Abstract: Virology is the science of viruses, microscopic supramolecular creatures of nature, which are a kind of parasitic life form. Virology Virology is a branch of biology that studies viruses.

History of virology, nature and origin of viruses

Virus discovery

Virology is a young science, its history goes back a little over 100 years. Having begun its journey as the science of viruses that cause diseases in humans, animals and plants, virology is currently developing in the direction of studying the basic laws of modern biology at the molecular level, based on the fact that viruses are part of the biosphere and an important factor in the evolution of the organic world.

The history of virology is unusual in that one of its subjects - viral diseases - began to be studied long before viruses themselves were discovered. The beginning of the history of virology is the fight against infectious diseases and only subsequently the gradual disclosure of the sources of these diseases. This is confirmed by the work of Edward Jenner (1749-1823) on the prevention of smallpox and the work of Louis Pasteur (1822-1895) with the causative agent of rabies.

Since time immemorial, smallpox has been the scourge of humanity, claiming thousands of lives. Descriptions of smallpox infection are found in the manuscripts of ancient Chinese and Indian texts. The first mention of smallpox epidemics on the European continent dates back to the 6th century AD (an epidemic among the soldiers of the Ethiopian army besieging Mecca), after which there was an inexplicable period of time when there were no mentions of smallpox epidemics. Smallpox began to spread across continents again in the 17th century. For example, in North America (1617-1619) in the state of Massachusetts, 9/10 of the population died, in Iceland (1707) after a smallpox epidemic, only 17 thousand remained from 57 thousand people, in the city of Eastham (1763) ) from 1331 inhabitants there are 4 people left. In this regard, the problem of combating smallpox was very acute.

A technique for preventing smallpox through vaccination, called variolation, has been known since ancient times. Mentions of the use of variolation in Europe date back to the mid-17th century, with references to earlier experience in China, the Far East, and Turkey. The essence of variolation was that the contents of pustules from patients suffering from a mild form of smallpox were introduced into a small wound on the human skin, which caused a mild disease and prevented an acute form. However, there remained a high risk of contracting a severe form of smallpox and the mortality rate among those vaccinated reached 10%. Jenner revolutionized smallpox prevention. He was the first to notice that people who had cowpox, which was mild, never subsequently suffered from smallpox. On May 14, 1796, Jenner introduced liquid from the pustules of milkmaid Sarah Selmes, who had cowpox, into the wound of James Phipps, who had never suffered from smallpox. At the site of the artificial infection, the boy developed typical pustules, which disappeared after 14 days. Then Jenner introduced highly infectious material from the pustules of a smallpox patient into the boy’s wound. The boy did not get sick. This is how the idea of ​​vaccination was born and confirmed (from the Latin word vacca - cow). In Jenner's time, vaccination was understood as the introduction of infectious cowpox material into the human body in order to prevent smallpox. The term vaccine was applied to a substance that protected against smallpox. Since 1840, smallpox vaccine began to be obtained by infecting calves. The human smallpox virus was discovered only in 1904. Thus, smallpox is the first infection against which a vaccine was used, i.e., the first vaccine-preventable infection. Advances in vaccine prevention of smallpox have led to its worldwide eradication.

Nowadays, vaccination and vaccine are used as general terms denoting vaccination and vaccination material.

Pasteur, who essentially did not know anything specific about the causes of rabies, except for the indisputable fact of its infectious nature, used the principle of weakening (attenuation) of the pathogen. In order to weaken the pathogenic properties of the rabies pathogen, a rabbit was used, into whose brain the brain tissue of a dog that died of rabies was injected. After the death of the rabbit, its brain tissue was injected into the next rabbit, and so on. About 100 passages were carried out before the pathogen adapted to the rabbit's brain tissue. When injected subcutaneously into the dog's body, it exhibited only moderate pathogenic properties. Pasteur called such a “re-educated” pathogen “fixed”, in contrast to the “wild” one, which is characterized by high pathogenicity. Pasteur later developed a method of creating immunity, consisting of a series of injections with gradually increasing amounts of a fixed pathogen. The dog that completed the full course of injections turned out to be completely resistant to infection. Pasteur came to the conclusion that the process of development of an infectious disease is essentially a struggle between microbes and the body's defenses. “Every disease must have its own pathogen, and we must promote the development of immunity to this disease in the patient’s body,” said Pasteur. Not yet understanding how the body produces immunity, Pasteur was able to use its principles and direct the mechanisms of this process to the benefit of humans. In July 1885, Pasteur had the opportunity to test the properties of a “fixed” rabies pathogen on a child bitten by a rabid dog. The boy was given a series of injections of an increasingly toxic substance, with the last injection containing a completely pathogenic form of the pathogen. The boy remained healthy. The rabies virus was discovered by Remlanger in 1903.

It should be noted that neither the smallpox virus nor the rabies virus were the first viruses discovered to infect animals and humans. The first place rightfully belongs to the foot-and-mouth disease virus, discovered by Leffler and Frosch in 1898. These researchers, using multiple dilutions of the filterable agent, showed its toxicity and made a conclusion about its corpuscular nature.

By the end of the 19th century, it became clear that a number of human diseases, such as rabies, smallpox, influenza, and yellow fever, are infectious, but their causative agents were not detected by bacteriological methods. Thanks to the work of Robert Koch (1843-1910), who pioneered the use of pure bacterial culture techniques, it became possible to distinguish between bacterial and non-bacterial diseases. In 1890, at the X Congress of Hygienists, Koch was forced to declare that “... with the diseases listed, we are not dealing with bacteria, but with organized pathogens that belong to a completely different group of microorganisms.” This statement by Koch indicates that the discovery of viruses was not a random event. Not only the experience of working with pathogens that were incomprehensible in nature, but also an understanding of the essence of what was happening contributed to the formulation of the idea of ​​the existence of an original group of pathogens of infectious diseases of a non-bacterial nature. It remained to experimentally prove its existence.

The first experimental evidence of the existence of a new group of pathogens of infectious diseases was obtained by our compatriot - plant physiologist Dmitry Iosifovich Ivanovsky (1864-1920) while studying mosaic diseases of tobacco. This is not surprising, since infectious diseases of an epidemic nature were often observed in plants. Back in 1883-84. The Dutch botanist and geneticist de Vries observed an epidemic of greening of flowers and suggested the infectious nature of the disease. In 1886, the German scientist Mayer, working in Holland, showed that the sap of plants suffering from mosaic disease, when inoculated, causes the same disease in plants. Mayer was sure that the culprit of the disease was a microorganism, and searched for it without success. In the 19th century, tobacco diseases caused enormous harm to agriculture in our country. In this regard, a group of researchers was sent to Ukraine to study tobacco diseases, which, as a student at St. Petersburg University, included D.I. Ivanovsky. As a result of studying the disease described in 1886 by Mayer as mosaic disease of tobacco, D.I. Ivanovsky and V.V. Polovtsev came to the conclusion that it represents two different diseases. One of them - "grouse" - is caused by a fungus, and the other is of unknown origin. The study of tobacco mosaic disease was continued by Ivanovsky at the Nikitsky Botanical Garden under the leadership of Academician A.S. Famytsina. Using the juice of a diseased tobacco leaf, filtered through a Chamberlant candle, which retains the smallest bacteria, Ivanovsky caused a disease of tobacco leaves. Cultivation of the infected juice on artificial nutrient media did not produce results and Ivanovsky comes to the conclusion that the causative agent of the disease is of an unusual nature - it is filtered through bacterial filters and is not able to grow on artificial nutrient media. Warming the juice at a temperature from 60 °C to 70 °C deprived it of infectivity, which indicated the living nature of the pathogen. Ivanovsky first named the new type of pathogen “filterable bacteria” (Figure 1). Results of the work of D.I. Ivanovsky were used as the basis for his dissertation, presented in 1888, and published in the book “On Two Diseases of Tobacco” in 1892. This year is considered the year of the discovery of viruses.

A – Electron micrograph after oblique deposition with carbon and platinum; 65,000´. (Photo by N. Frank.) B – Model. (Karlson, Kurzes Lehrbuch der Biochemie, Stuttgart, Thieme, 1980).

Figure 1 – Tobacco mosaic virus

For a certain period of time, in foreign publications, the discovery of viruses was associated with the name of the Dutch scientist Beijerinck (1851-1931), who also studied tobacco mosaic disease and published his experiments in 1898. Beijerinck placed the filtered juice of an infected plant on the surface of an agar, incubated and obtained bacterial colonies on its surface. After this, the top layer of agar with bacterial colonies was removed, and the inner layer was used to infect a healthy plant. The plant is sick. From this, Beijerinck concluded that the cause of the disease was not bacteria, but some liquid substance that could penetrate inside the agar, and called the pathogen “liquid living contagion.” Due to the fact that Ivanovsky only described his experiments in detail, but did not pay due attention to the nonbacterial nature of the pathogen, a misunderstanding of the situation arose. Ivanovsky’s work became famous only after Beijerinck repeated and expanded his experiments and emphasized that Ivanovsky was the first to prove the non-bacterial nature of the causative agent of the most typical viral disease of tobacco. Beijerinck himself recognized the primacy of Ivanovsky and the current priority of the discovery of viruses by D.I. Ivanovsky is recognized throughout the world.

Word VIRUS means poison. This term was also used by Pasteur to denote an infectious principle. It should be noted that at the beginning of the 19th century, all pathogenic agents were called the word virus. Only after the nature of bacteria, poisons and toxins became clear, the terms “ultravirus” and then simply “virus” began to mean “a new type of filterable pathogen.” The term “virus” took root widely in the 30s of our century.

It is now clear that viruses are characterized by ubiquity, that is, ubiquity of distribution. Viruses infect representatives of all living kingdoms: humans, vertebrates and invertebrates, plants, fungi, bacteria.

The first report related to bacterial viruses was made by Hankin in 1896. In the Chronicle of the Pasteur Institute, he stated that “... the water of some rivers of India has a bactericidal effect...”, which is no doubt related to bacterial viruses. In 1915, Twort in London, while studying the causes of lysis of bacterial colonies, described the principle of transmission of “lysis” to new cultures over a series of generations. His work, as often happens, was virtually unnoticed, and two years later, in 1917, the Canadian de Hérelle rediscovered the phenomenon of bacterial lysis associated with a filtering agent. He called this agent a bacteriophage. De Herelle assumed that there was only one bacteriophage. However, research by Barnett, who worked in Melbourne in 1924-34, showed a wide variety of bacterial viruses in physical and biological properties. The discovery of the diversity of bacteriophages has generated great scientific interest. At the end of the 30s, three researchers - physicist Delbrück, bacteriologists Luria and Hershey, working in the USA, created the so-called “Phage Group”, whose research in the field of bacteriophage genetics ultimately led to the birth of a new science - molecular biology.

The study of insect viruses has lagged significantly behind the virology of vertebrates and humans. It is now clear that viruses that infect insects can be divided into 3 groups: insect viruses themselves, animal and human viruses for which insects are intermediate hosts, and plant viruses that also infect insects.

The first insect virus to be identified was the silkworm jaundice virus (silkworm polyhedrosis virus, called Bollea stilpotiae). As early as 1907, Provacek showed that a filtered homogenate of diseased larvae was infectious for healthy silkworm larvae, but it was not until 1947 that the German scientist Bergold discovered rod-shaped viral particles.

One of the most fruitful studies in the field of virology is Reed's study of the nature of yellow fever on US Army volunteers in 1900-1901. It has been convincingly demonstrated that yellow fever is caused by a filterable virus that is transmitted by mosquitoes and mosquitoes. It was also found that mosquitoes remained non-infectious for two weeks after absorbing infectious blood. Thus, the external incubation period of the disease (the time required for virus reproduction in an insect) was determined and the basic principles of the epidemiology of arbovirus infections (viral infections transmitted by blood-sucking arthropods) were established.

The ability of plant viruses to reproduce in their vector, an insect, was demonstrated in 1952 by Maramorosh. The researcher, using insect injection techniques, convincingly demonstrated the ability of the aster jaundice virus to multiply in its vector, the six-spotted cicada.

Stages of development of virology

The history of achievements in virology is directly related to the success of the development of the methodological base of research.

The end of the 19th - the beginning of the 20th century. The main method of identifying viruses during this period was the method of filtration through bacteriological filters (Chamberlan candles), which were used as a means of separating pathogens into bacteria and non-bacteria. Using filterability through bacteriological filters, the following viruses were discovered:

– 1892 – tobacco mosaic virus;

– 1898 – foot and mouth disease virus;

– 1899 – rinderpest virus;

– 1900 – yellow fever virus;

– 1902 – fowl and sheep pox virus;

– 1903 – rabies virus and swine fever virus;

– 1904 – human smallpox virus;

– 1905 – canine distemper virus and vaccine virus;

– 1907 – dengue virus;

– 1908 – smallpox and trachoma virus;

– 1909 – polio virus;

– 1911 – Rous sarcoma virus;

– 1915 – bacteriophages;

– 1916 – measles virus;

– 1917 – herpes virus;

– 1926 – vesicular stomatitis virus.

30s– the main virological method used for the isolation of viruses and their further identification are laboratory animals (white mice - for influenza viruses, newborn mice - for Coxsackie viruses, chimpanzees - for hepatitis B virus, chickens, pigeons - for oncogenic viruses, gnotobiont piglets – for intestinal viruses, etc.). The first person to systematically use laboratory animals in the study of viruses was Pasteur, who, back in 1881, conducted research on inoculating material from rabies patients into the brain of a rabbit. Another milestone was work on the study of yellow fever, which resulted in the use of newborn mice in virological practice. The culmination of this cycle of work was the isolation by Cycles in 1948 of a group of epidemic myalgia viruses using suckling mice.

