Evolution of hepatitis C virus hypervariable region 1 in chronically infected children.

Hepatitis C virus (HCV) quasispecies diversification plays an essential role in the establishment of chronic infections. Our earlier analysis of HCV population structure in children subjected to interferon-ribavirin treatment demonstrated that viral quasispecies is homogenous in patients who failed to respond to the therapy and heterogeneous in sustained responders. We also showed that certain variants of HCV hypervariable region 1 (HVR1) are conserved in non-responders. To better elucidate the pathways of HCV evolution, here we examined the changes of HVR1 in viral populations isolated from sera of eight treatment-naive pediatric patients. We found that HCV evolution in untreated chronically infected children occurs according to two pathways and results in the formation of either genetically homogenous or variable quasispecies. Variable populations are prone to quasispecies shifts. In contrast, homogenous populations are composed of closely related variants that undergo only minor changes. In addition, we observed that a phenomenon of inter-quasispecies conservation of HVR1 is associated with some of the homogenous HCV populations. The collected data suggest that there exist HVR1 variants with superior fitness, capable of persisting in different hosts.