Viral causes of psychiatric disease.

Current evidence on the role of viruses in the causation of psychiatric illness is reviewed. Herpes simplex encephalitis is relatively well defined but a wider role for this virus, particularly in relation to affective disorders, is suggested by some Scandinavian surveys of antibody titres in psychiatric populations. The extent to which influenzal illnesses and infectious mononucleosis may lead to neurotic, and occasional psychotic, episodes is the subject of controversy. The clinical literature is reviewed on the occurrence of encephalitis-like illnesses with prominent psychiatric and behavioural features. It is pointed out that no reliable criterion exists for differentiating these illnesses from such psychiatric syndromes as schizophrenia. It is suggested that neglect of this borderland area, and perhaps preconceptions concerning the features of 'organic' and 'functional' psychiatric disease, may have led to an underestimate of the possible role of viruses in the causation of psychiatric disease.