1931 - chicken embryos, which are highly sensitive to influenza, smallpox, leukemia, chicken sarcoma and some other viruses, began to be used as an experimental model for isolating viruses. And currently, chicken embryos are widely used to isolate influenza viruses.

1932 - English chemist Alford creates artificial finely porous colloidal membranes - the basis for the ultrafiltration method, with the help of which it became possible to determine the size of viral particles and differentiate viruses on this basis.

1935 - the use of the centrifugation method made it possible to crystallize the tobacco mosaic virus. Currently, centrifugation and ultracentrifugation methods (acceleration at the bottom of the tube exceeds 200,000 g) are widely used for the isolation and purification of viruses.

In 1939, an electron microscope with a resolution of 0.2 to 0.3 nm was used for the first time to study viruses. The use of ultrathin tissue sections and the method of negative contrasting of aqueous suspensions made it possible to study the interaction of viruses with cells and to study the structure (architecture) of virions. The information obtained using the electron microscope was significantly expanded by X-ray diffraction analysis of crystals and pseudocrystals of viruses. The improvement of electron microscopes culminated in the creation of scanning microscopes that make it possible to obtain three-dimensional images. Using electron microscopy, the architecture of virions and the features of their penetration into the host cell were studied.

During this period, the bulk of viruses were discovered. Examples include the following:

– 1931 – swine influenza virus and equine western encephalomyelitis virus;

– 1933 – human influenza virus and eastern equine encephalomyelitis virus;

– 1934 – mumps virus;

– 1936 – mouse mammary cancer virus;

– 1937 – tick-borne encephalitis virus.

40s. In 1940, Hoagland and his colleagues discovered that the vaccinia virus contains DNA but not RNA. It became obvious that viruses differ from bacteria not only in size and inability to grow without cells, but also in that they contain only one type of nucleic acid - DNA or RNA.

1941 - American scientist Hurst discovered the phenomenon of hemagglutination (erythrocyte gluing) using a model of the influenza virus. This discovery formed the basis for the development of methods for detecting and identifying viruses and contributed to the study of virus-cell interactions. The principle of hemagglutination is the basis of a number of methods:

HRA - hemagglutination reaction - used to detect and titrate viruses;

HAI - hemagglutination inhibition reaction - is used to identify and titrate viruses.

1942 - Hearst discovers the presence of an enzyme in the influenza virus, which is later identified as neuraminidase.

1949 – discovery of the possibility of culturing animal tissue cells under artificial conditions. In 1952, Enders, Weller and Robbins received the Nobel Prize for developing the cell culture method.

The introduction of the cell culture method into virology was an important event that made it possible to obtain cultured vaccines. Of the currently widely used cultural live and killed vaccines created on the basis of attenuated strains of viruses, vaccines against polio, mumps, measles and rubella should be noted.

The creators of polio vaccines are American virologists Sabin (a trivalent live vaccine based on attenuated strains of polioviruses of three serotypes) and Salk (a killed trivalent vaccine). In our country, Soviet virologists M.P. Chumakov and A.A. Smorodintsev developed a technology for the production of live and killed polio vaccines. In 1988, the World Health Assembly set WHO the goal of eradicating polio worldwide by completely stopping the circulation of wild poliovirus. To date, enormous progress has been made in this direction. The use of global vaccination against polio using “round” vaccination schemes made it possible not only to radically reduce the incidence, but also to create areas free from the circulation of wild poliovirus.

Viruses discovered:

– 1945 – Crimean hemorrhagic fever virus;

– 1948 – Coxsackie viruses.

50s. In 1952, Dulbecco developed a method for titrating plaques in a monolayer of chicken embryo cells, which introduced a quantitative aspect to virology. 1956-62 Watson, Caspar (USA) and Klug (Great Britain) develop a general theory of the symmetry of viral particles. The structure of the viral particle has become one of the criteria in the virus classification system.

This period was characterized by significant advances in the field of bacteriophages:

– induction of the prophage of lysogenizing phages was established (Lvov et al., 1950);

– it has been proven that infectivity is inherent in phage DNA, and not in the protein shell (Hershey, Chase, 1952);

– the phenomenon of general transduction was discovered (Zinder, Lederberg, 1952).

The infectious tobacco mosaic virus was reconstructed (Frenkel-Conrad, Williams, Singer, 1955-1957), and in 1955 the polio virus was obtained in crystalline form (Shaffer, Shwerd, 1955).

Viruses discovered:

– 1951 – murine leukemia viruses and ECHO;

– 1953 – adenoviruses;

– 1954 – rubella virus;

– 1956 – parainfluenza viruses, cytomegalovirus, respiratory syncytial virus;

– 1957 – polyoma virus;

– 1959 – Argentine hemorrhagic fever virus.

60s characterized by the flourishing of molecular biological research methods. Advances in the field of chemistry, physics, molecular biology and genetics formed the basis of the methodological base of scientific research, which began to be used not only at the level of techniques, but also entire technologies, where viruses act not only as an object of research, but also as a tool. Not a single discovery in molecular biology is complete without a viral model.

1967 – Cates and McAuslan demonstrate the presence of a DNA-dependent RNA polymerase in the vaccinia virion. The following year, RNA-dependent RNA polymerase was discovered in reoviruses, and then in paramyxo- and rhabdoviruses. In 1968, Jacobson and Baltimore established that polioviruses have a genomic protein connected to RNA; Baltimore and Boston established that the poliovirus genomic RNA is translated into a polyprotein.

Viruses discovered:

– 1960 – rhinoviruses;

– 1963 – Australian antigen (HBsAg).

70s. Baltimore, simultaneously with Temin and Mizutani, reported the discovery of the enzyme reverse transcriptase (revertase) in RNA-containing oncogenic viruses. It is becoming possible to study the genome of RNA viruses.

The study of gene expression in eukaryotic viruses provided fundamental information about the molecular biology of eukaryotes themselves - the existence of the cap structure of mRNA and its role in RNA translation, the presence of a polyadenylate sequence at the 3" end of mRNA, splicing and the role of enhancers in transcription were first identified in the study of animal viruses.

1972 - Berg publishes a report on the creation of a recombinant DNA molecule. A new branch of molecular biology is emerging - genetic engineering. The use of recombinant DNA technology makes it possible to obtain proteins that are important in medicine (insulin, interferon, vaccines). 1975 - Köhler and Milstein produce the first lines of hybrids producing monoclonal antibodies (mAbs). The most specific test systems for diagnosing viral infections are being developed based on mAbs. 1976 - Blumberg receives the Nobel Prize for the discovery of HBsAg. It has been established that hepatitis A and hepatitis B are caused by different viruses.

Viruses discovered:

– 1970 – hepatitis B virus;

– 1973 – rotaviruses, hepatitis A virus;

– 1977 – hepatitis delta virus.

80s. Development of the ideas laid down by domestic scientist L.A. Zilber's idea that the occurrence of tumors may be associated with viruses. The components of viruses responsible for the development of tumors are called oncogenes. Viral oncogenes have proven to be among the best model systems that help study the mechanisms of oncogenetic transformation of mammalian cells.

– 1985 – Mullis receives the Nobel Prize for the discovery of the polymerase chain reaction (PCR). This is a molecular genetic diagnostic method, which has also made it possible to improve the technology for obtaining recombinant DNA and discover new viruses.

Viruses discovered:

– 1983 – human immunodeficiency virus;

– 1989 – hepatitis C virus;

– 1995 – the hepatitis G virus was discovered using PCR.

Related information.

Virology as a science

HISTORY OF VIRUSOLOGY

The history of virology is unusual in that one of its subjects—viral diseases—began to be studied long before viruses themselves were discovered. The history of virology begins with the fight against infectious diseases and only subsequently with the gradual discovery of the sources of these diseases. This is confirmed by the work of Edward Jenner (1749-1823) on the prevention of smallpox and the work of Louis Pasteur (1822-1895) with the causative agent of rabies.
By the end of the 19th century, it became clear that a number of human diseases, such as rabies, smallpox, influenza, and yellow fever, are infectious, but their causative agents were not detected by bacteriological methods.
Thanks to the work of Robert Koch (1843-1910), who pioneered the use of pure bacterial culture techniques, it became possible to distinguish between bacterial and non-bacterial diseases. In 1890, at the X Congress of Hygienists, Koch was forced to declare that “... with the diseases listed, we are not dealing with bacteria, but with organized pathogens that belong to a completely different group of microorganisms.” This statement by Koch indicates that the discovery of viruses was not a random event. Not only the experience of working with pathogens that were incomprehensible in nature, but also an understanding of the essence of what was happening contributed to the formulation of the idea of ​​the existence of an original group of pathogens of infectious diseases of a non-bacterial nature. It remained to experimentally prove its existence.

The first experimental evidence of the existence of a new group of pathogens of infectious diseases was obtained by our compatriot, plant physiologist Dmitry Iosifovich Ivanovsky (1864-1920), while studying mosaic diseases of tobacco. This is not surprising, since infectious diseases of an epidemic nature were often observed in plants. Back in 1883-84. The Dutch botanist and geneticist de Vries observed an epidemic of greening of flowers and suggested the infectious nature of the disease. In 1886, the German scientist Mayer, working in Holland, showed that the sap of plants suffering from mosaic disease, when inoculated, causes the same disease in plants. Mayer was sure that the culprit of the disease was a microorganism, and searched for it without success. In the 19th century, tobacco diseases caused enormous harm to agriculture in our country. In this regard, a group of researchers was sent to Ukraine to study tobacco diseases, which, as a student at St. Petersburg University, included D.I. Ivanovsky. As a result of studying the disease described in 1886 by Mayer as mosaic disease of tobacco, D.I. Ivanovsky and V.V. Polovtsev came to the conclusion that it represents two different diseases. One of them, “grouse,” is caused by a fungus, and the other is of unknown origin. The study of tobacco mosaic disease was continued by Ivanovsky at the Nikitsky Botanical Garden under the leadership of Academician A.S. Famytsina. Using the juice of a diseased tobacco leaf, filtered through a Chamberlant candle, which retains the smallest bacteria, Ivanovsky caused a disease of tobacco leaves. Cultivation of the infected juice on artificial nutrient media did not produce results and Ivanovsky comes to the conclusion that the causative agent of the disease is of an unusual nature - it is filtered through bacterial filters and is not able to grow on artificial nutrient media. Warming the juice at 60-70 °C deprived it of infectivity, which indicated the living nature of the pathogen. Ivanovsky first named the new type of pathogen “filterable bacteria.” Results of the work of D.I. Ivanovsky were used as the basis for his dissertation, presented in 1888, and published in the book “On Two Diseases of Tobacco” in 1892. This year is considered the year of the discovery of viruses.
For a certain period of time, in foreign publications, the discovery of viruses was associated with the name of the Dutch scientist Beijerinck (1851-1931), who also studied tobacco mosaic disease and published his experiments in 1898. Beijerinck placed the filtered juice of an infected plant on the surface of an agar, incubated and obtained bacterial colonies on its surface. After this, the top layer of agar with bacterial colonies was removed, and the inner layer was used to infect a healthy plant. The plant is sick. From this, Beijerinck concluded that the cause of the disease was not bacteria, but some liquid substance that could penetrate inside the agar, and called the pathogen “liquid living contagion.” Due to the fact that Ivanovsky only described his experiments in detail, but did not pay due attention to the nonbacterial nature of the pathogen, a misunderstanding of the situation arose. Ivanovsky’s work became famous only after Beijerinck repeated and expanded his experiments and emphasized that Ivanovsky was the first to prove the non-bacterial nature of the causative agent of the most typical viral disease of tobacco. Beijerinck himself recognized the primacy of Ivanovsky and the current priority of the discovery of viruses by D.I. Ivanovsky is recognized throughout the world.
The word VIRUS means poison. This term was also used by Pasteur to denote an infectious principle. It should be noted that at the beginning of the 19th century, all pathogenic agents were called the word virus. Only after the nature of bacteria, poisons and toxins became clear, the terms “ultravirus” and then simply “virus” began to mean “a new type of filterable pathogen.” The term “virus” took root widely in the 30s of our century.
Viruses are a unique class, the smallest class of infectious agents that pass through bacterial filters and differ from bacteria in their morphology, physiology and method of reproduction.
Viruses are extracellular life forms, the super-kingdom of the Nuclear-Free (accaryotes), the kingdom of Vir.
It is now clear that viruses are characterized by ubiquity, that is, ubiquity of distribution. Viruses infect representatives of all living kingdoms: humans, vertebrates and invertebrates, plants, fungi, bacteria.

VIRUS SIZES

Viruses are the smallest agents, 10-350 nm (0.01-0.35 microns). They are not visible with a regular light microscope, and various methods are used to determine the size of viruses:
1. filtration through filters with known pore sizes;
2. determination of the sedimentation rate of particles during centrifugation;
3. photography in an electron microscope.

CHEMICAL COMPOSITION OF VIRUSES

Viruses have three main components: protein, NK, and ash component.

