Transient evolutionary epidemiology of viral adaptation and lethal mutagenesis

Beneficial mutations drive the within-host adaptation of viral populations and can prolong the duration of host infection. Yet, most mutations are not adaptive and the increase of the mean fitness of viral populations is hampered by deleterious and lethal mutations. Because of this ambivalent role of mutations, it is unclear if a higher mutation rate boosts or slows down viral adaptation. Here we study the interplay between selection, mutation, genetic drift and within-host dynamics of viral populations. We obtain good approximations for the transient evolutionary epidemiology of viral adaptation under the assumption that the mutation rate is high and the effects of non-lethal mutations remain small. We use this theoretical framework to discuss the feasibility of lethal mutagenesis to treat viral infections in the light of quantitative predictions we obtained for the critical mutation rates of a range of different viruses.