Calicivirus is a highly infectious RNA virus in the family Caliciviridae. It has a small single stranded positive sense RNA genome which indicates that there is a high degree of genomic plasticity. This is shown in its RNA polymerases poor ability to proofread resulting in mutations. This enables the virus to respond rapidly to selections pressures in the environment making it a very adaptable virus. Calicivirus replicates in the oral and respiratory tissues of cats.