Protein
Proteins are built from amino acids (a/k) of the L-series. All a/c are of trivial nature; as a rule, neutral and acidic dicarboxylic acids predominate in the structure. Complex viruses contain basic histone-like proteins associated with NK to stabilize the structure and increase antigenic activity.
All viral proteins are divided into: structural - form the protein shell - capsid; functional - enzyme proteins, some of the enzyme proteins are located in the structure of the capsid, these proteins are associated with enzymatic activity and the ability of the virus to penetrate into the cell (for example, ATPase, sialase - neiromeidase, which are found in the structure of the human and animal virus, as well as lysozyme).
The capsid consists of long polypeptide chains that may consist of one or more proteins with a small molecular weight. In the structure of the polypeptide chain, chemical, structural and morphological units are distinguished.
A chemical unit is a single protein that forms a polypeptide chain.
A structural unit is a repeating unit in the structure of a polypeptide chain.
The morphological unit is the capsomere, which is observed in the structure of the virus, which is visible in an electron microscope.
Viral capsid proteins have a number of properties: they are resistant to proteases and the reason for resistance is that the protein is organized in such a way that the peptide bond on which the protease acts is hidden inside. Such stability has a great biological meaning: since the viral particle is collected inside the cell, where the concentration of proteolytic enzymes is high. This stability protects the viral particle from destruction inside the cell. At the same time, this resistance of the viral envelope to proteolytic enzymes is lost when the viral particle passes through the cell membrane, in particular through the CPM.
It is assumed that during the transport of the viral particle through the CPM, changes in the conformational structure occur and the peptide bond becomes accessible to enzymes.
Functions of structural proteins:
- protective (protect the NK, which is located inside the capsid);
- some capsid proteins have a targeting function, which is considered as viral receptors, with the help of which the viral particle attaches to the surface of specific cells;
- an internal histone-like protein associated with NK was found in the virions, which has an antigenic function and is also involved in the stabilization of NK.
Functional enzyme proteins associated with the capsod:
- sialase-neuromyedase. Found in animal and human viruses, it facilitates the exit of the viral particle from the cell and makes a hole (bald patch) in the viral structures;
- lysozyme. Structurally related to the viral particle, it destroys the β-1,4-glycosidic part in the murein framework and facilitates the penetration of bacteriophage NK into the bacterial cell.
- ATPase. Built into the structure of bacteriophage and some human and animal viruses of cellular origin. The functions were studied using the example of bacteriophages; with the help of ATPase, ATP is hydrolyzed, which are intercalated into the structure of the virus and are of cellular origin, the released energy is consumed by contraction of the tail process, this facilitates the transport of NK into the bacterial cell.

Nucleic acids (NA)
The molecular weight of viral DNA ranges from 106-108 D, and RNA - less than 106-107 D.
The NK of viruses is 10 times smaller than the NK of the smallest cells.
The number of nucleotides in DNA varies from several thousand to 250 thousand nucleotides. 1 gene - 1000 nucleotides, this means that in the structure of viruses there are from 10 to 250 genes.
In the composition of NC, along with five nitrogenous bases, there are also abnormal bases - bases that are fully capable of replacing standard ones: 5-hydroxymethylcytosine - completely replaces cytosine, 5-hydroxymethyluracil - replaces thymine.
Anomalous bases are found only in bacteriophages; the rest have classical bases.
Functions of abnormal bases: block cellular DNA, preventing the information contained in the DNA from being realized at the moment when the viral particle enters the cell.
In addition to abnormal ones, minor bases were also found: a small amount of 5-methylcytosine, 6-methylamino purine.
Some viruses may contain methylated derivatives of cytosine and adenine.
NK viruses, both RNA and DNA, can be found in two forms:
- in the form of ring chains;
- in the form of linear molecules.

Ring chains come in two forms:
- covalently closed chains (do not have 3’ - 5’ free ends, exonucleases do not act on them);
- relaxed form, when one chain is covalently closed, and the second has one or more breaks in its structure.
Linear molecules are divided into two groups:
- linear structure with a fixed sequence of nucleotides (it always starts with one nucleotide);
- linear structure with a permitted sequence (a certain set of nucleotides, but the sequence is variable).
The structure of RNA contains single-stranded +RNA and −RNA chains.
+RNA is, on the one hand, the keeper of genetic information, and on the other hand, it performs the function of mRNA and is recognized by the ribosomes of the cell as mRNA.
−RNA − perform only the function of storing genetic information, and mRNA is synthesized on its basis.

Ash component
Viral particles contain metal cations: potassium, sodium, calcium, manganese, magnesium, iron, copper, and their content can reach several mg per 1 g of viral mass.
Me2+ functions: play an important role in stabilizing the viral NK, forming an ordered quaternary structure of the viral particle. The composition of metals is not constant and is determined by the composition of the environment. Some viruses have polycations associated with polyamines, which play a huge role in the physical stability of viral particles. Also, metal ions provide neutralization of the negative charge of NCs, which form phosphoric acid (phosphate groups) of NCs.

Municipal state educational institution

"Secondary school No. 3"

Stavropol region, Stepnovsky district,
Bogdanovka village

MKOU secondary school No. 3, 10th grade student
Scientific adviser:

Toboeva Natalya Konstantinovna
teacher of geography, biology, MKOU secondary school No. 3

I .Introduction

II.Main part:

1. Discovery of viruses

2.Origin of viruses

3. Structure

4.Penetration into the cell

5.Flu

6. Chicken pox 7. Tick-borne encephalitis 8. The future of virology

III.Conclusion

IV. Bibliography

V.Appendix

Object of study:

Non-cellular life forms are viruses.

Subject of study:

The present and future of virology.

Goal of the work:

Find out the significance of virology at the present time and determine its future. The set goal could be achieved as a result of solving the following tasks:

1) study of literature covering the structure of viruses as non-cellular life forms;

2) research into the causes of viral diseases, as well as their prevention.

This determined the topic of my research.

I. Introduction.

The action-packed and fascinating history of virology is characterized by triumphant victories, but, unfortunately, also defeats. The development of virology is associated with the brilliant successes of molecular genetics.

The study of viruses has led to an understanding of the fine structure of genes, deciphering the genetic code, and identifying the mechanisms of mutations.

Viruses are widely used in genetic engineering and research.

But their cunning and ability to adapt know no bounds, their behavior in each case is unpredictable. The victims of viruses are millions of people who died from smallpox, yellow fever, AIDS and other diseases. Much remains to be discovered and learned. And yet, the main successes in virology have been achieved in the fight against specific diseases. That is why scientists say that virology will take a leading place in the third millennium.

What has virology given to humanity in the fight against its formidable enemy - the virus? What is its structure, where and how does it live, how does it reproduce, what other “surprises” does it prepare? I considered these questions in my work.

II.Main part:

1. Discovery of viruses.

The discoverer of the world of viruses was the Russian botanist D.I. Ivanovsky. In 1891-1892 he persistently searched for the causative agent of tobacco mosaic disease. The scientist examined the liquid obtained by rubbing diseased tobacco leaves. I filtered it through filters that were not supposed to let a single bacteria through. Patiently, he pumped liters of juice taken from mosaic tobacco leaves into hollow bacterial filters made of finely porous porcelain, reminiscent of long candles. The walls of the filter sweated with transparent droplets that flowed into a pre-sterilized vessel. By lightly rubbing, the scientist applied a drop of this filtered juice to the surface of the tobacco leaf. After 7-10 days, undoubted signs of mosaic disease appeared in previously healthy plants. A drop of filtered juice from an infected plant affected any other tobacco bush with a mosaic disease. The infestation could pass from plant to plant endlessly, like a flame of fire from one thatched roof to another.

Subsequently, it was possible to establish that many other viral pathogens of infectious diseases in humans, animals and plants are capable of passing through, which could be seen through the most advanced light microscopes. Particles of various viruses could only be seen through the window of an all-seeing device - an electron microscope, which provides a magnification of hundreds of thousands of times.

D.I. himself Ivanovsky did not attach much importance to this fact, although he described his experience in detail.

His work gained fame after the Dutch botanist and microbiologist Martin Beijerinck confirmed the results of D. I. Ivanovsky’s research in 1899. M. Beyerinck proved that the mosaic of tobacco can be transferred from one plant to another using filtrates. These studies marked the beginning of the study of viruses and the emergence of virology as a science.

2. Origin of viruses.

3. Structure.

Being completely primitive creatures, viruses have all the basic properties of living organisms. They reproduce offspring similar to the original parental forms, although their method of reproduction is peculiar and differs in many respects from what is known about the reproduction of other creatures. Their metabolism is closely related to the metabolism of host cells. They have heredity characteristic of all living organisms. Finally, they, like all other living beings, are characterized by variability and adaptability to changing environmental conditions.

The largest viruses (for example, smallpox viruses) reach a size of 400-700 nm and are close in size to small bacteria, the smallest (causative agents of polio, encephalitis, foot-and-mouth disease) measure only tens of nanometers, i.e. are close to large protein molecules, in particular blood hemoglobin molecules.

Viruses come in a variety of shapes, from spherical to filamentous. Electron microscopy allows not only to see viruses, determine their shapes and sizes, but also to study their spatial structure - molecular architectonics.

A relatively simple composition is typical for viruses: nucleic acid (RNA or DNA), protein; more complex structures contain carbohydrates and lipids, and sometimes have a number of their own enzymes.

As a rule, the nucleic acid is located in the center of the viral particle and is protected from adverse effects by a protein shell - capsomers. Electron microscope observations showed that the virus particle

(or virions) come in several basic types in shape.

Some viruses (usually the simplest ones) resemble regular geometric bodies. Their protein shell almost always approaches the shape of an icosahedron (regular twenty-sided structure) with faces of equilateral triangles. These virions are called cubic (such as the polio virus). The nucleic acid of such a virus is often twisted into a ball. Particles of other viruses are shaped like oblong rods. In this case, their nucleic acid is surrounded by a cylindrical capsid. Such virions are called helical virions (for example, tobacco mosaic virus).

Viruses of a more complex structure, in addition to the icosahedral or helical capsid, also have an outer shell, which consists of a variety of proteins (many of them enzymes), as well as lipids and carbons.

The physical structure of the outer shell is very varied and is not as compact as that of the capsid. For example, the herpes virus is an enveloped helical virion. There are viruses with an even more complex structure. Thus, the smallpox virus does not have a visible capsid (protein shell), but its nucleic acid is surrounded by several shells.

4.Penetration into the cell.

As a rule, the penetration of the virus into the cytoplasm of the cell is preceded by its binding to a special receptor protein located on the cell surface. Binding to the receptor occurs due to the presence of special proteins on the surface of the viral cell. The area of ​​the cell surface to which the virus has attached is immersed in the cytoplasm and turns into a vacuole. A vacuole is a wall that consists of a cytoplasmic membrane that can merge with other vacuoles or the nucleus. This way the virus is delivered to any part of the cell.

The receptor mechanism for virus penetration into the cell ensures the specificity of the infectious process. The infectious process begins when viruses that have entered the cell begin to multiply, i.e. The viral genome is reduplicated and the capsid self-assembles. For reduplication to occur, the nucleic acid must be freed from the capsid. After the synthesis of a new nucleic acid molecule, it is dressed with viral proteins synthesized in the cytoplasm of the host cell - a capsid is formed.

The accumulation of viral particles leads to elimination from the cell. For some viruses, this occurs through an “explosion,” in which the integrity of the cell is disrupted and it dies. Other viruses are released in a manner reminiscent of budding. In this case, the cells can maintain their viability.

Bacteriophage viruses have a different way of entering cells. The bacteriophage inserts a full rod into the cell and pushes out the DNA (or RNA) found in its head through it. The bacteriophage genome enters

cytoplasm, and the capsid remains outside. In the bacterial cytoplasm, the reduplication of the bacteriophage genome, the synthesis of its proteins and the formation of the capsid begin. After a certain period of time, the bacterial cell dies and mature particles enter the environment.

5.Flu.

Influenza is an acute infectious disease, the causative agent of which is a filter virus, causing general intoxication and damage to the mucous membrane of the upper respiratory tract.

It has now been established that the influenza virus has several serological types, differing in their antigenic structure.

There are the following types of influenza virus: A, B, C, D. Virus A has 2 subtypes, designated:A 1 and A2.

The influenza virus outside the human body is unstable and dies quickly. The virus dried in a vacuum can persist for a long time.

Disinfectants quickly destroy the virus; ultraviolet radiation and heat also have a detrimental effect on the virus.

Allow the possibility of infection from a virus carrier. The virus is transmitted from a sick person to a healthy person through airborne droplets. Coughing and sneezing contribute to the spread of infection.

Viral influenza epidemics most often occur during the cold season.

A person with the flu is contagious for 5-7 days. All people who have not had the flu are susceptible to this disease. After suffering from the flu, immunity remains for 2-3 years.

The incubation period is short - from several hours to 3 days. Most often 1-2 days.

Usually there are no prodromes, and a sudden onset is typical. Chills, headache, general weakness appear, and the temperature rises to 39-40 degrees. Patients complain of pain when rotating the eyes, aching muscle joints, disturbed sleep, and sweating. All this indicates general intoxication with the involvement of the nervous system in the process.

The central nervous system is especially sensitive to the toxic effects of the influenza virus, which is clinically expressed in severe adynamia, irritability, and decreased sense of smell and taste.

On the part of the digestive tract, the phenomena of influenza intoxication also differ: decreased appetite, stool retention, and sometimes, more often in young children, diarrhea.

The tongue is coated and slightly swollen, which leads to the appearance of teeth marks along the edges. The temperature remains elevated for 3-5 days and, in the absence of complications, drops to normal gradually or drops critically.

After 1-2 days, a runny nose, laryngitis, and bronchitis may appear. Bleeding from the nose is common. The cough is dry at first and turns into a cough with sputum. Vascular disorders are expressed in the form of low blood pressure, pulse instability and disturbances in its rhythm.

Uncomplicated flu usually ends within 3-5 days, however, full recovery takes 1-2 weeks.

Like any infection, influenza can occur in mild, severe, hypertoxic and fulminant forms.

Along with this, viral flu can be extremely mild and spread on the legs, ending within 1-2 days. These forms of influenza are called erased.

Influenza infection can cause complications in various organ systems. Most often in children, the flu is complicated by pneumonia, otitis media, which is accompanied by fever, anxiety, and sleep disturbances.

