Wide Range of Quasispecies Diversity during Primary Hepatitis C Virus Infection

Hepatitis C virus (HCV) infections may be initiated by multiple infectious particles, resulting in a genetically heterogeneous viral population, or by a single particle, leading to a clonal population in the initial stage of infection. To determine which of these scenarios is most common, we evaluated the genetic diversity of HCV quasispecies in 12 seronegative subjects with primary infection following community exposures, six acutely infected recipients of HCV-seropositive blood transfusions and six seropositive individuals with infections of undetermined durations. RNA isolated from plasma and a region of the HCV envelope gene including the first hypervariable region (HVR-1) was reverse transcription-PCR amplified and subcloned, and multiple plasmid clones were sequenced. Phylogenetic analysis indicated that all HCV variants clustered by individuals. Genetic distances among HCV variants within recently infected subjects ranged from 1 to 7.8%. On the basis of the estimated mutation rate of HCV in vivo and the Taq polymerase error rate, primary infection viral quasispecies were classified as genetically heterogeneous when the maximum sequence divergence between genetic variants in the same person was >3%. Heterogeneous quasispecies were detected in 4 of 12 preseroconversion subjects, 1 of 6 transfusion recipients, and 4 of 6 seropositive subjects. The high level of viral quasispecies genetic diversity found in at least a third of recently infected individuals is consistent with the transmission of multiple infectious particles. Community-acquired HCV infection, predominantly the result of needle sharing by injection drug users, therefore appears to be frequently initiated by the successful transmission of multiple viral variants.