Using Altered Fidelity Viruses to Study Viral Attenuation and Population Genetics During Vertebrate Host Infection

The requirement of arthropod and vertebrate hosts for the host life cycle of an arbovirus constrains its evolution. For the viral population to survive in two hosts, the ability to produce genetic diversity within the population is essential. RNA viruses contain an RNA dependent RNA polymerase (RdRp) that creates a population of closely related but slightly different variants following each replication cycle. These variants can interact with each other, allowing the viral population to overcome selection pressures without adapting the consensus sequence to one organism over the other. When the RdRp fidelity is altered, the virus is attenuated in vivo. A potential mechanism for this attenuation could be from the viruses’ inability to overcome bottlenecks during infection. The effects of altered fidelity on mutational coupling and pathogenesis were studied using Venezuelan equine encephalitis virus (VEEV) as a model system. Fidelity mutants were generated and validated in a WT VEEV strain. These mutants were then used to infect mice. Mutants with altered fidelity demonstrated decreased lethality and dissemination compared to the parental virus, suggesting that constraining diversity inhibits a viral population’s ability to recover from bottlenecks occurring during infection.