Complications from the peripheral nervous system are expressed in the form of neuralgia, neuritis, radiculitis.

Treatment:

The patient must be provided with bed rest and rest. Bed rest must be maintained for some time, even after the temperature drops. Systematic ventilation of the room, daily warm or hot baths, good nutrition - all this increases the body's resistance to fighting the flu.

Specific treatment of viral influenza is carried out using the anti-influenza polyvalent serum proposed by A.A. Smorodintsev.

Among the symptomatic remedies for headache, muscle and joint pain, as well as neurological pain, pyramidon, phenacetin, and aspirin with caffeine are prescribed.

In case of severe toxicosis, intravenous glucose is prescribed. For uncomplicated influenza, antibiotics are not used, because They no longer work on the virus. For a dry cough, hot milk with soda or Borjomi is useful.

Prevention:

Patients should be isolated at home or in hospitals. If the patient is left at home, it is necessary to place him in a separate room or separate his bed with a screen or sheet. Caregivers should wear a gauze mask covering the nose and mouth.

6. Chicken pox.

Chickenpox is an acute infectious disease caused by a virus and characterized by a macular vesicular rash on the skin and mucous membranes.

The causative agent of chickenpox is a filter virus and is found in chickenpox vesicles and in the blood. The virus is unstable and exposed to various environmental influences and dies quickly.

The source of infection is the patient, who is contagious during the period of rash and at the end of incubation. The infection is spread by airborne droplets. The disease is not transmitted through objects.

Immunity after chickenpox remains for life. The incubation period lasts from 11 to 21 days, with an average of 14 days.

In most cases, the disease begins immediately, and only sometimes there are precursors in the form of a moderate increase in temperature with symptoms of general malaise. Prodromes may be accompanied by a rash resembling scarlet fever or measles.

With a moderate rise in temperature, a spotted rash of varying sizes appears on different parts of the body - from a pinhead to a lentil. Over the next few hours, a bubble with transparent contents, surrounded by a red rim, forms in place of the spots. Chickenpox blisters (vesicles) are located on unchanged skin, tender and soft to the touch. The contents of the bubble soon become cloudy, and the bubble itself bursts (2-3 days) and turns into a crust, which disappears after 2-3 weeks, usually leaving no scar. The rash and subsequent formation of blisters can be abundant, affecting the entire scalp, trunk, and limbs, while on the face and distal parts of the limbs they are less abundant.

The course of chickenpox is usually accompanied by a slight disturbance in the general condition of the patient. Each new rash causes an increase in temperature to 38° and above. At the same time, appetite decreases.

In addition to the skin, chicken rash can affect the mucous membranes of the oral cavity, conjunctiva, genitals, larynx, etc.

Treatment:

Bed linen must always be clean. Take warm baths (35°-37°) from weak solutions of potassium permanganate. The patient's hands should be clean with short-cut nails.

Individual bubbles are lubricated with iodine or potassium solution, 1% alcohol solution of brilliant green.

For purulent complications caused by secondary infection, treatment is carried out with antibiotics (penicillin, streptomycin, biomycin)

Prevention:

A person infected with chickenpox must be isolated at home. Disinfection is not carried out, the room is ventilated and subjected to wet cleaning.

7. Tick-borne encephalitis.

An acute viral disease characterized by damage to the gray matter of the brain and spinal cord. The reservoir for sources of infection are wild animals (mainly rodents) and ixodid ticks. Infection is possible not only by sucking on a tick, but also by consuming the milk of infected goats. The causative agent is an arbovirus. The gateway of infection is the skin (if ticks are sucked on) or the mucous membrane of the digestive tract (if there is alimentary infection). The virus hematogenously penetrates the central nervous system and causes the most pronounced changes in the nerve cells of the anterior horns of the cervical spinal cord and in the nuclei of the medulla oblongata.

The incubation period is from 8 to 23 days (usually 7-14 days). The disease begins acutely: chills, severe headache, and weakness appear. After encephalitis, lasting consequences may remain in the form of flaccid paralysis of the muscles of the neck and shoulder girdle.

Treatment:

Strict bed rest:

for mild forms - 7-10 days,

for moderate cases - 2-3 weeks,

for severe ones - even longer.

Prevention:

When a tick bites in an area unfavorable for encephalitis, it is necessary to administer anti-encephalitis gamma globulin. According to indications, preventive vaccination is carried out.

8.The future of virology.

What are the prospects for the development of virology in the 21st century? In the second half of the 20th century, progress in virology was associated with classical discoveries in biochemistry, genetics and molecular biology. Modern virology is intertwined with the successes of fundamental applied sciences, so its further development will follow the path of in-depth study of the molecular basis of the pathogenicity of viruses of new previously unknown pathogens (prions and virions), the nature and mechanisms of persistence of viruses, their ecology, the development of new and improvement of existing diagnostic methods and specific prevention of viral diseases.

There is currently no more important aspect in virology than the prevention of infections. Over the 100 years of the existence of the science of viruses and viral diseases, vaccines have undergone great changes, going from attenuated and killed vaccines from the time of Pasteur to modern genetically engineered and synthetic vaccine preparations. This direction will continue to develop, based on physicochemical genetic engineering and synthetic experiments with the goal of creating polyvalent vaccines that require minimal vaccinations as early as possible after birth. Chemotherapy will develop, an approach relatively new to virology. These drugs are so far useful only in isolated cases.

III. Conclusion.

Humanity faces many complex unsolved virological problems: hidden viral infections, viruses and tumors, etc. The level of development of virology today, however, is such that means of combating infections will definitely be found. It is very important to understand that viruses are not an element alien to living nature; they are a necessary component of the biosphere, without which adaptation, evolution, immune defense and other interactions of living objects with their environment would probably be impossible. Understanding viral diseases as pathologies of adaptation, the fight against them should be aimed at improving the status of the immune system, and not at destroying viruses.

Analysis of various literary sources and statistical data allowed us to draw the following conclusions:

viruses are autonomous genetic compounds of structure that are unable to develop outside the cell;

3) come in a variety of shapes and simple composition.

Bibliography:

1. Great Soviet Encyclopedia: T.8 / Ed. B.A. Vvedensky.

2. Denisov I.N., Ulumbaev E.G. Directory - a guide for a practicing physician. - M.: Medicine, 1999.

3. Zverev I.D. A book for reading on human anatomy, physiology and hygiene. - M.: Education, 1983.

4. Luria S. et al. General virology. - M.: Mir, 1981.

6. Pokrovsky V.I. Popular medical encyclopedia. - M.: Onyx, 1998.

7.Tokarik E.N. Virology: present and future // Biology at school. - 2000. - No. 2-3.

Virology.

Other mycoplasmas pathogenic for humans.

Mycoplasma pneumonia.

Mycoplasma pneumoniae.

M. pneumoniae differs from other species by serology, as well as by characteristics such as b-hemolysis of sheep red blood cells, aerobic reduction of tetrazolium, and the ability to grow in the presence of methylene blue.

M. pneumoniae is the most common cause of nonbacterial pneumonia. Infection with this mycoplasma may also take the form of bronchitis or mild respiratory fever.

Asymptomatic infections are common. Familial outbreaks are common, and large outbreaks have occurred in military training centers. The incubation period is approximately two weeks.

M. pneumoniae can be isolated by culture of sputum and throat swabs, but the diagnosis is more easily made by serological methods, usually the complement fixation test. The diagnosis of mycoplasma pneumonia is helped by the empirical finding that many patients form cold agglutinins to human red blood cells of group 0.

Mycoplasmas are normally inhabitants of the reproductive tract of men and women. The most commonly encountered species is M. hominis, which is responsible for some cases of vaginal discharge, urethritis, salpingitis and pelvic sepsis. It is the most common cause of postpartum sepsis.

The microorganism can enter the mother's blood during childbirth and be localized in the joints. A group of mycoplasmas (ureaplasmas) that form tiny colonies are considered a possible cause of nongonococcal urethritis in both sexes. Other species are normal commensals of the oral cavity and nasopharynx.

Prevention. It comes down to maintaining a high level of general resistance of the human body. A vaccine made from killed mycoplasmas for the specific prevention of atypical pneumonia has been obtained in the USA

1. Pyatkin K.D., Krivoshein Yu.S. Microbiology. - K: Higher School, 1992. - 432 p.

Timakov V.D., Levashev V.S., Borisov L.B. Microbiology. - M: Medicine, 1983. - 312 p.

2. Borisov L.B., Kozmin-Sokolov B.N., Freidlin I.S. Guide to laboratory classes in medical microbiology, virology and immunology / ed. Borisova L.B. – G.: Medicine, 1993. – 232 p.

3. Medical microbiology, virology and immunology: Textbook, ed. A.A. Vorobyova. – M.: Medical Information Agency, 2004. - 691 p.

4. Medical microbiology, virology, immunology / ed. L.B.Borisov, A.M.Smirnova. - M: Medicine, 1994. - 528 p.

Odessa-2009

Lecture No. 21. Subject and tasks of medical virology. General characteristics of viruses

We are starting to study a new science - virology, the science of viruses. Virology is an independent science of modern natural science, occupying a vanguard position in biology and medicine, and the role and importance of virology is steadily increasing. This is due to a number of circumstances:

1. Viral diseases occupy a leading place in human infectious pathology. The use of antibiotics makes it possible to effectively solve the treatment of most bacterial diseases, while there are still no sufficiently effective and harmless drugs for the treatment of viral diseases. As the incidence of bacterial infections decreases, the proportion of viral diseases is steadily increasing. The problem of mass viral infections - respiratory and intestinal - is acute. For example, the well-known flu often takes the form of massive epidemics and even pandemics, in which a significant percentage of the world's population falls ill.

2. The viral-genetic theory of the origin of tumors and leukemia has gained recognition and is increasingly being confirmed. Therefore, we expect that the development of virology will lead to a solution to the most important problem of human pathology - the problem of carcinogenesis.

3. Currently, new viral diseases are emerging or previously known viral diseases are becoming acute, which constantly poses new challenges for virology. An example is HIV infection.

4. Viruses have become a classic model for molecular biology and molecular genetic research. Many questions of fundamental research in biology are solved using viruses; viruses are widely used in biotechnology.

5. Virology is a fundamental science of modern natural science, not only because it enriches other sciences with new methods and new ideas, but also because the subject of the study of virology is a qualitatively special form of organization of living matter - viruses, which are radically different from all other living beings on Earth .

2. HISTORICAL SKETCH OF THE DEVELOPMENT OF VIRUSOLOGY

The credit for the discovery of viruses and the description of their main characteristics belongs to the Russian scientist Dmitry Iosifovich Ivanovsky (1864-1920). It is interesting that Ivanovsky began his research as a 3rd year student at St. Petersburg University, when he was doing coursework in Ukraine and Bessarabia. He studied tobacco mosaic disease and found out that it was an infectious plant disease, but its causative agent did not belong to any of the then known groups of microorganisms. Later, already a certified specialist, Ivanovsky continues his research at the Nikitsky Botanical Garden (Crimea) and performs a classic experiment: he filters the juice of the leaves of the affected plant through a bacterial filter and proves that the infectious activity of the juice does not disappear.

Subsequently, the main groups of viruses were discovered. In 1898, F. Leffler and P. Frosch proved the filterability of the causative agent of foot-and-mouth disease (the foot-and-mouth disease virus affects animals and humans), in 1911, P. Raus proved the filterability of the causative agent of the tumor disease - chicken sarcoma, in 1915, F. Twort and in 1917 Mr. D'Herelle discovered phages - bacterial viruses.

This is how the main groups of viruses were discovered. Currently, more than 500 types of viruses are known.

Further progress in the development of virology is associated with the development of methods for cultivating viruses. At first, viruses were studied only when they infected sensitive organisms. A significant step forward was the development of a method for cultivating viruses in chicken embryos by Woodruff and Goodpasture in 1931. A revolution in virology was the development of a method for cultivating viruses in single-layer cell cultures by J. Enders, T. Weller, F. Robbins, and in 1948. Not without reason in 1952 This discovery was awarded the Nobel Prize.

Already in the 30s the first virological laboratories were created. Currently in Ukraine there is the Odessa Research Institute of Epidemiology and Virology named after. I.I. Mechnikov, there are virological laboratories in a number of research institutes of epidemiology, microbiology, and infectious diseases. There are virological laboratories for practical health care, which are primarily engaged in the diagnosis of viral diseases.

3. Compose the ultrastructure of viruses

First of all, it must be said that the term “virus” was introduced into scientific terminology by L. Pasteur. L. Pasteur received his vaccine to prevent rabies in 1885, although he did not discover the causative agent of this disease - there were still 7 years left before the discovery of viruses. L. Pasteur called the hypothetical pathogen the rabies virus, which translated means “rabies poison.”

The term “virus” is used to refer to any stage of virus development - both extracellularly located infectious particles and intracellularly reproducing virus. To designate a viral particle, the term “ virion».

By chemical composition Viruses are basically similar to other microorganisms; they have nucleic acids, proteins, and some also have lipids and carbohydrates.

Viruses contain only one type of nucleic acid - either DNA or RNA. Accordingly, DNA genomic and RNA genomic viruses are isolated. Nucleic acid in the virion can contain from 1 to 40%. Typically, the virion contains only one nucleic acid molecule, often closed in a ring. Viral nucleic acids are not much different from eukaryotic nucleic acids; they consist of the same nucleotides and have the same structure. True, viruses can contain not only double-stranded, but also single-stranded DNA. Some RNA viruses may contain double-stranded RNA, although most contain single-stranded RNA. It should be noted that viruses may contain plus-strand RNA, which can act as messenger RNA, but they may also contain minus-strand RNA. Such RNA can perform its genetic function only after the complementary plus strand is synthesized in the cell. Another feature of viral nucleic acids is that in some viruses the nucleic acid is infectious. This means that if RNA without protein admixture is isolated from a virus, for example the polio virus, and introduced into a cell, a viral infection will develop with the formation of new viral particles.

