History of Virology: Vertebrate Viruses

The word virus originally meant poison, but with Pasteur׳s discoveries it became synonymous with microbe. In the 1890s, the terms filterable or ultramicroscopic viruses were used but by the 1930s these adjectives were dropped. Foot-and-mouth disease virus was discovered in 1898 and yellow fever virus was shown to be an arthropod-borne virus in 1900-01. Between 1940 and the early 1990s it was shown that the genome of viruses could consist of linear double-stranded DNA (dsDNA) or circular partially single-stranded DNA (ssDNA), or negative or positive dsRNA or ssRNA, in one, two, three, or eight fragments. Replication of retroviruses was shown to be due to transcription of the RNA genome into DNA and its integration into cell׳s DNA. In 1930 mice were first used for assaying viruses, followed in 1934 by use of the chorioallantoic membrane of developing chick embryos and in 1952 by plaque assay in cultured cells. Virions come in a variety of forms: roughly spherical, with a lipid coat, isometric icosahedral, oval, and elongated. Some cause tumors, in animals and/or humans. Important events during the 1980s included development of the polymerase chain reaction and the nature and worldwide spread of HIV-AIDS.