schizophrenia by young adulthood, although scarce evidence supports that hunch. Two new studies published in the January American Journal of Psychiatry do just that.

The first investigation found that Swedish youngsters exposed to viral infections of the central nervous system by age 12 displayed elevated rates of psychotic illnesses, including schizophrenia, by ages 17 to 29. Infections with mumps virus or cytomegalovirus showed especially strong links to later psychotic conditions, according to a team led by psychiatrist Christina Dalman of the Karolinska Institute in Stockholm.

Dalman and her coworkers studied a national sample of 1.2 million Swedes born between 1973 and 1985. Government registries recorded their childhood hospitalizations for viral and bacterial infections as well as for psychiatric hospitalizations through 2002 for various mental ailments.

The researchers calculated a slightly increased risk of developing schizophrenia or any of several other psychotic illnesses among individuals who had been treated for viral infections that invade the central nervous system. This finding held after accounting for other factors that raise the chances of developing a psychotic disorder, such as living in a city and having a psychotic parent.

Further analysis revealed that childhood infection with mumps virus roughly doubled the risk for later hospitalization for psychosis. Cytomegalovirus had an even greater effect. Previous evidence indicates that both viruses infect brain cells.

Even in such a large sample, only 23 individuals exposed to childhood viral infections of the central nervous system displayed a psychotic illness later in life. Further studies need to examine how viral infections interact with an individual’s genetic makeup to promote psychosis, the researchers say.

The second study suggests that infection with the common parasite Toxoplasma gondii, carried by cats and farm animals, also boosts a person’s risk of developing schizophrenia.

A team led by epidemiologist David W. Niebuhr of Walter Reed Army Institute of Research in Silver Spring, Md., studied 180 U.S. military personnel discharged because of schizophrenia. For each participant, the researchers analyzed archived blood samples collected before and after physicians diagnosed the severe mental disorder. Niebuhr’s group looked for elevated levels of antibodies that fight toxoplasma infection.

The scientists similarly scrutinized blood collected from 532 military recruits with no psychiatric ailments.

Of those who developed schizophrenia, 7 percent had been infected with the parasite before their diagnosis. Toxoplasma infections affected 5 percent of healthy individuals.

Although that difference appears small, people exposed to toxoplasma experienced a 24 percent greater chance of developing schizophrenia than did those who avoided such infection, the researchers say.

Previous research had identified toxoplasma infections in some people with schizophrenia but hadn’t shown that the infection preceded the mental disorder.

Niebuhr’s team stresses that the parasite may foster schizophrenia only in those genetically predisposed to this mental disorder. Most people infected with toxoplasma never develop schizophrenia.

“Taken together, these two articles provide further evidence that certain infections during childhood and adulthood might be risk factors for schizophrenia,” remarks psychiatrist Alan S. Brown of Columbia University.

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.