Proteins are contained in viruses in an amount of 50-90%; they have antigenic properties. Proteins are part of the envelope structures of the virion. In addition, there are internal proteins associated with the nucleic acid. Some viral proteins are enzymes. But these are not enzymes that ensure the metabolism of viruses. Viral enzymes are involved in the penetration of the virus into the cell, the exit of the virus from the cell, some of them are necessary for the replication of viral nucleic acids.

Lipoids can be from 0 to 50%, carbohydrates - 0 - 22%. Lipids and carbohydrates are part of the secondary shell of complex viruses and are not virus-specific. They are borrowed by the virus from the cell and are therefore cellular.

Let us note a fundamental difference in the chemical composition of viruses - the presence of only one type of nucleic acid, DNA or RNA.

Ultrastructure of viruses- this is the structure of virions. The sizes of virions vary and are measured in nanometers. 1 nm is a thousandth of a micrometer. The smallest typical viruses (poliomyelitis virus) have a diameter of about 20 nm, the largest (variola virus) - 200-250 nm. Average viruses have sizes of 60 - 120 nm. Small viruses can only be seen in an electron microscope; large ones are at the limit of the resolution of a light microscope and are visible in a dark field of view or with special staining that increases the size of the particles. Individual viral particles visible under a light microscope are usually called elementary Paschen-Morozov bodies. E. Paschen discovered the variola virus using a special stain, and Morozov proposed a silvering method that made it possible to see even medium-sized viruses in a light microscope.

The shape of virions can be different - spherical, cuboidal, rod-shaped, sperm-like.

Each virion consists of a nucleic acid, which in viruses constitutes a “nucleon.” Compare - nucleus in eukaryotes, nucleoid - in prokaryotes. The nucleon is necessarily associated with the primary protein shell - the capsid, consisting of protein capsomers. As a result, a nucleoprotein is formed - a nucleocapsid. Simple viruses consist only of a nucleocapsid (poliomyelitis viruses, tobacco mosaic disease virus). Complex viruses also have a secondary shell - a supercapsid, which in addition to proteins also contains lipids and carbohydrates.

The combination of structural elements in the virion may be different. There are three types of symmetry of viruses - helical, cubic and mixed. Speaking about symmetry, the symmetry of the viral particles relative to the axis is emphasized.

At spiral type of symmetry individual capsomeres, visible in an electron microscope, are arranged along the nucleic acid helix so that the thread passes between two capsomeres, covering it on all sides. The result is a rod-shaped structure, such as the rod-shaped tobacco mosaic virus. But viruses with a helical type of symmetry do not necessarily have to be rod-shaped. For example, although the influenza virus has a helical type of symmetry, its nucleocapsid is folded in a certain way and is covered with a supercapsid. As a result, influenza virions are usually spherical in shape.

At cubic type symmetry, the nucleic acid folds in a certain way in the center of the virion, and capsomers cover the outside of the nucleic acid, forming a three-dimensional geometric figure. Most often, the figure of an icosahedron, a polyhedron with a certain ratio of the number of vertices and faces, is formed. For example, polio viruses have this form. In profile, the virion has the shape of a hexagon. A more complex form of adenovirus, also of cubic type of symmetry. Long threads and fibers extend from the vertices of the polyhedron, ending in a thickening.

With a mixed type of symmetry, for example, in bacteriophages, the head with a cubic type of symmetry has the shape of an icosahedron, and the process contains a spirally twisted contractile fibril.

Some viruses have a more complex structure. For example, the variola virus contains a large nucleocapsid with a helical type of symmetry, and the supercapsid is complex and contains a system of tubular structures.

Thus, viruses are quite complex. But we must note that viruses do not have a cellular organization. Viruses are non-cellular creatures, and this is one of their fundamental differences from other organisms.

A few words about the stability of viruses. Most viruses are inactivated at 56 - 60 °C for 5 - 30 minutes. Viruses tolerate refrigeration well; at room temperature, most viruses are quickly inactivated. The virus is more resistant to ultraviolet radiation and ionizing radiation than bacteria. Viruses are resistant to glycerol. Antibiotics have no effect on viruses at all. Of the disinfectants, the most effective is 5% Lysol; most viruses die within 1 - 5 minutes.

4. VIRUS REPRODUCTION

Usually we do not use the term “reproduction of viruses”, but rather say “reproduction”, reproduction of viruses, since the method of reproduction of viruses is fundamentally different from the method of reproduction of all organisms known to us.

To better study the mechanism of virus reproduction, we offer you a table that is not included in textbooks, but helps to understand this complex process.

stages of virus reproduction

The first, preparatory period, begins with the stage of virus adsorption on the cell. The adsorption process is carried out due to the complementary interaction of the virus attachment proteins with cellular receptors. Cellular receptors can be of glycoprotein, glycolipid, protein and lipid nature. Each virus requires specific cellular receptors.

Viral attachment proteins located on the surface of the capsid or supercapsid act as viral receptors.

The interaction between virus and cell begins with nonspecific adsorption of the virion on the cell membrane, and then specific interaction between viral and cellular receptors occurs according to the principle of complementarity. Therefore, the process of virus adsorption on a cell is a specific process. If the body does not have cells with receptors for a particular virus, then infection with this type of virus in such an organism is impossible - there is species resistance. On the other hand, if we could block this first stage of interaction between the virus and the cell, then we could prevent the development of a viral infection at a very early stage.

Stage 2 - penetration of the virus into the cell - can occur in two main ways. The first one, which was described earlier, is called viropexis. This pathway closely resembles phagocytosis and is a variant of receptor endocytosis. The viral particle is adsorbed on the cell membrane; as a result of the interaction of receptors, the state of the membrane changes, and it invaginates, as if flowing around the viral particle. A vacuole is formed, delimited by a cell membrane, in the center of which the viral particle is located.

When a virus enters through membrane fusion mutual penetration of the elements of the virus shell and the cell membrane occurs. As a result, the “core” of the virion ends up in the cytoplasm of the infected cell. This process occurs quite quickly, so it was difficult to register it on electron diffraction patterns.

Deproteinization - release of the viral genome from the supercapsid and capsid. This process is sometimes called “undressing” of virions.

Release from the membranes often begins immediately after the virion attaches to cellular receptors and continues inside the cell cytoplasm. Lysosomal enzymes take part in this. In any case, for further reproduction to occur, deproteinization of the viral nucleic acid is necessary, since without this the viral genome is not able to induce the reproduction of new virions in the infected cell.

Average reproduction period called latent, hidden, since after deproteinization the virus seems to “disappear” from the cell, it cannot be detected on electron diffraction patterns. During this period, the presence of the virus is detected only by changes in the metabolism of the host cell. The cell is rebuilt under the influence of the viral genome on the biosynthesis of the components of the virion - its nucleic acid and proteins.

First stage of the middle period, t transcription viral nucleic acids, rewriting genetic information through the synthesis of messenger RNA is a necessary process to begin the synthesis of viral components. It occurs differently depending on the type of nucleic acid.

Viral double-stranded DNA is transcribed in the same way as cellular DNA by DNA-dependent RNA polymerase. If this process is carried out in the cell nucleus (in adenoviruses), then cellular polymerase is used. If in the cytoplasm (smallpox virus), then with the help of RNA polymerase, which penetrates the cell as part of the virus.

If the RNA is minus-strand (in influenza, measles, rabies viruses), information RNA must first be synthesized on the viral RNA matrix using a special enzyme - RNA-dependent RNA polymerase, which is part of the virions and penetrates the cell along with the viral RNA. The same enzyme is also found in viruses containing double-stranded RNA (reoviruses).

Regulation of the transcription process is carried out by sequential rewriting of information from “early” and “late” genes. “Early” genes contain information about the synthesis of enzymes necessary for gene transcription and their subsequent replication. In the “late” ones there is information for the synthesis of virus envelope proteins.

Broadcast- synthesis of viral proteins. This process is completely analogous to the known scheme of protein biosynthesis. Virus-specific messenger RNA, cellular transfer RNA, ribosomes, mitochondria, and amino acids are involved. First, enzyme proteins necessary for the transcription process are synthesized, as well as for partial or complete suppression of the metabolism of the infected cell. Some virus-specific proteins are structural and are included in the virion (for example, RNA polymerase), others are non-structural, which are found only in the infected cell and are necessary for one of the processes of virion reproduction.

Later, the synthesis of viral structural proteins - components of the capsid and supercapsid - begins.

After the synthesis of viral proteins on ribosomes, their post-translational modification can occur, as a result of which the viral proteins “mature” and become functionally active. Cellular enzymes can carry out phosphorylation, sulfonation, methylation, acylation and other biochemical transformations of viral proteins. The process of proteolytic cutting of viral proteins from large-molecular precursor proteins is essential.

Replication viral genome - synthesis of viral nucleic acid molecules, reproduction of viral genetic information.

Replication of viral double-stranded DNA occurs with the help of cellular DNA polymerase in a semi-conservative manner in the same way as cellular DNA replication. Single-stranded DNA replicates through an intermediate double-stranded replicative form.

There are no enzymes in the cell that can carry out RNA replication. Therefore, such a process is always carried out by virus-specific enzymes, information about the synthesis of which is encoded in the viral genome. During the replication of single-stranded RNA genomes, an RNA strand complementary to the viral one is first synthesized, and then this newly formed RNA strand becomes the template for the synthesis of genome copies. Moreover, in contrast to the transcription process, in which often only relatively short RNA chains are synthesized, during replication a complete strand of RNA is immediately formed. Double-stranded RNA replicates similarly to double-stranded DNA, but with the help of the corresponding enzyme - RNA polymerase of viral origin.

As a result of the process of viral genome replication, funds of viral nucleic acid molecules necessary for the formation of mature virions accumulate in the cell.

Thus, the synthesis of individual components of the virion is separated in time and space, occurring in different cellular structures and at different times.

IN final period During reproduction, virions are assembled and the virus leaves the cell.

Virion assembly may occur in different ways, but it is based on the process of self-assembly of viral components transported from the sites of their synthesis to the site of assembly. The primary structure of viral nucleic acids and proteins determines the order of conformation of the molecules and their connection with each other. First, a nucleocapsid is formed due to the strictly oriented connection of protein molecules into capsomers and capsomers with nucleic acid. For simple viruses, this is where the assembly ends. The assembly of complex viruses with a supercapsid is multistage and usually ends during the process of virions leaving the cell. In this case, elements of the cell membrane are included in the supercapsid of the virus.

Exit of the virus from the cell can happen in two ways. Some viruses that lack a supercapsid (adenoviruses, picornaviruses) exit the cell in an “explosive” manner. In this case, the cell is lysed, and the virions exit the destroyed cell into the intercellular space. Other viruses that have a lipoprotein secondary envelope, for example influenza viruses, leave the cell by budding from its envelope. The cell can remain viable for a long time.

The entire virus reproduction cycle usually takes several hours. In the 4 to 5 hours that pass from the moment one molecule of viral nucleic acid enters a cell, from several tens to several hundred new virions can be formed that can infect neighboring cells. Thus, the spread of viral infection in cells occurs very quickly.

Thus, the way viruses reproduce is fundamentally different from the way all other living things reproduce. All cellular organisms reproduce by division. When viruses multiply, individual components are synthesized in different places in the virus-infected cell and at different times. This method of reproduction is called “disconnected” or “disjunctive”.

It should be said that the interaction of the virus and the cell may not necessarily lead to the described result - early or delayed death of the infected cell with the production of a mass of new mature viral particles. There are three possible types of viral infection in a cell.

The first option, which we have already discussed, occurs when productive or virulent infections.

Second option - persistent infection of a virus in a cell, when there is a very slow production of new virions with their release from the cell, but the infected cell remains viable for a long time.

Finally, the third option is integrative type interaction between a virus and a cell, during which the integration of viral nucleic acid into the cellular genome occurs. This involves the physical inclusion of a viral nucleic acid molecule into the host cell chromosome. For DNA genomic viruses, this process is quite understandable; RNA genomic viruses can integrate their genome only in the form of a “provirus” - a DNA copy of viral RNA synthesized using reverse transcriptase - RNA-dependent DNA polymerase. In the case of integration of the viral genome into the cellular genome, the viral nucleic acid replicates together with the cellular one during cell division. A virus in the form of a provirus can persist in a cell for a long time due to constant replication. This process is called " virogeny».

5. CARDINAL FEATURES OF VIRUSES

However, the size of large viruses is comparable to the size of chlamydia and small rickettsia, and filterable forms of bacteria have been described. Currently, the term “filterable viruses”, which for a long time was common to refer to viruses, is practically not used. Therefore, small size is not a fundamental difference between viruses and other living beings.

Therefore, at present, the fundamental differences between viruses and other microorganisms are based on more significant biological properties, which we discussed in this lecture.

Based on the knowledge of the properties of viruses we have analyzed, we can formulate the following 5 fundamental differences between viruses from other living beings on Earth:

1. Lack of cellular organization.

2. The presence of only one type of nucleic acid (DNA or RNA).

3. Lack of independent metabolism. Metabolism in viruses is mediated through the metabolism of cells and organisms.

4. The presence of a unique, disjunctive method of reproduction.

Thus, we can give the following definition to viruses.

History of virology. Principles of virus classification

Virology is the science that studies the morphology, physiology, genetics, ecology and evolution of viruses

The word "virus" meant poison. This term was also used by L. Pasteur to designate an infectious principle. Currently, a virus refers to tiny replicating microorganisms found wherever there are living cells.

