Influenza

A contagious respiratory illness caused by influenza viruses, producing seasonal epidemics nearly every year and, periodically, far more severe pandemics when a novel strain emerges with little population immunity, as in the 1918 to 1919 pandemic, estimated to have killed 50 million people or more worldwide, more than the First World War itself. The name derives from the Italian influenza, reflecting an old belief that outbreaks were under the influence of the stars; the term entered English usage following the widespread 1743 epidemic. The influenza virus itself was not isolated until 1933, by Wilson Smith, Christopher Andrewes and Patrick Laidlaw.