From Big Medical Encyclopedia

PERSISTENTION OF VIRUSES (Latin persistere to remain, to persist; viruses) — long preservation of a virus in an organism of the owner or in cellular culture.

At an acute inf. diseases time of stay of a virus in an organism is defined by duration of an incubation interval and the period uncomplicated a wedge, diseases. Preservation of a virus longer than this term represents P. century; in some cases P. lasts century for months and years, sometimes all life.

The term «persistention» is offered in 1923 to K. Levaditi and Sh. Nikolau. Persistention of viruses, including bacteriophages in bacteria, was for the first time described in 1921 by Zh. Borde and Chuke (M. Ciuca); later (in 1950). A. Lvov and A. Gutmann showed that the persistent bacteriophage exists in bacteria in the form of a noninfectious prophase which activation causes a lysis of bacteria (see. Lysogeny ).

Depending on existence or lack of external manifestations of a phenomenon of a persistention of pathogenic or potentially pathogenic viruses distinguish: latent viral infections (see) with periodic aggravations (or without them), in intervals between them the virus is not found; persistent viral infections with constantly allocated virus, more or less expressed symptoms of a disease of an organism (or defeats of cells); slow viral infections (see), characterized long, sometimes by a long-term incubation interval with the subsequent steady development of the disease leading to death of an organism. A number of researchers includes group of the persistent viral infections proceeding asymptomatically, which are not followed by constant allocation to the environment of a virus in this classification. Items of century, proceeding without symptoms or with a little expressed signs of defeat, call also a carriage of virus (see. Carriage of contagiums ). In 1963 W. Smith allocated as a special form P. of century virus symbiosis — the association of a nonpathogenic virus with cells of the owner representing mutual benefit for this purpose and another; existence of this form P. of century admits not all. Borders between different manifestations of a phenomenon of P. of century are considerably conditional.

P.'s definition century and a research of mechanisms of a persistention are a basis for studying of an etiology and a pathogeny of a number of viral diseases that allows to develop effective measures of their prevention and treatment. The item in: can play a role in formation of immunity of an organism to a viral infection for the account interferences of viruses (see), products interferon (see) and antibodies (see), increases in nonspecific resistance of an organism (activation of phagocytosis, specific sensitization of an organism). Special epidemiol, danger is constituted by persistent viral infections at which to the environment the virus is allocated. At the same time P. century is of great importance in ecology of activators since promotes preservation of a virus as a look.

The item of century depends on degree resistance of an organism (see) or the cultivated cells: the organism is less susceptible to this virus, the latent forms of an infection are observed more often. Relative stability of an organism (or cells) to some viruses can be caused genetic and immunol, factors. An important role is played at the same time immunol, by tolerance, an immunodepressive effect of viruses, formation of cell-bound immune complexes in which antibodies neutralize activity of a virus, existence of immunodeficiencies, suppression of production of interferon and disappearance from a surface of the infected cells of virus determinants under the influence of antibodies. P. is frequent century the selection of insensitive cells happening during a viral infection from the general cell population promotes. In the course of P. century of property of virus population can also change: decrease in degree of virulence, loss of the hemagglutinating activity, change of morphology, and sometimes and an antigenic structure of virions is possible.

As a result of change of reactivity of cells and properties of viruses a wedge, P.'s manifestations can significantly differ from symptoms of the acute infection caused by the same virus century.

Studying of mechanisms P. of century at the level of a macroorganism is connected with great difficulties therefore the main data are received on model systems in cultures of cells of the person and animals. Depending on sensitivity of cells, from properties of viruses and from conditions of statement of experiences various reactions of cells to infection with viruses are observed: from an acute infection with total destruction of cells to P. century with a little expressed cytopathic effect or its absence with sharp activation of cellular division — tsitoproli-ferativny effect (see. Cell, virus cytopathology ).

On cellular cultures it was revealed that P. in some cases is connected century with formation of the defective interfering particles («an incomplete virus») which do not have infectivity, but capable to interfere with standard («full») virions. In this case synthesis of standard and defective virions in a cell can be in such balance that the infection will proceed in a subacute or latent form. One of widespread

mechanisms P. of century — integration of a virus genome with cellular in uniform genetic structure. This phenomenon which is result of the recombinational mechanism was for the first time found during the studying of the vzaimodey-Viy of bacteria with moderate phages. Presence at zooblasts of a number of DNA-containing of oncogenous viruses, and also some adenoviruses and a virus of usual herpes was established. The RNA-containing Oncogenous viruses of animals by means of enzyme — the return transcriptase (revertaza) form the DNA transcripts integrating with a cellular genome. V. M. Zhdanov assumed that one of possible mechanisms of a long persistention in cells of not oncogenous RNA-containing of viruses is formation of DNA transcripts by means of a revertaza of an oncogenous virus, latentno pe rehearsing in the same cell.