The discovery of viruses belongs to the Russian scientist Dmitry Iosifovich Ivanovsky, who in 1892 published a work on the study of tobacco mosaic disease. D.I. Ivanovsky showed that the causative agent of this disease is very small in size and does not linger on bacterial filters, which are an insurmountable obstacle for the smallest bacteria. In addition, the causative agent of tobacco mosaic disease is not able to be cultivated on artificial nutrient media. D.I. Ivanovsky discovered plant viruses.

In 1898, Loeffler and Frosch showed that foot-and-mouth disease, a widespread cattle disease, was caused by an agent that also passed through bacterial filters. This year is considered the year of discovery of animal viruses.

In 1901, Reed and Carroll showed that filterable agents could be isolated from the corpses of people who died of yellow fever. This year is considered the year of discovery of human viruses.

D'Herrel and Twort in 1917-1918 discovered viruses in bacteria, calling them “bacteriophages.” Later, viruses were isolated from insects, fungi, and protozoa.

Viruses still remain one of the main causative agents of infectious and non-infectious human diseases. About 1000 different diseases are viral in nature. Viruses and the human diseases they cause are the object of study in medical virology.

Viruses have fundamental differences from other prokaryotic microorganisms:

1. Viruses do not have a cellular structure. These are precellular microorganisms.

2. Viruses have submicroscopic sizes, varying in human viruses from 15-30 nm to 250 nm or more.

3. Viruses contain only one type of nucleic acid: either DNA or RNA, where all the information of the virus is encoded.

4. Viruses do not have their own metabolic and energy systems.

6. Viruses are not capable of growth and binary fission. They reproduce by reproducing their proteins and nucleic acid in the host cell, followed by the assembly of a viral particle.

Due to their characteristics, viruses are classified into a separate kingdom, Vira, which includes viruses of vertebrate and invertebrate animals, plants and protozoa. The modern classification of viruses is based on the following main criteria:

1. Type of nucleic acid (RNA or DNA), its structure (single or double stranded, linear, circular, continuous or fragmented).

2. The presence of a lipoprotein membrane (supercapsid).

3. Viral genome strategy (i.e., the transcription, translation, replication pathway used by the virus).

4. Size and morphology of the virion, type of symmetry, number of capsomeres.

5. Phenomena of genetic interactions.

6. Range of susceptible hosts.

7. Pathogenicity, including pathological changes in cells and the formation of intracellular inclusions,

8. Geographical distribution.

9. Method of transmission.

10. Antigenic properties.

Based on criteria 1 and 2, viruses are divided into subtypes and families, and based on the characteristics listed below - into genera, species, and serovars. The name of the family ends in "viridae", some families are divided into subfamilies (ending in "virinae"), genera - "vims". Human and animal viruses are distributed in 19 families: 13 RNA genomic and 6 DNA genomic. The classification and some properties of human and animal viruses are presented in table. 1.

Table 1

CLASSIFICATION AND SOME PROPERTIES OF VIRUSES

HUMAN AND ANIMALS

KINGDOM V1RA
Virus family	Nucleic acid type	Presence of a supercapsid	Virion size. nm	Typical representatives
DNA GENOMIC VIRUSES
Adenoviridae	Linear, double-stranded	-	70-90	Adenoviruses of mammals and birds
Herpesviridae	linear double-stranded	+	220	Viruses of herpes simplex, cytomegaly, chickenpox, infectious mononucleosis
Hepadnaviridae	Double-stranded, annular with a single-stranded section	+	1 45-50	Hepatitis B virus
Papovaviridae	double-stranded, ring	-	45-55	Papilloma viruses, polyomas
Poхviridae	Double-stranded with closed ends	+	130-250	Vaccinia virus, variola virus
Parvoviridae	linear, single-strand	-	18-26	Adeno-associated virus
RNA GENOMIC VIRUSES
Areoaviridae	fragmented single-stranded	+	50-300	Viruses Lassa, Machupo
Bunyaviridae	fragmented single-stranded ring	+	90-100	Viruses of hemorrhagic fevers and encephalitis
Caliciviridae	single-strand	-	20-30	Hepatitis E virus, human caliciviruses
Coronaviridae	single-stranded +RNA	+	80-130	Human coronaviruses
Orthomyxoviridae	single-stranded, fragmented - RNA	+	80-120	Influenza viruses
Paramyxoviridae	Single-stranded, linear -RNA	+	150-300	Parainfluenza, measles, mumps, PC virus
Picornaviridae	single-stranded +RNA	-	20-30	Polio, Coxsackie, ECHO, hepatitis A viruses, rhinoviruses
Reoviridae	double-stranded RNA	-	60-80	Reoviruses, rotaviruses
Retroviridae	single-stranded RNA	+	80-100	Viruses of cancer, leukemia, sarcoma, HIV
Togaviridae	single-stranded +RNA	+	30-90	Sindbis viruses. Horse Encephalitis. krasthi
Flaviviridae	single-stranded +RNA	+	30-90	Viruses of tick-borne encephalitis, yellow fever, Dengue, Japanese encephalitis, hepatitis C, G
Rhabdoviridae	single-stranded RNA	+	30-40	Rabies virus, vesicular stomatitis virus
Filoviridae	single-stranded +RNA	+	200-4000	Ebola viruses, Marburg

Morphology and ultrastructure of viruses

Based on their structure, there are 2 types of viral particles: simple and complex.

The internal structure of simple and complex viruses is similar.

The core of the virus is the viral nucleic acid, the viral genome. The viral genome can be represented by one of 4 RNA or DNA molecules: single-stranded and double-stranded RNA and DNA. Most viruses have one whole or fragmented genome, which has a linear or closed shape. Single-stranded genomes can have 2 polarities: 1) positive, when the virion nucleic acid simultaneously serves as a template for the synthesis of new genomes and acts as an mRNA; 2) negative, performing only the function of a matrix. The genome of viruses contains from 3 to 100 or more genes, which are divided into structural, encoding the synthesis of proteins that make up the virion, and regulatory, which change the metabolism of the host cell and regulate the rate of virus reproduction.

Viral enzymes are also encoded in the genome. These include: RNA-dependent RNA polymerase (transcriptase), which is found in all negative-sense RNA viruses. Poxviruses contain a DNA-dependent RNA polymerase. Retroviruses have a unique enzyme, an RNA-dependent DNA polymerase called reverse transcriptase. The genome of some viruses contains genes encoding RNases, endonucleases, and proteinases.

On the outside, the nucleic acid is covered with a protein cover - a capsid, forming a complex - a nucleocapsid (in the chemical sense - a nucleoprotein). The capsid consists of individual protein subunits - capsomers, which represent a polypeptide chain laid in a certain way, creating a symmetrical structure. If the capsomeres are arranged in a spiral, this type of capsid folding is called helical symmetry. If capsomeres are stacked along the faces of a polyhedron (12-20-hedron), this type of capsid stacking is called icosahedral symmetry

The capsid is represented by α-helical proteins capable of polymerization, which protect the genome from various influences, perform a receptor function in this group of viruses, and have antigenic properties.

Complex viruses have an outer shell, the supercapsid, located on top of the capsid. The supercapsid consists of an internal protein layer - M-protein, then a more voluminous layer of lipids and carbohydrates extracted from the cell membranes of the host cell. Virus-specific glycoproteins penetrate inside the supercapsid, forming shaped protrusions on the outside that perform a receptor function. Viruses exist in three forms:

1) virion (viral particle) - extracellular form;

2) intracellular (vegetative) virus;

3) a virus integrated with the host DNA (provirus).

Interaction of virus with cell. Reproduction (multiplication) of viruses

The process of viral reproduction can be roughly divided into 2 phases . The first phase includes 3 stages: 1) adsorption of the virus on sensitive cells; 2) penetration of the virus into the cell; 3) deproteinization of the virus . The second phase includes the stages of implementation of the viral genome: 1) transcription, 2) translation, 3) replication, 4) assembly, maturation of viral particles and 5) exit of the virus from the cell.

The interaction of a virus with a cell begins with the adsorption process, i.e., with the attachment of the virus to the cell surface.

Adsorption represents the specific binding of the virion protein (antireceptor) to the complementary structure of the cell surface - the cell receptor. According to their chemical nature, the receptors on which viruses are fixed belong to two groups: mucoprotein and lipoprotein. Influenza viruses, parainfluenza, and adenoviruses are fixed on mucoprotein receptors. Enteroviruses, herpes viruses, arboviruses are adsorbed on lipoprotein receptors of the cell. Adsorption occurs only in the presence of certain electrolytes, in particular Ca2+ ions, which neutralize excess anionic charges of the virus and cell surface and reduce electrostatic repulsion. Adsorption of viruses depends little on temperature. The initial processes of adsorption are nonspecific in nature and are the result of electrostatic interaction of positively and negatively charged structures on the surface virus and cell, and then a specific interaction occurs between the virion attachment protein and specific groups on the plasma membrane of the cell. Simple human and animal viruses contain attachment proteins as part of the capsid. In complex viruses, attachment proteins are part of the supercapsid. They can take the form of filaments (fibers in adenoviruses), or spikes, mushroom-like structures in myxo-, retro-, rhabdo- and other viruses. Initially, a single connection of the virion with the receptor occurs - such attachment is fragile - adsorption is reversible. For irreversible adsorption to occur, multiple connections must appear between the viral receptor and the cell receptor, i.e., stable multivalent attachment. The number of specific receptors on the surface of one cell is 10 4 -10 5. Receptors for some viruses, for example, arboviruses. are contained on the cells of both vertebrates and invertebrates; for other viruses only on the cells of one or more species.

Penetration of human and animal viruses into cells occurs in two ways: 1) viropexis (pinocytosis); 2) fusion of the viral supercapsid shell with the cell membrane. Bacteriophages have their own penetration mechanism, the so-called syringe, when, as a result of contraction of the protein appendage of the phage, the nucleic acid is injected into the cell.

Deproteinization of the virus, the release of the viral hemome from the viral protective shells occurs either with the help of viral enzymes or with the help of cellular enzymes. The end products of deproteinization are nucleic acids or nucleic acids associated with the internal viral protein. Then the second phase of viral reproduction takes place, leading to the synthesis of viral components.

Transcription is the rewriting of information from DNA or RNA of a virus into mRNA according to the laws of the genetic code.

Translation is the process of translating genetic information contained in mRNA into a specific sequence of amino acids.

Replication is the process of synthesis of nucleic acid molecules homologous to the viral genome.

The implementation of genetic information in DNA-containing viruses is the same as in cells:

DNA transcription mRNA translation protein

For RNA viruses with a negative genome (influenza viruses, para-influenza viruses, etc.), the genome implementation formula is as follows:

RNA transcription i-RNA translation protein

Viruses with a positive RNA genome (togaviruses, picornaviruses) lack transcription:

RNA protein translation

Retroviruses have a unique way of transmitting genetic information:

RNA reverse transcription DNA transcription mRNA translation protein

The DNA integrates with the genome of the host cell (provirus).

After the cell has accumulated viral components, the last stage of viral reproduction begins: the assembly of viral particles and the release of virions from the cell. Virions exit the cell in two ways: 1) by “exploding” the cell, as a result of which the cell is destroyed. This path is inherent in simple viruses (picorna-, reo-, papova- and adenoviruses), 2) exit from cells by budding. Inherent in viruses containing a supercapsid. With this method, the cell does not die immediately and can produce multiple viral offspring until its resources are depleted.

Virus cultivation methods

To cultivate viruses in laboratory conditions, the following living objects are used: 1) cell cultures (tissues, organs); 2) chicken embryos; 3) laboratory animals.

I. Cell cultures

The most common are single-layer cell cultures, which can be divided into 1) primary (primarily trypsinized), 2) semi-continuous (diploid) and 3) continuous.

By origin they are classified into embryonic, tumor and from adult organisms; by morphogenesis- fibroblastic, epithelial, etc.

Primary Cell cultures are cells of any human or animal tissue that have the ability to grow in the form of a monolayer on a plastic or glass surface coated with a special nutrient medium. The lifespan of such crops is limited. In each specific case, they are obtained from the tissue after mechanical grinding, treatment with proteolytic enzymes and standardization of the number of cells. Primary cultures obtained from monkey kidneys, human embryonic kidneys, human amnion, and chicken embryos are widely used for the isolation and accumulation of viruses, as well as for the production of viral vaccines.

Semi-leathered (or diploid ) cell cultures - cells of the same type, capable of withstanding up to 50-100 passages in vitro, while maintaining their original diploid set of chromosomes. Diploid strains of human embryonic fibroblasts are used both for the diagnosis of viral infections and in the production of viral vaccines.

Continuous cell lines are characterized by potential immortality and a heteroploid karyotype.

The source of transplantable lines can be primary cell cultures (for example, SOC, PES, BNK-21 - from the kidneys of one-day-old Syrian hamsters; PMS - from the kidney of a guinea pig, etc.) individual cells of which show a tendency to endless reproduction in vitro. The set of changes leading to the appearance of such features from cells is called transformation, and the cells of continuous tissue cultures are called transformed.

Another source of transplantable cell lines is malignant neoplasms. In this case, cell transformation occurs in vivo. The following lines of transplanted cells are most often used in virological practice: HeLa - obtained from cervical carcinoma; Ner-2 - from laryngeal carcinoma; Detroit-6 - from lung cancer metastasis to the bone marrow; RH - from human kidney.

To cultivate cells, nutrient media are required, which, according to their purpose, are divided into growth and supporting media. Growth media must contain more nutrients to ensure active cell proliferation to form a monolayer. Supporting media should only ensure that cells survive in an already formed monolayer during the multiplication of viruses in the cell.

