Real-time PCR determination of human herpesvirus 6 antiviral drug susceptibility

A quantitative real-time PCR assay was developed to determine the antiviral drug susceptibility of human herpesvirus 6 (HHV-6). After short-term culture of the virus, HHV-6 isolates’ susceptibility to the antiviral ganciclovir (GCV) was determined by measuring the HHV-6 variant B (HHV-6B) DNA levels in culture supernatants and infected cells using real-time PCR. A total of 12 well-characterized GCV-sensitive or -resistant strains and clinical isolates were used. This new assay with real-time PCR readout permitted the rapid (3 days), objective, and reproducible determination of HHV-6 drug susceptibilities with no need for stringent control of the initial multiplicity of infection. Furthermore, the real-time PCR assay results showed good correlation (r_s = 0.95) with those from the conventional TCID₅₀ (50% tissue culture infecting dose) reduction assay (TRA). Thus, the real-time PCR assay described in this report was found to be a suitable quantitative method for determining the susceptibility of HHV-6 to antiviral drugs. It is faster and simpler than the TRA, and it is amenable to use in the routine diagnostic virology laboratory.