Wednesday, September 13, 2017

Virus History

Viruses History

Viruses were discovered at the end of the 19th century. In 1892, Dimitri Ivanovsky, a Rusian botanist, discovered that the sap from tobacco plants affected by mosaic diseases could be passed through filters so fine as to exclude all known bacteria and still retain the ability to produce the diseases in new plants. In 1898, Frederich Loeffler and Paul Frosch reported similar results for the infectious agent of foot-and-mouth diseases of cattle. They also showed that an animal inoculated with a tiny amount of filtered material could itself subsequently give rise to a very potent inoculums. This indicated that the infectious agent was able to reproduce itself within the infected animal. During the next three decades many viruses were discovered. Unlike other microorganisms, none of the viruses could be propagated in the absence of host cells, which led researchers to conclude that viruses are intracellular parasites.

Beginning in the 1930s, a number of new techniques were developed for virology, or the study of viruses. The discovery that many animal viruses can be grown in mice and in chicken embryos allowed the course of viral infection to be studied under controlled laboratory conditions. Very high-speed centrifuges were developed that made possible the preparation highly purified virions. Chemical analysis showed that viruses consist primarily of nucleic acid and protein, and the development of the electron microscope during the 1940s permitted scientists to study the size and shape of these virions in great detail.

Because of the ease with which bacteria can be grown and manipulated in the laboratory, many of the features of intracellular viral development were first discovered by studying bacteriophage, which are viruses that grow in bacteria. During the late 1950s techniques for growing animal cells in tissue culture were developed, making possible the detailed study of the intracellular growth of animal viruses.

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