Quantification of Human Herpesvirus 6 in Immunocompetent Persons and Post-mortem Tissues from AIDS Patients by PCR

1 Department of Virology, Royal Free Hospital School of Medicine, Rowland Hill Street, London NW3 2PF, UK 2 Histopathology, Royal Free Hospital School of Medicine, Rowland Hill Street, London NW3 2PF, UK and 3 Department of Thoracic Medicine, Royal Free Hospital School of Medicine, Rowland Hill Street, London NW3 2PF, UK Author for correspondence: Vincent C. Eme W. Fax +44 171 830 2854, e-mail vincent{at}rfhsm.ac.uk A quantitative competitive PCR assay for human herpesvirus 6 (HHV-6) was developed. Firstly, viral burden was determined in the blood of 25 healthy persons. Using 1 µg of DNA, the prevalence of HHV-6 was 36% (9/25). Eight persons had viral loads of 32 HHV-6 genomes/µg DNA. The viral burden in the ninth individual was 1·2 x 10 6 HHV-6 genome copies/µg DNA, which remained constant over a period of 10 months. This demonstrates the persistence of a high HHV-6 load in the absence of apparent disease. Secondly, HHV-6 burden was determined in 100 post-mortem tissues from seven AIDS patients and three controls. For all tissues combined, there was a statistically significant higher median viral load in AIDS patients (56 copies/µg DNA, range 0–43 321) compared to controls (10 copies/µg DNA, range 0–423) ( P = 0·04). The precision and reproducibility of this assay will allow hypotheses concerning the pathogenic potential of HHV-6 to be tested quantitatively. Received 20 March 1996; accepted 20 May 1996.