Monitoring of active human herpesvirus 6 (HHV-6) infection is important for distinguishing between reactivation and latency of the virus. The reverse transcription polymerase chain reaction (RTPCR) may be a useful tool in order to distinguish active and latent HHV-6 infection. An RT-PCR assay detecting 4 different HHV-6 gene transcripts was established. Samples of peripheral blood mononuclear cells (PBMCs) were collected from patients with exanthem subitum and used to evaluate the reliability of the assay. After confirming the reliability of the assay, RT-PCR was used to determine whether HHV-6 reactivation occurs in children with hypercytokinemia. Three gene transcripts (U31, U39, and U94) were detected in 90-100% of the PBMC samples collected from febrile period of exanthem subitum patients, from which HHV-6 was isolated. The two gene transcripts encoding the late proteins U31 and U39, however, were not detected in samples collected during the convalescent period that contained no infectious virus. The putative latency associated gene transcript, U94, was detected in 2 (10%) of the 20 convalescent samples, and another immediate early gene transcript, U90, was also detected in 3 (15%) of the 20 convalescent samples. The frequency of HHV-6 reactivation in patients with hypercytokinemia, suggesting monocyte/macrophage activation, was studied. Only 9 of 17 patients diagnosed with Kawasaki disease and 1 patient diagnosed with juvenile rheumatoid arthritis were positive for HHV-6 DNA in their PBMCs samples. Neither the U31 gene nor the U94 gene transcript was detected in any of the 10 samples. An RT-PCR assay screening for both immediate early and late genes may be useful for monitoring active HHV-6 infection. No HHV-6 reactivation was found in patients with hypercytokinemia using the RT-PCR assay.
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