viral hypothesis
the theory, first suggested in the early 20th century, that psychoses resembling schizophrenia are associated with influenza epidemics. It was later observed that several types of viral encephalitis may involve schizophrenia-like symptoms, and many studies have investigated the effect of exposure to viral agents, especially in utero, on subsequent development of schizophrenia. In particular, U.S. psychiatrist E. Fuller Torrey (1937– ) has noted that the viral hypothesis accounts for the greater number of people with schizophrenia born from January to April (see seasonality effect), a period during which there is a high incidence of viral infections. More recently, however, it has been suggested that virus exposure is a risk factor for—rather than a key causative event in—the development of schizophrenia.