Severe encephalopathy associated with reactivated human herpesvirus 6 in a six year-old immunocompetent child.

When a six year-old immunocompetent child affected by encephalitis was subjected to virological studies, human herpesvirus 6 variant B2 resulted to be the cause of illness. Laboratory diagnosis based on the finding of human herpesvirus 6 genome in the cerebrospinal fluid of the patient both at the beginning of the disease and on the occasion of a relapse which occurred forty days after the patient's hospital discharge. The presence of high-avidity IgG to human herpesvirus 6 detected in the patient's serum at the time of the first hospital admission proved that he had suffered from a past infection by human herpesvirus 6. In the consequence of this, the human herpesvirus 6 DNA finding in the patient's cerebrospinal fluid was to ascribed to virus reactivation. In the light of virological and serological results, the clinical case described underlines the ability of human herpesvirus 6 to cause neurological disorders not only during primary infections but also during infections supported by rescued virus.