Viral Evolution: It Is All About Mutations

Viral infection is a highly dynamic process, which lead to constant evolutionary changes on both sides of the viral–host interface. The high mutation rates of viruses, coupled with short generation times and large population sizes, allow viruses to rapidly adapt to the host environment. However, this high mutation rate also comes at a cost to the viral population, as deleterious mutations are constantly created, leading to a plethora of defective genomes. Here, we will discuss the basic tenets that govern the evolution of viruses: mutation rates, population size, selection, the multiplicity of infection, and how these factors modulate infection as viruses evolve within a host, during transmission to novel susceptible hosts, and as viruses establish infections in new host species.