From Quasispecies Theory to Viral Quasispecies: How Complexity has Permeated Virology

RNA viruses replicate as complex and dynamic mutant distributions. They are termed viral quasispecies, in recognition of the fundamental contribution of quasispecies theory in our understanding of error-prone replicative entities. Viral quasispecies have launched a fertile field of transdiciplinary research, both experimental and theoretical. Here we review the origin and some implications of the quasispecies concept, with emphasis on internal interactions among components of the same mutant virus ensemble, a critical fact to design new antiviral strategies. We make the distinction between intrinsic and extrinsic properties of mutant distributions, and emphasize that there are several levels of complexity that can influence viral quasispecies behavior.