Villains or heroes? The raison d'être of viruses

Watanabe, Tokiko; Kawaoka, Yoshihiro

Viruses, which consist of nucleic acid encased in a protein shell, are parasites of host organisms. The term 'virus' comes from the Latin word 'venom', which means poison, because a virus is generally considered to be a causative agent like a poison that causes infectious diseases. These tiny, living entities have considerable import, because they can cause substantial damage to humans and non-human animals and other living organisms. The relationship between humankind and viruses has a long history. For example, the earliest evidence of smallpox was found in 3000-year-old Egyptian mummies, who had smallpox-like eruptions on their skins. 1 The overall mortality rate of smallpox was around 30%, 2 making it one of the most feared infectious diseases. In 1918-1919, during World War I, influenza A virus caused the Spanish flu pandemic, resulting in infection of approximately 500 million people and more than 20-40 million death worldwide. 3 Since the initial isolation of viruses in the 19th century, scientists have identified and characterised a wide variety of viruses, and the field of virology has progressed remarkably since then, enabling us to combat the frequently deadly effects of these viruses. One of the greatest achievements is the complete eradication of smallpox. Although smallpox was once rampant in the world, vaccination of the entire population has eradicated this disease. 1 Similarly, the poliovirus vaccine has significantly reduced the incidence of poliomyelitis. 4 Despite the progress of virology, we still have many unconquered viral diseases and we are confronted with the problem of emerging infectious diseases, which are caused by newly identified species or strains. For example, Ebola virus disease and acquired immunodeficiency syndrome emerged in 1976 and 1981, respectively, 5-9 and more recently, severe acute respiratory syndrome (SARS), highly pathogenic avian influenza viruses and Middle East respiratory syndrome (MERS) have appeared in human society. [10] [11] [12] [13] [14] [15] Therefore, it is important to continue studying the mechanisms of viral replication and pathogenicity.