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Journal of Clinical Microbiology, April 2007, p. 1298-1304, Vol. 45, No. 4
0095-1137/07/$08.00+0     doi:10.1128/JCM.02115-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Human Herpesvirus 6 DNA Levels in Cerebrospinal Fluid Due to Primary Infection Differ from Those Due to Chromosomal Viral Integration and Have Implications for Diagnosis of Encephalitis

Katherine N. Ward,^1* Hoe Nam Leong,² Anton D. Thiruchelvam,¹ Claire E. Atkinson,² and Duncan A. Clark^2,

Centre for Virology, Division of Infection and Immunity, Royal Free and University College Medical School, UCL Campus, Windeyer Institute of Medical Sciences, 46 Cleveland Street, London W1T 4JF, United Kingdom,¹ Centre for Virology, Division of Infection and Immunity, Royal Free and University College Medical School, Hampstead Campus, Rowland Hill Street, London NW3 2PF, United Kingdom²

Received 17 October 2006/ Returned for modification 11 December 2006/ Accepted 5 January 2007

The prevalence and concentration of human herpesvirus 6 (HHV-6) DNA in the cerebrospinal fluid (CSF) of the immunocompetent in primary infection was compared with that in viral chromosomal integration. Samples from 510 individuals with suspected encephalitis, 200 young children and 310 older children and/or adults, and 12 other patients were tested. HHV-6 DNA concentration (log₁₀ copies/ml) was measured in CSF, serum, and whole blood using PCR. Serum HHV-6 immunoglobulin G antibody was measured by indirect immunofluorescence. Primary infection was defined by antibody seroconversion and/or a low concentration of HHV-6 DNA (<3.0 log₁₀ copies/ml) in a seronegative serum. Chromosomal integration was defined by a high concentration of viral DNA in serum (3.5 log₁₀ copies/ml) or whole blood (6.0 log₁₀ copies/ml). The prevalences of CSF HHV-6 DNA in primary infection and chromosomal integration were 2.5% and 2.0%, respectively, in the young children (<2 years) and 0% and 1.3%, respectively, in the older children and/or adults. The mean concentration of CSF HHV-6 DNA in 9 children with primary infection (2.4 log₁₀ copies/ml) was significantly lower than that of 21 patients with viral chromosomal integration (4.0 log₁₀ copies/ml). Only HHV-6B DNA was found in primary infection, whereas in viral integration, 4 patients had HHV-6A and 17 patients HHV-6B. Apart from primary infection, chromosomal integration is the most likely cause of HHV-6 DNA in the CSF of the immunocompetent. Our results show that any diagnosis of HHV-6 encephalitis or other type of active central nervous system infection should not be made without first excluding chromosomal HHV-6 integration by measuring DNA load in CSF, serum, and/or whole blood.

Published ahead of print on 17 January 2007.

Present address: Virology, Barts and the London NHS Trust, 80 Newark Street, London E1 2ES, United Kingdom.

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