page_title: Virology
section_title: History of virology
hierarchical_section_title: Virology / History of virology
caption_attribution_description: English: Martinus Beijerinck in his laboratory.The photographer is unknown. It's in a professional-style mount, but there's no names embossed on the mount. It has the date 12 May 1921 on the back in his sister's handwriting, so it was taken just before he retired on 21 June 1921, and left Delft for good.
context_page_description: Virology is the study of viruses – submicroscopic, parasitic particles of genetic material contained in a protein coat – and virus-like agents. It focuses on the following aspects of viruses: their structure, classification and evolution, their ways to infect and exploit host cells for reproduction, their interaction with host organism physiology and immunity, the diseases they cause, the techniques to isolate and culture them, and their use in research and therapy. Virology is a subfield of microbiology.
context_section_description: The word virus appeared in 1599 and originally meant "venom".
  A very early form of vaccination known as variolation was developed several thousand years ago in China. It involved the application of materials from smallpox sufferers in order to immunize others. In 1717 Lady Mary Wortley Montagu observed the practice in Istanbul and attempted to popularize it in Britain, but encountered considerable resistance. In 1796 Edward Jenner developed a much safer method, using cowpox to successfully immunize a young boy against smallpox, and this practice was widely adopted. Vaccinations against other viral diseases followed, including the successful rabies vaccination by Louis Pasteur in 1886. The nature of viruses, however, was not clear to these researchers.
  In 1892, the Russian biologist Dmitry Ivanovsky used a Chamberland filter to try to isolate the bacteria that caused  tobacco mosaic disease. His experiments showed that crushed leaf extracts from infected tobacco plants remained infectious after filtration. Ivanovsky reported a minuscule infectious agent or toxin, capable of passing the filter, may be being produced by a bacterium.
  In 1898 Martinus Beijerinck repeated Ivanovski's work but went further and passed the "filterable agent" from plant to plant, found the action undiminished, and concluded it infectious – replicating in the host – and thus not a mere toxin. He called it contagium vivum fluidum. The question of whether the agent was a "living fluid" or a particle was however still open.
  In 1903 it was suggested for the first time that transduction by viruses might cause cancer. In 1908 Bang and Ellerman showed that a filterable virus could transmit chicken leukemia, data largely ignored till the 1930s when leukemia became regarded as cancerous. In 1911 Peyton Rous reported the transmission of chicken sarcoma, a solid tumor, with a virus, and thus Rous became "father of tumor virology". The virus was later called Rous sarcoma virus 1 and understood to be a retrovirus. Several other cancer-causing retroviruses have since been described.
  The existence of viruses that infect bacteria (bacteriophages) was first recognized by Frederick Twort in 1911, and, independently, by Félix d'Herelle in 1917. As bacteria could be grown easily in culture, this led to an explosion of virology research.
  The cause of the devastating Spanish flu pandemic of 1918 was initially unclear. In late 1918, French scientists showed that a "filter-passing virus" could transmit the disease to people and animals, fulfilling Koch's postulates.
  In 1926 it was shown that scarlet fever is caused by a bacterium that is infected by a certain bacteriophage.
  While plant viruses and bacteriophages can be grown comparatively easily, animal viruses normally require a living host animal, which complicates their study immensely. In 1931 it was shown that influenza virus could be grown in fertilized chicken eggs, a method that is still used today to produce vaccines. In 1937, Max Theiler managed to grow the yellow fever virus in chicken eggs and produced a vaccine from an attenuated virus strain; this vaccine saved millions of lives and is still being used today.
  Max Delbrück, an important investigator in the area of bacteriophages, described the basic "life cycle" of a virus in 1937: rather than "growing", a virus particle is assembled from its constituent pieces in one step; eventually it leaves the host cell to infect other cells. The Hershey–Chase experiment in 1952 showed that only DNA and not protein enters a bacterial cell upon infection with bacteriophage T2. Transduction of bacteria by bacteriophages was first described in the same year.
  In 1949 John F. Enders, Thomas Weller and Frederick Robbins reported growth of poliovirus in cultured human embryonal cells, the first significant example of an animal virus grown outside of animals or chicken eggs. This work aided Jonas Salk in deriving a polio vaccine from deactivated polio viruses; this vaccine was shown to be effective in 1955.
  The first virus that could be crystalized and whose structure could, the
caption: Martinus Beijerinck in his laboratory in 1921.
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