Genetic heterogeneity of hepatitis C virus

There are four hierarchical strata in the genetic heterogeneity of hepatitis C virus (HCV): group above subgroup above isolates above quasispecies. The entire genome sequence has so far been reported for 16 isolates which are classifiable into 3 groups and 6 subgroups. Provisional classification of HCV is also possible using a partial sequence of the HCV genome. With the E1 region sequence for example, the present collection of HCV isolates can be classified into 9 groups and 23 subgroups. The rationale for these classifications and the epidemiological and clinical implications of genotyping HCV are reviewed.