Different characteristics of human herpesvirus 6 encephalitis between primary infection and viral reactivation

Background: Pathogenesis of human herpesvirus 6 (HHV-6) encephalitis, in particular difference between HHV-6 encephalitis at the time of primary infection and reactivation remains unclear. Objectives: To elucidate the mechanism of HHV-6 encephalitis at the time of primary infection and reactivation. Study design: Twenty-two HHV-6 encephalitis patients at the time of primary infection, 6 febrile convulsion (FC) patients caused by HHV-6 infection, and 14 FC patients without HHV-6 infection (non HHV-6 FC) were enrolled. Additionally, 7 stem cell transplant recipients with HHV-6 encephalitis and eight adult controls were also enrolled in this study. Cerebrospinal fluid (CSF) HHV-6 DNA copy numbers and biomarkers levels were compared. Results: Low copy number of CSF HHV-6 DNA was detected in 7 of the 22 patients with HHV-6 encephalitis in primary infection, whereas all seven CSF samples collected from post-transplant HHV-6 encephalitis patients contained high viral DNA copy numbers (P< 0.001). CSF concentrations of IL-6 (P = 0.032), IL-8 (P = 0.014), MMP-9 (P = 0.004), and TIMP-1 (P = 0.002) were significantly higher in patients with HHV-6 encephalitis in primary infection than non-HHV-6 FC. CSF IL-6 (P = 0.008), IL-8 (P = 0.015), and IL-10 (P = 0.019) concentrations were significantly higher in patients with post-transplant HHV-6 encephalitis than adult controls. Conclusion: The present study suggests that the characteristics of HHV-6 encephalitis are different between HHV-6 encephalitis at the time of primary infection and reactivation in transplant recipients.