page_title: History of virology
section_title: Influenza
hierarchical_section_title: History of virology / 20th century / Influenza
caption_attribution_description: Typist wearing mask, New York City, October 16, 1918, during the "Spanish flu" influenza pandemic. The flu prevented day-to-day operations from going smoothly. Officials advised all persons to wear face masks, even indoors. Many believed that a person could contract the disease by handling documents and equipment. Record held at: National Archives at College Park, MD. Record number 165-WW-269B-16.
context_page_description: The history of virology – the scientific study of viruses and the infections they cause – began in the closing years of the 19th century. Although Louis Pasteur and Edward Jenner developed the first vaccines to protect against viral infections, they did not know that viruses existed. The first evidence of the existence of viruses came from experiments with filters that had pores small enough to retain bacteria. In 1892, Dmitri Ivanovsky used one of these filters to show that sap from a diseased tobacco plant remained infectious to healthy tobacco plants despite having been filtered. Martinus Beijerinck called the filtered, infectious substance a "virus" and this discovery is considered to be the beginning of virology.
  The subsequent discovery and partial characterization of bacteriophages by Frederick Twort and Félix d'Herelle further catalyzed the field, and by the early 20th century many viruses had been discovered. In 1926, Thomas Milton Rivers defined viruses as obligate parasites. Viruses were demonstrated to be particles, rather than a fluid, by Wendell Meredith Stanley, and the invention of the electron microscope in 1931 allowed their complex structures to be visualised.
context_section_description: Although the influenza virus that caused the 1918–1919 influenza pandemic was not discovered until the 1930s, the descriptions of the disease and subsequent research has proved it was to blame.
  The pandemic killed 40–50 million people in less than a year, but the proof that it was caused by a virus was not obtained until 1933. Haemophilus influenzae is an opportunistic bacterium which commonly follows influenza infections; this led the eminent German bacteriologist Richard Pfeiffer (1858–1945) to incorrectly conclude that this bacterium was the cause of influenza. A major breakthrough came in 1931, when the American pathologist Ernest William Goodpasture grew influenza and several other viruses in fertilised chickens' eggs. Hirst identified an enzymic activity associated with the virus particle, later characterised as the neuraminidase, the first demonstration that viruses could contain enzymes. Frank Macfarlane Burnet showed in the early 1950s that the virus recombines at high frequencies, and Hirst later deduced that it has a segmented genome.
caption: A woman working during the 1918–1919 influenza epidemic. The face mask probably afforded minimal protection.
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