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virology,study of viruses and their role in disease. Many viruses, such as animal RNA viruses and viruses that infect bacteria, or bacteriophagesbacteriophage
, virus that infects bacteria and sometimes destroys them by lysis, or dissolution of the cell. Bacteriophages, or phages, have a head composed of protein, an inner core of nucleic acid—either deoxyribonucleic acid (DNA) or ribonucleic acid (RNA)—and a
..... Click the link for more information. , have become useful laboratory tools in genetic studies and in work on the cellular metabolic control of gene expression (see nucleic acidsnucleic acid,
any of a group of organic substances found in the chromosomes of living cells and viruses that play a central role in the storage and replication of hereditary information and in the expression of this information through protein synthesis.
..... Click the link for more information. ). Because viruses can sometimes carry extra genetic material into host cells, they have been used to experimentally transfer genetic material, specifying a particular enzyme, into nuclei of mammalian host cells that lacked the ability to synthesize that enzyme. The ability of viruses to transfer genetic material has also been extensively studied in bacteria (see recombinationrecombination,
process of "shuffling" of genes by which new combinations can be generated. In recombination through sexual reproduction, the offspring's complete set of genes differs from that of either parent, being rather a combination of genes from both parents.
..... Click the link for more information. ). Virus-mediated gene transfers are medically interesting because of the possibility that in the future enzyme-specifying genes might be transferred into humans with hereditary enzyme-deficiency diseases. Virus interference is a phenomenon in which host cells, while infected by one virus, are protected against infection by other viruses; the technique has been used experimentally as a form of temporary immunization. Interferon, a vast number of proteins produced by virus-infected cells that inhibits viral replication within the cell has been studied with a view toward preventing or controlling virus-caused diseases. Viruses continue to be investigated because they are held to be possible causative agents of some human cancers, and because under certain conditions the body's immune response to virus infection may cause tissue damage and develop into an autoimmune disease. Viruses can have high rates of mutations (point mutations) that keep them undetectable. Human immunodeficiency virus (HIV), the virus associated with AIDS, is a retrovirus that appears to have mutated into a number of strains that attack the immune system and produce viral-induced immunosuppression.
inframicrobiology, the science of viruses— submicroscopic intracellular parasites. Only in the middle of the 20th century did virology become an independent discipline. Initially the virology of humans, animals, and bacteria developed within the framework of microbiology, whereas the virology of higher plants was a division of phytopathology. Virology occupies an important position among the biomedical sciences because virus diseases are widespread in humans, animals, and plants. Moreover, viruses serve as models on which the fundamental problems of genetics and molecular biology are studied. The first monographs on viral diseases in animals were published by T. M. Rivers (London, 1928) and N. F. Gamaleia (Moscow, 1930), whereas the earliest works on viral diseases in plants were by V. L. Ryzhkov (Moscow, 1933) and K. Smith (London, 1933). The first laboratory (for viral plant diseases) was set up in 1930 at the Ukrainian Institute of Plant Protection. In 1932 laboratories for viral diseases in man appeared at a number of institutes of medical microbiology. The D. I. Ivanovskii Institute of Virology has been in existence in Moscow since 1946. The first conference on viral plant diseases was held in March 1935 in Kharkov, and the first conference on ultramicrobes, filterable viruses, and bacteriophages was held in December of the same year in Moscow. In 1966 at the ninth International Congress of Microbiology the International Committee on the Nomenclature of Viruses was set up for the first time. In 1968 the First International Congress on Viruses was held in Helsinki.
In a methodological sense, virology differs fundamentally from microbiology, since viruses cannot be cultivated in artificial nutrient media. For experiments with viruses it is necessary to use plants and animals that are sensitive to them, chick embryos (1932), and isolated tissues (since 1913 and particularly since 1925). The progress of virology de-pended above all on developing a convenient method of cultivating viruses. Thus, the study of the flu virus advanced when it was determined that polecats (1933) and white mice (1934) are sensitive to this virus. In the study of poliomyelitis and measles viruses and also in creating preventive vaccines against these diseases the cultivation of viruses in isolated monkey and human tissues was crucially important. Different methods of titration are used for quantitative consideration of the virus and the dynamics of its reproduction. The most important methods are based on the fact that the virus, when multiplying in the cell, causes lesions visible to the naked eye. Bacterial viruses (bacteriophages) are titrated by the number of sterile spots (F. d’Herelle, 1917); plant viruses are titrated by the number of necroses on the leaf infected by the virus (F. Holmes, 1929); human and animal viruses are titrated on monolayer tissue cultures (R. Dulbecco, 1952). The virus of mosaic disease of tobacco was first separated by chemical means by W. Stanley (1935). Development of the ultracentrifuge made it easier to concentrate viruses and determine the mass of virus particles. So-called gradient or fractionated centrifuging in solutions of saccharoses or metal salts made it possible to “sort out” the virus particles, since, even though the difference in their weight is insignificant, they are distributed in layers at different levels of the solution. This method played an important part in the study of the stages of virus reproduction. For studying the physiological conditions of virus reproduction, V. L. Ryzhkov (1938) proposed the method of metabolites and antimetabolites. This method began to be used for determining the influence on virus reproduction of substances that stimulate or inhibit particular biochemical processes. The use of isotopes (primarily radioactive) made it possible to trace the sources from which the virus takes substances for its growth. Particular stages in virus reproduction are studied in noncellular preparations, which contain, in addition to the virus, ribosomes, cell enzymes, and substances needed for building proteins and nucleic acids. Since 1938 electron microscopy has made it possible to see virus particles, and since 1945 the possibility of preparing ultrafine microscopic sections has furthered the study of the development of the virus in tissues.
Virology is closely related to cell morphology and physiology since the cell is the dwelling place of viruses. On the other hand, the dimensions of virus particles are close to the dimensions of large molecules, and this makes it possible to study them using methods applied in the study of molecules (roentgen structural analysis and so on). The main problems of modern virology are the classification of viruses, chemotherapy for virus diseases, and questions related to genetics and molecular biology.
Journals on virology include Voprosy virusologii (Moscow, 1956—), Archiv für die gesamte Virusforschung (Vienna, 1939—), Virus (Kyoto, 1951—), Virology (New York, 1955—), Acta virologica (Prague, 1957—), Journal of General Virology (London, 1967—), and Journal of Virology (Baltimore, 1967—).
REFERENCESRyzhkov, V. L. “Kratkii ocherk istorii izucheniia virusov.” Tr. Instituta istorii estestvoznaniia i tekhniki AN SSSR, 1961, vol. 36, no. 8.
Aktual’nye voprosy virusologii. Moscow, 1965.
Molekuliarnye osnovy biologii virusov. Moscow, 1966.
Zhdanov, V. M., and S. la. Gaidamovich. Virusologiia. Moscow, 1966.
Ryzhkov, V. L. “Virusologiia.” In the collection Razvitie biologii v SSSR. Moscow, 1967.
Virusnye bolezni rastenii: Bibliografiia otechestvennoi literatury za 1924-1966. Moscow, 1967.
V. L. RYZHKOV