Viral Genome Evolution

Viral Evolution

• Viruses evolve faster than cells due to their rapid replication and high numbers, allowing for more opportunities for natural selection to fine-tune transmission and infection strategies.
• Reassortment events and random mutations contribute to viral evolution, especially in RNA viruses.

Reassortment Events and Random Mutations

• Genome reassortment occurs when two different viral strains coinfect a single host cell, allowing for the mixing of viral genomes and generation of new viral strains.
• Random mutations also cause viral genomes to change over time, with RNA viruses evolving faster than DNA viruses.
• RNA polymerases lack proofreading capabilities, resulting in higher mutation frequencies (once per round of genome copying) compared to DNA polymerases (once per thousand rounds of genome copying).

Consequences of Mutation

• Mutations can have neutral, beneficial, or negative effects depending on their location in the genome.
• Genetic changes that limit infectivity are unfavorable and result in attenuated strains, which are ideal for vaccine development (e.g., oral polio vaccine).
• Beneficial mutations can allow viruses to escape host immune system detection, broaden host range, expand tropism, or increase infectivity.

Examples of Viral Evolution

• SARS-CoV-2 evolved enhanced infectivity traits, complicating the COVID-19 pandemic.
• Influenza viruses are a classic model for studying the effects of spontaneous mutations and reassortment in viral evolution.