Japanese encephalitis in a 7-month-old Japanese boy.

A 7-month-old Japanese boy was diagnosed as having meningo-encephalitis with anterior horn cell damage. The complement fixation (CF) and hemagglutination inhibition (HI) tests showed increased antibody titers against Japanese encephalitis (JE) virus, but HI antibody in the mother's serum was not increased. It appears that the lack of JE-antibodies from the mother may have resulted in increased JE viral infectivity in the patient. A decrease in the incidence of antibodies against various viruses in women of childbearing age may lead to increased rates of severe viral infection in infants.