IDENTIFICATION OF VIRUSES

From Big Medical Encyclopedia

IDENTIFICATION OF VIRUSES (late lat. to identify identificare; viruses) — definition of patrimonial and specific accessory of viruses, establishment of their identity or difference by comparison to already known viruses.

And. is the final stage at laboratory diagnosis of viral diseases century; it is widely carried out also at epidemiol, researches and during the work in the field of theoretical virology.

And. it is carried out by studying of their morphology, physical century. - chemical properties, biol, features and an antigenic structure; it will be out on the basis of the existing classification of viruses. At And. century at first define their belonging to a certain classification group. If the group represents family, in addition define a sort of a virus (e.g., accessory of the studied picornavirus to entero-or to rhinoviruses). Further establish a type of a virus, and for the types which are subdivided into types (e.g., viruses of poliomyelitis, flu), also their type.

Group accessory of a virus is caused by a look being its part nucleinic to - you and its pier. the weight, the place of formation (assembly) of a capsid in a cell, number of capsomeres, a type of symmetry of a nucleocapsid, existence or lack of a cover, lipids, the sizes of virion. Practically for And. there is usually enough definition of only several, the most important of the listed indicators century.

After establishment of a sort define a type of a virus (and for certain viruses also type) by studying of its antigenic structure by immune serums to typical representatives of different types (and types) viruses of this sort. Less often with the same purpose use other methods.

The most difficult is And. century which according to the characteristics cannot be carried to one of the existing classification groups. The conclusion is very responsible that the studied virus is other than all known; it can be made only after studying of all complex of its properties.

And. it is, as a rule, carried out after their reproduction century to laboratories therefore for a research bodies of the infected animals, fabrics and liquids of embryos of birds, a medium or cells of the infected cellular and fabric cultures undertake. If the virus does not manage to be cultivated in vitro, then for And. use the material taken directly from the patient or the dead of an organism century.

The sizes of a virus most precisely define with the help submicroscopy (see), edges at the same time gives the chance to receive data on structure of virion. For an elektronnomikroskopichesky research it is necessary to have high cleaning and konts. material. For this purpose it is preferable to use high-speed centrifuging in a gradient of density of sucrose (see. Ultratsentrifugirovaniye ), what allows not only to clear a virus of ballast substances, but in the presence in material of several viruses and to divide them if they differ in size.

At some viral infections for the purpose of bystry diagnosis of an elektronnoskopicheska investigate the material taken without pretreatment directly from the patient (e.g., contents of pustules for differentiation of smallpox and chicken pox). This method finds more and more broad application at diagnosis of viral infections.

Size discrimination of viruses by means of filtering via cellulose membrane filters (see. Ultrafiltration, in virology ) is less exact. It is necessary to have a set of filters with various diameter of a time. Further for each filter the correction factor of adsorption showing a ratio between diameter of a time and the maximum size of virions which can pass through them shall be defined. For this purpose the filter is calibrated, using particles of the known size. The studied material shall be exempted from rough particles by a transmission via the sterilizing filter or centrifuging within 10 — 15 min. at a speed of 2000 — 3000 rpm. For reduction of adsorption of a virus previously filter any kapillyarnoaktivny substance (broth, solution of peptone, etc.) or it is added to a virus suspension. Filtering of material is carried out consistently, since the most krupnoporisty filter. The size of a virus is received by multiplication of size of a time of the membrane partially detaining him by coefficient of adsorption for the filter of this porosity.

For definition of type being a part of a virus nucleinic to - you it is allocated by processing of a virus suspension with water-saturated phenol, anionic detergents, napr, dodetsilsulfaty sodium and others, with the subsequent chemical analysis. If the virus breeds in cultures of cells, type nucleinic to - you often determine by an indirect method which is based on ability halide derivative a dezoksiuridina, in particular 5-bromine-2-dezoksiuridina, to selectively suppress reproduction of the DNA-containing viruses and not to influence a reproduction of the majority of RNA-containing. Drug bring in a medium in a dose from 40 to 100 mkg/ml at infection of cellular culture with a virus.

