HCV is a small 50nm， enveloped， single-stranded， positive sense RNAvirus in the family Flaviviridae.
HCV has a high rate of replication with approximately one trillion particles produced each day in an infected individual. Due to lack of proofreading by the HCV RNA polymerase， the HCV has an exceptionally high mutation rate， a factor that may help it elude the host’s immune response. Hepatitis C virus is classified into six genotypes（1-6） with several subtypes within each genotype. The preponderance and distribution of HCV genotypes varies globally. Genotype is clinically important in determining potential response to interferon-based therapy and the required duration of such therapy. Genotypes 1 and 4 are less responsive to interferon-based treatment than are the other genotypes （2， 3， 5 and 6）.
