Viruses are very tiny organic structures consisting of either DNA or RNA encapsulated within a protein shell called capsid. Since viruses cannot reproduce by themselves because of the simplicity of their components, they must infect other living organisms, utilize the metabolic pathways of the host cell to reproduce viral components, and assemble these components in the cell. Viruses can infect all types of living organisms, from animals and plants to bacteria and archaea, and often lead to serious problems such as diseases and death in their hosts. They are responsible for a variety of infectious diseases including the common cold, infl uenza, Acquired Immune Defi ciency Syndrome (AIDS), and chickenpox. In particular, viral gastrointestinal and respiratory infections cause a considerable health and economic burden in terms of hospitalization, medical costs, doctor’s consultations, and absenteeism from work and school. For instance, rotavirus and norovirus frequently cause group infection, especially inchildren, and patients suffer from diarrhoea, vomiting, and fever. Infl uenza viruses not only lead to a seasonal epidemic annually, but also sometimes to a pandemic, resulting in high morbidity and signifi cant mortality.