Varicella zoster virus quantitation in blood from symptomatic and asymptomatic individuals

Primary infection with Varicella zoster virus (VZV) occurs in immunocompromised and immunocompetent individuals. Clinical and asymptomatic reactivation with shedding of infectious virus and viremia may occur. The prevalence of VZV viremia is unknown. The aim of this study was to detect VZV viremia and quantify VZV DNA using quantitative polymerase chain reaction (qPCR) in blood from different populations. A qPCR-based method using EvaGreen^® was used to quantify VZV DNA in 491 samples, including whole blood, plasma and buffy-coat, from patients hospitalized with varicella-associated disease (Group 1, n=10) and three groups with no VZV disease: individuals with a first clinical diagnosis of central nervous system demyelination (Group 2, n = 213) with their age and sex-matched controls (Group 3, n = 218); and HIV-infected individuals (Group 4, n = 50). VZV-specific IgG antibody titres were measured in Group 3. The proportion positive for viremia and mean detectable VZV DNA load (copies/ml) were: Group 1: 100% (10/10) and 4.6 × 10⁶ ± 1.4×10⁷; Group 2: 4% (9/213) and 1.5 × 10³ ± 1.8 × 10⁴; Group 3: 8% (17/218) and 1.1 × 10³ ± 7.8 × 10³; Group 4: 12% (6/50) and 7.7 × 10¹ ± 2.8 × 10² . VZV DNA load and IgG titres were not significantly correlated (Group 3 only). VZV load in Group 1 was significantly elevated compared to Groups 2-4 (P < 0.001); the latter were not significantly different from each other (P = 0.05). VZV genotypes from clades 1-5 were identified in Group 1. VZV DNA was detected but at low frequency and viral load in both immunocompetent and immunocompromised individuals asymptomatic for VZV infection, compared to individuals with active VZV infection.