Hepatitis C viral quasispecies.
Analysing significant numbers of cDNA clones of the hepatitis C virus (HCV) from single isolates provides unquestionable proof that the viral genome cannot be defined by a single sequence, but rather by a population of variant sequences closely related to one another. This way of organizing the genetic information is referred to as quasispecies. Throughout HCV infection, the number and composition of the variants in the viral population keeps changing owing to environmental influences, resulting in a virus that is constantly redefining itself both genetically and phenotypically. Therefore, the virus has often been investigated in population terms. Many clinical studies have tried to unravel, through the parameters that characterize the HCV quasispecies, prognostic markers of the disease and its response to treatment. Other investigations have focused on discovering how the virus and host interact during chronic infection. The consensus sequence, the rate of fixation of mutations and the complexity of the viral population are useful parameters for describing the viral population behaviour and its interaction with the host. In addition to sequencing, several other methods, based on electrophoretic mobility, have been used to study these parameters, such as temperature gradient-gel electrophoresis, single-strand conformation polymorphism and gel-shift analysis. The viral region examined, the source of clinical specimen, as well as the methodology employed, will be decisive in interpreting the information obtained.