The possible viral causes of acute infectious encephalitis have
already been listed in table 1. There are also numerous nonviral
causes of infectious encephalitis comprising various
bacteria, rickettsia, fungi, and parasites; these are broadly,
but not exhaustively, summarised in table 5. The general
diagnostic approach to the differential diagnosis which I shall
outline here is straightforward, and consists of the history,
examination and then general and neurological investigations.
However, it should be appreciated that in approximately
half of cases the cause of viral encephalitis is not
found.