Viruses are subcellular infectious biological agents that rely on the host cell to replicate and complete their life cycle. On their own, viruses lack the complete machinery and energy necessary for their propagation. Viral propagation requires the transcription of viral mRNA, translation of viral proteins, and viral genome replication . The dependence on the host cell to accomplish these processes varies among viruses and largely relates to the nature (DNA or RNA) and the complexity of their genomes. Viruses generally rely less on host functions when their genomes encode one or more of the enzymes required for sustaining virus replication in the cell, such as the viral polymerases and viral proteases .