As a rule, at P. century in cellular cultures the virus is present only at separate cells. Periodic death of the infected cells and reproduction of the cells which kept viability cause change of cycles of destruction of chronically infected cultures by cycles of a repopulyation, i.e. recovery of a cellular layer. Century in population can vary quantity of the infected cells at P. depending on intensity of a producing interferon in cell population, and also from ability of a virus to be transferred in this culture from a cell to a cell, passing an exit in culture medium, from addition on Wednesday of specific antibodies, interferon or inhibitors. In general the lowered products of a virus are, as a rule, characteristic of P. century in cellular cultures unlike an acute infection.

P.'s establishment often presents century considerable difficulties, especially at latent infection. Besides, P.'s identification is at a loss in connection with an originality a wedge, P.'s manifestations century, especially at slow viral infections, change biol, properties of a virus in the course of a persistention century, and also masking of a virus specific antibodies.

For allocation of a persistent virus sensitive test objects infect with the examinee material in the form of cellular homogenates or a suspension of not destroyed cells. As test objects use animals, sensitive to a virus, and also cellular and organ cultures. Sometimes the demaskirovka of a persistent virus is reached by repeated browning of the examinee of material on sensitive organisms or cellular cultures (a method of «blind» passages). Apparently, in the course of repeated browning there is not only an accumulation of virions, but also reduction of fraction of defective interfering particles in virus population. Enrichment of material standard virions can also be reached by preparative centrifuging, concentration of the examinee of material by means of the phase systems formed by water solutions of polymers or by means of precipitation of virions from suspension addition of the nitrogen-containing bases at certain pH values. In some cases for allocation of a virus use a phenomenon of transfection: enter into sensitive test objects allocated from the examinee of material DNA or RNA and in the presence in material infectious nucleinic to - you a virus occur it replication (see).

One of the most effective methods lab. P.'s diagnoses century — activation of a persistent virus, i.e. the sharp strengthening of its reproduction which is followed by recovery of infectious and antigenic properties of a virus. Often activation of viruses is observed during the obtaining single-layer cellular cultures from fragments of externally healthy bodies. By this way, e.g., it was established that apprx. 30% of almonds and adenoides removed at children aged up to 10 years are infected with adenoviruses, nothing showing the presence at an organism. It is also possible to activate the virus by means of a method geterokario-is new, i.e. by artificially caused merge jointly the cultivated cells. In this case at merge of cells virus carriers to the indicator cells sensitive to this virus, «the acute infection» of cultures with formation of a virus available to indication by usual virologic and serological methods quite often develops. Activation of a persistent virus as a result of influence physical (a radiant energy, temperature), chemical (inhibitors of synthesis of cellular macromolecules, biogenic amines) or biological (an immunosuppression, consecutive infection the vi-fair-haired-assistant) factors is sometimes possible. Perhaps also creation of an immunological havoc by introduction to an organism of the owner or in the vitro system of allogenic antigens (cells, blood serum).

Serves as an important method of indication of P. of century submicroscopy (see), allowing to find regarding cells not only standard virions, but also a number of subvirus structures. Indirect instructions on P. can be received century also by means of cytologic, cytogenetic and cytochemical methods of a research.

Apply a method of fluorescent antibodies to identification of antigens of persistent viruses (see. Immunofluorescence ) and the immunoenzymatic method based on a tag of antibodies or antigens by peroxidase which localization in a cell is defined by tsitokhimichesk. Presence at a cell of the virusospetsifichesky sequences of nucleotides at the integration mechanism P. of century is found by method of molecular hybridization of the purified cellular DNA with nucleinic to - that a virus. Besides, for the purpose of P.'s indication use century ability of persistent viruses to interfere with indicator viruses, a phenomenon of long preservation of IgM-antibodies in blood serum at P. century, etc.

See also Viruses .

Bibliography: A. F. coopers and Bocharov of E. F. Persistention of viruses, Novosibirsk, 1979; Gavrilov V. I., Semenov B. F. and Zhdanov B. M. Persistent viral infections and their modeling, M., 1974; Zuev V. A. Laboratory diagnosis of latent, persistent and slow viral infections, M., 1979; V. D.'s Nightingales, X e with both Ya. E N, and B y to about in with to and y A. F. Sketches on virus cytopathology, M., 1979; T and m and to about in EL and 3 at e in V. A. Slow infections, M., 1977; H about t-ch i n J. Persistent and slow virus infections, Basel a. o., 1971.

I. E. Hesinonim