Encephalitis refers to an acute, usually diffuse, inflammatory process affecting the brain. While meningitis is primarily an infection of the meninges, a combined meningoencephalitis may also occur. An infection by a virus is the most common and important cause of encephalitis, although other organisms may sometimes cause an encephalitis. An encephalitic illness caused by alteration of normal immune function in the context of a previous viral infection or following vaccination is also well recognised (acute disseminated encephalomyelitis, ADEM). An infectious encephalitis may also be difficult to distinguish from an encephalopathy that may be associated with numerous metabolic causes. Among the factors which have helped to focus attention on viral encephalitis over the last few years have been:
the development of effective antiviral agents for this condition, most notably acyclovir for herpes simplex virus encephalitis (HSE) which is caused by herpes simplex virus (HSV)-1 or HSV-2
the advent of human immunodeficiency . .
