[Epidemiology of virus-related nervous infections in Japan]

To evaluate the annual incidence of viral CNS infections in Japan, a questionnaire was delivered to the related departments of hospitals and an answer was given from 377 departments (30.2%). Etiological analysis of patients with viral meningoencephalitis indicates that the most (64%) among those with encephalitis diagnosed, is herpes simplex virus (HSV) encephalitis, and the most (89%) among those with viral meningitis diagnosed is non-polio enterovirus (EV) meningitis, followed by mumps virus (MV) meningitis (9%). Epidemiological findings of CNS infections with three viruses, HSV, EV, and MV, are different from each another in age distribution or in seasonal and epidemic incidence, similar to European and American findings, except that with Japanese encephalitis virus (JEV). Infections with JEV decrease recently to 2-39 cases/year by control measures for many years in Japan, though the infections with JEV continue to occur in continental Asian countries. In addition to JE, Japanese travellers abroad should be treated to be protected from infectious diseases absent in Japan, such as rabies.