Standard synthetic media, such as synthetic media 199 and Eagle's media, are widely used. Regardless of the purpose, all cell culture media are formulated using a balanced salt solution. Most often it is Hanks solution. An integral component of most growth media is animal blood serum (veal, bovine, horse), without the presence of 5-10% of which cell reproduction and monolayer formation do not occur. Serum is not included in the maintenance media.

Isolation of viruses in cell cultures and methods for their indication.

When isolating viruses from various infectious materials from a patient (blood, urine, feces, mucous discharge, organ washings), cell cultures that are most sensitive to the suspected virus are used. For infection, cultures in test tubes with a well-developed monolayer of cells are used. Before infecting the cells, the nutrient medium is removed and 0.1-0.2 ml of a suspension of the test material, pre-treated with antibiotics to destroy bacteria and fungi, is added to each test tube. After 30-60 min. After contact of the virus with cells, excess material is removed, a supporting medium is added to the test tube and left in a thermostat until signs of virus replication are detected.

An indicator of the presence of a virus in infected cell cultures can be:

1) development of specific cell degeneration - cytopathic effect of the virus (CPE), which has three main types: round or small cell degeneration; formation of multinucleated giant cells - symplasts; development of foci of cell proliferation, consisting of several layers of cells;

2) detection of intracellular inclusions located in the cytoplasm and nuclei of affected cells;

3) positive hamagglutination reaction (RHA);

4) positive hemadsorption reaction (RHAds);

5) plaque formation phenomenon: a monolayer of virus-infected cells is covered with a thin layer of agar with the addition of a neutral red indicator (background - pink). In the presence of a virus, colorless zones (“plaques”) form on the pink agar background in the cells.

6) in the absence of CPD or GA, an interference reaction can be performed: the culture under study is re-infected with the virus that causes CPD. In a positive case, there will be no CPP (the interference reaction is positive). If there was no virus in the test material, CPE is observed.

II. Isolation of viruses in chicken embryos.

For virological studies, chicken embryos 7-12 days old are used.

Before infection, the viability of the embryo is determined. During ovoscoping, living embryos are mobile and the vascular pattern is clearly visible. The boundaries of the air sac are marked with a simple pencil. Chicken embryos are infected under aseptic conditions, using sterile instruments, after pre-treating the shell above the air space with iodine and alcohol.

Methods for infecting chicken embryos can be different: applying the virus to the chorion-allantoic membrane, into the amniotic and allantoic cavities, into the yolk sac. The choice of infection method depends on the biological properties of the virus being studied.

Indication of the virus in a chicken embryo is made by the death of the embryo, a positive hemagglutination reaction on glass with allantoic or amniotic fluid, and by focal lesions (“plaques”) on the chorion-allantoic membrane.

III. Isolation of viruses in laboratory animals.

Laboratory animals can be used to isolate viruses from infectious material when more convenient systems (cell cultures or chicken embryos) cannot be used. They take mainly newborn white mice, hamsters, guinea pigs, and rat pups. Animals are infected according to the principle of virus cytotropism: pneumotropic viruses are injected intranasally, neurotropic viruses - intracerebrally, dermatotropic viruses - onto the skin.

Indication of the virus is based on the appearance of signs of disease in animals, their death, pathomorphological and pathohistological changes in tissues and organs, as well as a positive hemagglotination reaction with extracts from organs.

Viral diseases, their features

Viruses, unlike other microorganisms, cause 2 groups of diseases:

1) viral infections,

2) tumors (benign and malignant). Features of viral infections:

1. Viral infections are widespread. Their share in the structure of infectious morbidity can be 60-80%.

2. Intracellular reproduction of viruses leads to massive death of body cells.

3. Reproduction of some viruses (HIV, measles viruses, hepatitis B, C) in the cells of the immune system leads to the development of an immunodeficiency state.

4. The ability of some viruses to integrate with the cell genome (HIV, hepatitis B virus, oncogenic RNA viruses).

5. Some viruses (rubella, cytomegalovirus) have a teratogenic effect.

6. Infectious viruses can provoke the development of tumors (adenoviruses, herpes viruses, hepatitis viruses B, C, G).

7. Viruses can cause slow infections (HIV, measles, rabies, hepatitis B, herpes viruses, etc.).

8. There is no immunoprophylaxis for many viral infections.

9. Diagnosis of viral diseases is not used in every specific case due to the widespread nature of these diseases.

10.To date, there are not enough effective drugs for the treatment of viral diseases.

CLASSIFICATION OF VIRAL INFECTIONS

Cell level

Autonomous infection

Integration infection

productive

Abortive

Whole Genome Integration

Integration of part of the genome

Chronic

Acute

Neoplatic transformation

Lack of transformation

cytolytic

Noncytolytic

Body level

Focal infection

Generalized infection

Persistent

Persistent

At the cellular level, autonomous infections are distinguished if the viral genome replicates independently of the cellular one, and integrated infections if the viral genome is included in the cellular genome. Autonomous infection is divided into productive, in which infectious offspring are formed, and abortive, in which the infectious process is terminated, and new viral particles are either not formed at all or are formed in small quantities. Productive and abortive infections can be acute or chronic. Acute infection, depending on the fate of the infected cell, is divided into cytolytic and non-cytolytic. Cytolytic infection results in cell destruction, or CPD, and the virus that causes CPD is called cytopathogenic.

At the body level, viral infections are divided into 2 groups: 1) focal, when the reproduction and action of the virus manifests itself at the entrance gate; 2) generalized, in which the virus, after multiplying at the entrance gate, spreads to various organs and tissues, forming secondary foci of infection. Examples of focal infections are acute respiratory viral infections and acute respiratory infections, generalized ones are poliomyelitis, measles, smallpox.

An acute infection does not last long, is accompanied by the release of the virus into the environment, and ends with either recovery or death of the body. An acute infection may manifest itself with a number of symptoms (manifest infection), or may be asymptomatic (inapparent infection).

With prolonged interaction of the virus with the macroorganism, a persistent infection (PI) occurs. Depending on the state of the body, the same virus can cause both acute and persistent infection (measles, herpes, hepatitis B, C viruses, adenoviruses). Clinical manifestations of PI can be pronounced, mild, or absent altogether; the virus can be released into the environment or not. Based on these characteristics, PIs are divided into latent (hidden infections, without virus isolation, caused by oncogenic viruses, HIV, herpes and adenoviruses); chronic (characterized by periods of remissions and exacerbations when the virus is released into the environment. Examples of chronic infections are herpes, adenovirus, chronic form of hepatitis B and C, etc.); slow (characterized by a long incubation period, slow development of symptoms leading to severe impairment of body functions and death).

Etiology of slow infections

Slow infections affecting humans and animals can be divided into 2 groups according to etiology:

Group I are slow infections caused by prions. Prions are protein infectious particles, have the form of fibrils, length from 50 to 500 nm, weighing 30 kDa. They do not contain nucleic acid, are resistant to proteases, heat, ultraviolet radiation, ultrasound and ionizing radiation. Prions are capable of reproduction and accumulation in the affected organ to gigantic levels, and do not cause CPE, immune response or inflammatory reactions. Degenerative tissue damage.

Prions cause diseases in humans:

1) Kuru (“laughing death”) is a slow infection endemic to New Guinea. It is characterized by ataxia and tremor with gradual complete loss of motor activity, dysarthria and death one year after the onset of clinical symptoms.

2) Creutzfeldt-Jakob disease, characterized by progressive dementia (dementia) and symptoms of damage to the pyramidal and extrapyramidal tracts.

3) Amyotrophic leukospongiosis, characterized by degenerative destruction of nerve cells, as a result of which the brain acquires a spongy (spongioform) structure.

Prion diseases in animals:

1) Bovine spongiform encephalopathy (mad cows);

2) Scrapie - subacute transmissible spongiform encephalopathy of Aries.

Group II are slow infections caused by classical viruses.

Slow viral infections of humans include: HIV infection - AIDS (causes HIV, family Retrovoridae); PSPE - subacute sclerosing panencephalitis (measles virus, family Paramyxoviridae); progressive congenital rubella (rubella virus, family Togaviridae); chronic hepatitis B (hepatitis B virus, family Hepadnaviridae); cytomegalovirus brain damage (cytomegaly virus, family Herpesviridae); T-cell lymphoma (HTLV-I, HTLV-II, family Retroviridae); subacute herpetic encephalitis (herpes simples, family Herpesviridae), etc.

In addition to slow infections caused by viruses and prions, there is a group of nosological forms that, in clinical practice and outcome, correspond to the signs of a slow infection, but precise data on the etiology are not yet available. Such diseases include multiple sclerosis, amyotrophic lateral sclerosis, atherosclerosis, schizophrenia, etc.

Laboratory diagnosis of viral infections

The laboratory diagnosis of viral infections is based on 3 groups of methods:

1 group- Detection of the pathogen or its components directly in clinical material taken from the patient, and obtaining an answer within a few hours (fast; express diagnostics). Express diagnostic methods for the most common viral infections are given in Table. 2.

table 2

METHODS FOR EXPRESS DIAGNOSTICS OF COMMON

VIRAL INFECTIONS

Viruses	Infection	Material for research	Timing of material collection	Express diagnostic methods
Adenoviruses	Adenovirus infection	Nasopharyngeal discharge, conjunctiva, blood, feces, urine	First 7 days of illness	IF, molecular hybridization (MG), EM, ELISA, RIA
Parainfluenza, PC virus	ARVI	Nasopharyngeal discharge	The first 3-5 days of illness	IF. ELISA
Flu	Flu	Nasopharyngeal discharge	The first 3-5 days of illness	IF, IFA, RIA, EM
Rhinoviruses	ARVI	Nasopharyngeal discharge	The first 3-5 days of illness	IF
Herpes simplex	Herpes simplex	Vesicle contents	During the first 12 days after the rash appears	IF, MG, IEM, IFA
Chickenpox and herpes zoster	Chicken pox, herpes zoster	Vesicle contents	During the first 7 days after the rash appears	ELISA, IF, IEM
Cytomegaly	Cytomegalovirus infection	Urine, saliva, blood	Throughout the entire period of the disease	EM, microscopy of stained fingerprint smears, MG, IF, IgM detection
Rotaviruses	Acute gastroenteritis	Feces	The first 3-5 days of illness	EM, IEM, ELISA, RIA, MG, RNA electrophoresis in PAGE
Hepatitis A	Hepatitis A	Feces, blood	The first 7-10 days of illness	IEM, ELISA, RIA, IgM detection
Hepatitis B	Hepatitis B	Blood	The entire period of the disease	ELISA, RIA, ROPGA, MG, PCR, VIEF

2nd group methods - Isolation of the virus from clinical material, its indication and identification (virological diagnostics).

In most cases, the concentration of virus in clinical material is insufficient for rapid detection of the virus or its antigens. In these cases, virological diagnostics are used. This group of methods requires a long time, is labor-intensive, and is often retrospective. However, virological diagnosis is necessary for infections caused by new types of virus, or when diagnosis cannot be made by other methods.

For virological diagnosis, the doctor must ensure that the necessary samples of material are taken at the appropriate phase of the disease, delivered to the laboratory, providing the diagnostic laboratories with the necessary clinical information.

The material for virological research in diseases accompanied by diarrhea or other gastrointestinal disorders suggesting a viral etiology is fresh portions of feces. For diseases of the respiratory system, material for research is best obtained by aspiration of mucus and washings. Nasopharyngeal swabs are less informative. In the presence of a vesicular rash, the material for examination is the liquid aspirated from the vesicles with a needle. For petechial and maculopapular rashes, the material for research is both mucus samples from the nasopharynx and feces. If neuroviral infections are suspected, mucus from the nasopharynx, feces and cerebrospinal fluid should be collected for virological testing. The material used to diagnose mumps and rabies is saliva. If cytomegalovirus and papovirus infections are suspected, the material may be urine. An attempt to isolate the virus from the blood can be made if infections caused by certain arboviruses and herpes viruses are suspected. A brain biopsy can be performed to diagnose herpetic encephalitis, SSPE, progressive rubella panencephalitis, Kreptzfeldt-Jakob disease, leukospongiosis, etc.

Preparations of mucus from the nasopharynx or feces are placed in a transport medium consisting of saline solution with added antibiotics and a small amount of protein or animal serum. Materials can be stored at 4°C for no more than 48 hours. Longer storage requires a temperature of -70°C.

Isolation of the virus from clinical material is carried out by inoculating it into cell cultures, embryos, or infecting laboratory animals with it (see Cultivation of viruses).

Influenza virus should be isolated by inoculating virus-containing material into the ampiotic or allantoic cavity of the chick embryo. To isolate the Coxsackie A virus, rabies virus, many arboviruses, and areiaviruses, iptraperitoneal and intraperitoneal inoculation of material into newborn mice is recommended.

After infection of a cell culture, the latter is examined for the presence of CDD. Many enterovnrus cause early CDD (within a few hours). Cygomegaloviruses, adenoviruses, and rubella virus cause CPE within a few weeks, and sometimes it is necessary to resort to obtaining a subculture. The presence of sinusitis indicates the presence of viruses such as PC, measles, mumps, and herpes viruses.

Identification of viruses isolated in these systems is carried out using serological methods. Serological reactions such as RTGL, RN, PIT Ade are used only for viral infections. RSK, RPGA, ELISA, RIA, IF, RP, etc. are used to diagnose both viral infections and infections caused by other pathogens.

Diagnostics of ARVI and intestinal infections are presented in Schemes 2 and 3.

