Mechanisms of viral emergence

Domingo, Esteban

Once established, additional adaptive mutations are likely to occur while the virus completes its infectious cycle in the target cells and organs of the newly invaded host. There have been many descriptions that viruses replicating either in cell culture or in vivo, when given the opportunity, increase their replicative fitness [21, 59, 60] . Fitness increase is the expected response when a virus maintains replicative competence in a new environment, or when it escapes from natural (neutralizing antibodies or cytotoxic T cells) or artificial (antiviral drug) selective pressures (reviewed in different chapters of [12, 13, 16] ). In vivo an ''arms race'' is established between the virus and the host: the virus increases its fitness but it must overcome the multiple physiological responses intended to limit virus replication and to clear the virus from the organism. Successful evasion contributes to viral persistence, as documented with different viral pathogens [6, 8, 13, 15, 49] (Tab. I).