Herpes simplex encephalitis.

Herpes simplex encephalitis is a rapidly progressive disease in neonates and adults. Mortality is high, and there are severe neurologic sequelae in survivors. The reasons for centripetal transfer of virus to the brain are not fully understood. Prompt diagnosis followed by antiviral therapy with acyclovir significantly improves the prognosis. Controversy surrounds the need for brain biopsy before antiviral therapy is started.