Indicative data on type nucleinic to - you viruses can be obtained on coloring of the infected cells of a flyuorokhromama, napr, acridine orange (it is used in cultivation 1:10000 — 1:20000 in isotonic solution of sodium chloride with the phosphatic pH 7,2 — 7,4 buffer). At connection with RNA acridine orange fluoresces red, and after reaction with DNA — green. This method allows to define type nucleinic to - you virus components in places of their accumulations in cells. The method of differential diagnosis of a number of respiratory infections is based on it: do a smear print from the lower nasal sink of the patient; after coloring by acridine orange intracellular inclusions of influenza viruses and a parainfluenza begin to shine red, and at an adenoviral infection and herpes — green.

Existence or absence in a cover of viruses of lipids establish on sensitivity to effect of solvents of lipids, napr, ether. The virus suspension is connected to the equal volume of ether, stirred up within 20 min. at the room temperature, then maintain 18 — 20 hours at t ° 4 ° in densely closed ware. Further test is poured in a Petri dish and maintained for evaporation of ether of 30 min. at t ° 36 — 37 ° then it is titrated in parallel with the raw material for determination of quantity of a virus. In the presence in a viral envelope of lipids it at influence of ether is inactivated.

Carrying out these researches usually allows to carry the studied strain to a certain classification group or to number of not classified viruses. Further And. carry out in group by their comparison to typical representatives of separate types century. In some cases researches in group can be limited. So, viruses of family of a pikorn are tested for stability in acid medium. Rhinoviruses at pH 3,0 — 5,3 during 1 — 3 hour are inactivated while enteroviruses keep the infectivity.

And. century with the help serol, reactions carry out by their testing with serums to the known viruses or, on the contrary, test the immune serums prepared for the studied strains with the known viruses.

Serol, identification is quite often carried out in two stages. At first the virus is studied in reactions of binding complement (see), or if it has the hemagglutinating activity, in reaction of braking hemagglutinations (see), and then by means of a neutralization test. RSK concerning many viruses is not strictly specific. So, adenoviruses of the person and the majority of animals have the general complement-linked antigen. All known reoviruses have the general antigen. Concerning other viruses, napr, influenza viruses, RSK is more specific and allows to define their standard accessory. The same treats RTGA: it allows to define type of a reovirus and is very specific concerning influenza viruses, but at the same time gives group reactions at identification of togavirus.

The most specific is the neutralization test: in most cases she allows to establish both specific, and standard accessory of a virus (for the types which are subdivided into types). It is carried out in various ways. Most often prepare mix of a virus with serum, to-ruyu then test one way or another for existence of not neutralized virus.

Much more rare And. carry out by cross testing of immunity century: animals are immunized an unknown virus, and then infected known or on the contrary.

Very widely for And. use century immunofluorescence (see). Most often the cellular cultures infected with an unknown virus investigate with fluorescent immunoglobulin to the known virus. Investigate thus material from patients less often (smears from a throat at flu, a brain of patients with a subacute sclerosing panencephalitis on clumsy antigen, a brain of the dead from rage).

Precipitation in an agar is used for And. it is quite rare century. In material from skin defeats of patients with smallpox by this method it is possible to find a viral antigen.

Some types of viruses pe manage to be differentiated rather accurately by studying of their antigenic structure. In such cases resort to additional tests — define pathogenicity for animals, reproduction in various cellular cultures, etc. Thus, e.g., identify viruses of smallpox group. The causative agent of natural smallpox does not cause damages on the scarified leather of a rabbit and does not breed in cultures of cells at t ° higher than 38,5 °. At the same time viruses of a variolovaccine and smallpox of cows cause changes on leather of a rabbit and breed at t ° to 40 °. Viruses also on morphology of defeats on a horionallantoisny cover of a chicken embryo differ.

Sometimes there is a need of differentiation of vaccinal strains of viruses from «wild». So, the fixed rhabdovirus is distinguished from «street» on its inability to cause formation of little bodies of Babesh — Negri in a brain of the infected mice and to some other indicators, vaccinal virus strains of poliomyelitis — on inability to a reproduction at an elevated temperature.

See also Virologic researches .



Bibliography: Gaydamovich S. Ya. Classification and identification of an arbovirus, Vestn. USSR Academy of Medical Sciences, No., page 25, 1972; Laboratory diagnosis of viral and rickettsial diseases, under the editorship of E. Lennet and N. Schmidt, the lane with English, M., 1974; Luriya S. and Darnell Dzh. The general virology, the lane with English, M., 1970; M. I. Falcons, With and N and c to and y A. A. and P I eat e z about in P. I. Virologic and serological researches at viral infections, L., 1972.

E. R. Peele.

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