Encephalitis, Viral

Encephalitis is inflammation and swelling of the brain, often caused by an acute viral infection, or a para- or postinfectious phenomenon known as acute disseminated encephalomyelitis (ADEM). The most common sporadic viral cause is herpes simplex virus, but arthropodborne viruses, such as Japanese encephalitis virus, are a major cause in some settings, and rabies in others. Herpes simplex encephalitis is treated with acyclovir; rabies and Japanese encephalitis are preventable with vaccines. With the reduction in measles through vaccination, the incidence of ADEM, which often follows measles, has also reduced.