Medical characteristics of the orthomyxovirus (flu) family

The name myxovirus was originally applied to influenza viruses. This means a virus with affinity to the mucins. Now there are two main groups - orthomyxoviruses and paramyxoviruses. All orthomyxoviruses are influenza viruses, isolated strains are named after the type of virus (A, B, C), the host and the place of initial isolation, the year of isolation and the antigenic design of hemagglutinin and neuraminidase. Eleven antigenic subtypes of hemagglutinin and 8 antigenic subtypes of neuramidase were prescribed. Both are glycoproteins under separate genetic control, and they change independently of each other. Examples of influenza symbols are: A / swine / New Jersey / 76 (H1N1), formerly (Hsw1N1), A / Brazil / 78 (H1N1), B / Singapore / 79, A / Bangkok / 79 (H3N2).

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Influenza is an infection of the acute respiratory tract that usually occurs during epidemics. Three immunological types of influenza virus are known: A, B and C. Antigenic changes occur constantly in group A of influenza viruses and to a lesser extent in group B, whereas the effect of C is manifested as an antigen. Influenza A strains are also known for pigs, horses, ducks and chickens (bird fever). Some animal isolates are antigenically similar to strains circulating in the human population.

The type of influenza virus type C is different from type A and type B viruses; its receptor-degrading enzyme does not appear to be a neuraminidase, and its structure of the virion is not fully understood. The following descriptions are based on influenza A virus.

Virus properties

Composition

Conformers of influenza virus are pleomorphic, approximately spherical particles with an outer diameter of about 110 nm and an inner electron-dense core of 70 nm. The surface of viral particles is covered with two types of projections or spikes of approximately 10 nm, which possess either hemagglutinin or neuramidase activity of the virus.

Conjugates of the RNA genome of 8 separate parts with a total molecular weight of 2-4 X 10 ^ 6. Because of their divided genome, viruses of this group exhibit some biological phenomena, such as high recombination frequency, multiplication of reactivation, and the ability to synthesize hemagglutinin and neuraminidase after chemical inactivation viral infectivity. Although viral RNA has not proven to be infectious, viral ribonucleoproteins look like this. This structure contains a virion-associated RNA-dependent RNA polymerase, as well as a genome. Apparently, all messianic RNA is complementary to virion RNA.

The results of hybridization studies on RNA confirmed the immunological grouping of hemagglutins of influenza A viruses. Similar studies of the neuramidase genes are consistent with N-antigenic subtype samples based on the results of serological tests.

Reactions of physical and chemical agents

Influenza viruses are stable and can be stored at 0–4 degrees Celsius for several weeks. The virus is less stable at -20 degrees Celsius than at +4 degrees Celsius. Essential and protein denaturing substances destroy infectivity. Hemagglutinin and CF antigens are more stable than the infectious virus. Ultraviolet irradiation destroys infectivity, hemagglutinin activity, neuraminidase activity and CF antigen in that order. Infectivity and hemagglutination are more stable at alkaline pH than at acidic pH.

Susceptibility of animals and growth of the virus

Human virus strains can infect different animals; ferrets are most susceptible to senal passage in mice, increasing its virulence, producing intensive consolidation and death of the lungs. A growing chicken embryo supports the growth of the virus, but there is no serious damage. Wild flu viruses grow poorly in tissue cultures. In most cases, only the abortion growth cycle occurs, i.e., viral subunits are synthesized, but few or no new offspring of infection. From most strains of influenza, mutants can be selected that will grow in cell culture. Due to the poor growth of many strains in cell culture, attempts at initial isolation should apply inoculation to both the amniotic cavity of the embryonic egg and the monkey cell cultures.

The process of infection begins with the adsorption of the virus on its receptor sites (glycoproteins containing neuraminic acid). The gammagglutinin protein is involved in this reaction. Another spike protein, neuraminidase, can destroy the site. The virus particle enters the cell, where it is broken, which leads to a decrease in the detected virus soon after infection with intracellular synthesis of viral RNA and protein. The particles of viral RNA are synthesized individually in the nucleus within 2-3 hours. All viral proteins are synthesized in structural proteins of the cytoplasm, which bind to the cell membrane and are bound by ribonucleoprotein after 8 hours, new virus particles are generated through the membrane. Neuraminidase may be important for the release of a complete virion.

In most influenza systems, non-infectious particles are formed that can agglutinate along the edge. These particles, called "incomplete", increase in quantity with a consistent, highly multiplying passage of the virus. Partial particles are smaller and more pleomorphic than standard viruses, and they interfere with the replication of a standard virus. They are known as defective interfering, or DI, particles, which are the largest part of the RNA virus, are absent in such particles.