[Herpes viruses--herpes simplex virus, varicella-zoster virus, EB virus, cytomegalovirus].

Herpes simplex encephalitis is the commonest viral encephalitis among individuals, and the mortality has been markedly decreased by the use of vidarabine and acyclovir. Early diagnoses and immediate treatment are essential for favorable prognoses. Neuro-imagings, such as MRI and SPECT, and PCR technique for detection of HSV-DNA in CSF, are useful for early diagnoses, without requiring brain biopsy. Varicella and herpes zoster viruses are complicated, only rarely, with neurological manifestations, such as meningoencephalitis, myelitis, or peripheral neuropathy. Acyclovir is mostly effective in these cases. Neurological complications of Epstein-Barr virus infections are variable, including meningitis, cerebellar ataxia, cranial neuropathy, and Guillain-Barré syndrome. Their prognoses are generally good. Cytomegalovirus encephalitis is one of the common complications in AIDS patients. Its clinical diagnosis is difficult and the prognosis is considered to be poor.