ISOLATION OF VIRUSES FROM NASOPHARYNX DISCHARGE, THEIR INDICATION AND IDENTIFICATION IN RESPIRATORY INFECTIONS

VIRAL INFECTIONS

Nasopharyngeal mucus treated with antibiotics

Chick embryo infection

Infection of suckling mice

Paralysis, death

Death, specific lesions of CAO

Coxsackie viruses, herpes

RSK, RTGA

Influenza viruses

Herpes viruses

Infection of cell culture

CPP may be absent

Syncytia education

Herpetic type of CPD

Adenoviral type of CPD

Picornaviral type of CPD

RSK, RN according to color test

IF, RN, RSK, RTGA

IF, RN, RSK

Interference

IF, RN, RTGA, RTGAds

Adenovirs

Enteroviruses, rhinoviruses

Herpes simplex viruses, cytomegaly

RS virus, measles, parainfluenza

Influenza viruses, parainfluenza, EP

Rubella virus

3 group methods - Serological diagnosis of viral infections.

A single serological test only in rare cases makes it possible to diagnose a viral disease (for example, with HIV infection). In most cases, serological diagnosis requires paired sera taken in the acute phase of the disease and 2-4 weeks later. The detection of a fourfold or more increase in antibody titer is usually considered as a diagnostic sign of an acute viral infection.

ISOLATION OF VIRUSES FROM FECES, THEIR INDICATION AND IDENTIFICATION IN INTESTINAL VIRAL INFECTIONS

Fecal suspension, treated with antibiotics, clarified by centrifugation

Infection of mice

Infection of cell cultures

Paralysis, death

Picornoviral type of CPD

Reoviral type of CPD

Adenoviral type of CPD

RN, RSK

RSK, RN according to color test

IF, RN, RTGA

RTGA, RSK, RN

Coxsackie A, B, rotaviruses

enteroviruses

Adenoviruses

Rotaviruses

Principles of therapy and prevention of viral infections

1 group- Abnormal nucleosides - analogues of nucleic acid metabolism precursors, inhibit the functions of viral polymerases or are included in the nucleic acid chain, making it non-functional.

A pyrimidine analogue, iododeoxyuridine, is used to treat herpetic keratitis, cutaneous herpes and cytomegaly. Purine analogues - vidorabide - are used to treat herpetic encephalitis, chickenpox and herpes zoster. Acyclovir (Zovirax) is also used to treat various types of herpetic infections. Ribovirin (virazol) is effective against RNA and DNA viruses. For the treatment of HIV infection, nucleoside analogs have been obtained that inhibit HIV reverse transcriptase, azidothymidine (zidovudine), timazide (phosphatide), hivid (zalcitabine).

2nd group adamantaneamine hydrochloride derivatives. Drugs: amantadine and rimantadine inhibit the reproduction of influenza, measles, red viruses

Nuhn. Most effective against influenza A. Mechanism of action: disruption of virus deproteinization.

3 group- thiosemicarbazoics. The drug metisazoi (marborap) is active against variola viruses. The mechanism of action of the drug is to suppress the synthesis of viral proteins and the assembly of viral particles.

4 group inhibitors of proteolytic activity of viruses. The essence of this phenomenon is that many proteins of picoria-, ortho-, adeno-, toga-, and retroviruses acquire viral activity only after cutting these proteins into fragments by protease enzymes. Protease inhibitors such as Gorlox, Contrical, and s-aminocaproic acid are used to treat infections caused by these viruses. In our republic, a drug from this group, invirase (saqunnavir), is used to treat HIV infection.

5 group. One of the new and promising areas of chemotherapy is the creation of drugs such as “nucleases” that can damage viral genes, which will make it possible to treat integration viral diseases.

6 group interferons. Currently, α-interferon (leukocyte IF) is used for both treatment and prevention, especially of respiratory viral infections. The mechanism of action is a violation of the synthesis of viral proteins. β-interferon or immune interferon is widely used. -interferon enhances the function of T-killers and natural killers, T-effectors of HRT. Used to treat malignant tumors and viral infections.

7 group- virus-specific immunoglobulins. which are obtained from the blood of convalescents or specially vaccinated donors. They are used to prevent measles, hepatitis A, B, influenza, parainfluenza and other viral infections (anti-rabies immunoglobudin obtained from the blood of immunized animals is used to prevent rabies). Igs interfere with virions and prevent virus adsorption on sensitive cells.

8 group- Vaccines. To prevent a number of viral infections, killed vaccines containing viruses inactivated with formalin or β-cropnolactone (vaccine against influenza, measles, polio, Japanese and tick-borne encephalitis, rabies), live (attenuated) virus vaccines containing viruses with weakened virulence ( vaccine against influenza, measles, mumps, rubella, polio, rabies, yellow fever, etc.); subunit vaccines containing viral protective antigens (subunits) (influenza vaccine); recombinant (genetically engineered) vaccines (a vaccine against hepatitis B, for the production of which the gene encoding the HBs antigen is introduced into the genome of a yeast cell). Synthetic vaccines are under development.

Laboratory diagnosis of viral hepatitis

Currently, in the category of viral hepatitis, 7 independent nosological forms are considered: hepatitis A, B, C, D, E, F, G. According to the route of transmission, viral hepatitis is divided into:

1. Enteral, transmitted by the fecal-oral route. These include hepatitis A, E and, obviously, F.

2. Parenteral, transmitted through parenteral manipulation, including, under natural conditions, transplacental and sexual transmission. These include hepatitis B, C, D, G.

The most widespread are hepatitis A, B, C, the comparative characteristics of which are presented in table. 3.

Table 3

COMPARATIVE CHARACTERISTICS

VIRAL HEPATITIS A, B, C

Sign	Hepatitis A	Hepatitis B	Hepatitis C
Virus (family)	Picomaviridae	Hepadnaviridae	Flaviviridae
Nucleic acid type	single-stranded +RNA	double-stranded DNA with a single-stranded region	single-stranded +RNA
Virion size	27-32 nm	42-45 nm	30-60 nm
Supercapsid	absent	available	available
Path of infection	fecal-oral	parenteral	parenteral
Incubation period	on average 25-30 days	on average 60-90 days, maybe up to 6 months	on average 35-70 days
Age groups	mainly children under 1 5 years old	children and adults	children and adults
Seasonality	mostly August-September	during the whole year	during the whole Gogi
Transition to chronic form	absent	occurs	takes place in 50% of cases
Carriage	absent	long-term	long-term
Oncogenicity	absent	occurs	occurs

I. Hepatitis A (hA). Laboratory diagnosis of hepatitis A is based either on identifying the pathogen itself (immune electron microscopy method - IEM), its antigens (radioimmune, enzyme immunoassay, immunofluorescent method - RIA, ELISA, IF) or antibodies to the hepatitis A virus (RIA, ELISA).

For early diagnosis of the disease, as well as identifying sources of infection, the determination of the antigen of the hepatitis A virus in the feces of patients is used, where it appears 7-10 days before clinical symptoms and in the first days of the disease.

Of the currently determined specific markers of hepatitis A, the most important are Ig M antibodies to the hepatitis A virus, which appear in the blood serum and saliva at the onset of the disease and persist for 3-6 months. The detection of Ig M class antibodies to the hepatitis A virus clearly indicates hepatitis A and is used to diagnose the disease, including asymptomatic cases of infection, and to identify sources of infection in foci.

Antibodies to the hepatitis A virus of the Ig G class are detected from the 3-4th week of the disease and persist for a long time, which makes it possible to assess the state of the population’s immunity and the dynamics of specific humoral immunity.

Hepatitis A virus in material from a patient can be detected by immune electron microscopy. The method is based on mixing a virus suspension with antiserum, separating immune complexes and examining them in an electron microscope.

II.Hepatitis B (hB). In the body of people infected with the hepatitis B virus, serological markers can be detected at different frequencies and at different stages: surface HBs Ag and core HBe Ag, as well as antibodies to them (anti-HBc, anti-HBe, anti-HBs). The dynamics of their appearance and interpretation of the results are presented in Table. 4 and 5.

Table 4

SEROLOGICAL MARKERS IN HEPATITIS B

Table 5

INTERPRETATION OF SEROLOGICAL MARKERS IN HEPATITIS B

Antigens		Antibodies to HBs-Ar	Antibodies kNVs-Ag		Interpretation
BHs	НВе		fgG	IgM
+	+	–	–	+	Acute phase of hepatitis
+	±	–	+	–	Chronic hepatitis B
+	–	–	–	–	Carriage
–	–	+	–	–	Hepatitis B in the past
–	–	–	–	–	No history of hepatitis B

All antigens and their corresponding antibodies can serve as indicators of the infectious process.

The presence of viral DNA, HBs Ag, HBe Ag and anti-HBc class Ig M indicates an acute period of infection. During the period of convalescence, these are anti-HBc antibodies of the Ig G class and they are detected together with anti-Hbs antibodies. The prolonged presence of HBs-Ag, HBe-Ag and anti-HBc (IgG) in the blood is an unfavorable sign indicating the formation of a chronic process.

During the formation of long-term carriage, HBs Ag is constantly determined. To detect antigens and antibodies, RPGA, RIA and ELISA are used. To detect HBs Ag, ROPHA is used - a reverse passive hemagglutination reaction with a mandatory positive control for HBs Ag.

III. Hepatitis C (hC).Caused by an RNA virus that belongs to the Flaviviridae family. The diameter of virions is 30-60 nm, sensitive to treatment with chloroform. Positive single-stranded RNA encodes the synthesis of three structural and five non-structural proteins. Hepatitis C is similar in clinical and biochemical characteristics to hepatitis B. In 60% of infected individuals, the disease becomes chronic, and 20% of chronic patients develop cirrhosis of the liver. The mechanism of transmission of the hepatitis C virus is mainly parenteral. Laboratory diagnosis of hepatitis C is based on the determination of antibodies to the hepatitis virus using ELISA or RIA methods.

IV. The causative agent of hepatitis delta (hepatitis D).An RNA-containing, defective virus that can resolve itself in the host’s body only with the obligatory participation of a helper virus, the role of which is played by the hepatitis B virus. The envelope of the delta virus is formed by HBs Ag. The addition of delta infection to hepatitis B leads to the development of severe malignant forms of the disease, chronic forms of the disease with the early formation of liver cirrhosis.

Laboratory diagnosis of hepatitis D is carried out by detecting markers of the hepatitis B virus and delta virus infection, HBs Ag, anti-HBc (Ig M) and delta Ag. The latter are tested using ELISA and RIA. Anti-delta Ig M, which are detected throughout the disease, are of greatest diagnostic importance.

V. Hepatitis E. Widely distributed in tropical and subtropical countries, the spread of the disease occurs by water. The virion with a diameter of 27-32 mm contains single-stranded RNA, and its physicochemical properties are similar to viruses of the Calicivmdae family. Laboratory diagnosis is based on the determination of AT in blood serum by ELISA.

VI. Hepatitis G. The hepatitis G virus was discovered in 1995, classified in the Flaviviridae family, transmitted parenterally. The size of the virion is 20-30 nm. The genome of the virus is represented by single-stranded + RNA. The capsid protein is defective or not synthesized at all. Therefore, it is assumed that the hepatitis G virus uses either proteins from undiscovered viruses or cellular proteins for its capsid. There are indications of the presence of a lipid membrane in the virus. The marker of virus replication is its RNA. Antibodies against the E 2 protein of the hepatitis G virus are detected only in the absence of viral RNA. This indicates that, unlike hepatitis C, detection of antibodies in hepatitis G cannot be used to search for virus carriers, but is suitable for registering a past infection.

VII. Hepatitis F. The hepatitis F virus was discovered by French scientists and has not actually been studied.

Laboratory diagnosis of HIV infection

When diagnosing HIV infection, 4 groups of methods are used:

1. Determination of the presence of the virus, its antigens or RNA copies in materials from a patient or HIV-infected person

2. Serological diagnosis, based on the detection of specific antibodies to surface (gp 120 and gp 41) and internal (p 18 and p 24) HIV proteins.

3. Identification of pathognomonic (specific) changes in the immune system for HIV infection.

4. Laboratory diagnosis of opportunistic infections (AIDS-associated diseases).

1. Virological diagnosis. The material for isolating HIV is blood T-lymphocytes, bone marrow leukocytes, lymph nodes, brain tissue, saliva, sperm, cerebrospinal fluid, and blood plasma. The resulting material is used to infect a continuous culture of T-lymphocytes (H9). Indication of HIV in cell culture is carried out by CPD (formation of symplasts), as well as by immunofluorescence, electron microscopy, and expressed reverse transcriptase activity. Modern research methods make it possible to detect one infected lymphocyte per 1000 cells.

Detection of viral antigens in infected T lymphocytes is carried out using monoclonal antibodies

In recent years, determining the number of copies of HIV RNA in the blood plasma using the polymerase chain reaction (PCR) method - the so-called viral load - has been crucial for determining the prognosis and severity of HIV infection. If in patients not receiving therapy, the viral load is below the detection limit (less than 5000 copies of HIV RNA in 1 ml of plasma), this indicates the absence of progression or slow progression. The degree of contagion is minimal. A high viral load (more than 10,000 copies of RNA in 1 ml of plasma) in patients with a number of CO4 lymphocytes less than 300 in 1 μl always indicates progression of the disease.

2. Serological diagnosis. Currently it is most widespread.

Material for research: 5 ml. heparinized blood, which can be stored refrigerated, but not frozen, for 6-8 hours before delivery to the laboratory.

For the purpose of serological diagnosis of AIDS, primarily enzyme immunoassay methods with standard enzyme immunoassay systems (ELISA) are used. This is a screening method. The operating principle is based on the classic principle of direct ELISA. The immunosorbent is polystyrene tablets with immobilized inactivated virus-specific antigen obtained from HIV or synthetically. Then the diluted test serum is added. Incubation is carried out in wells with antigen. After the binding of AG to AT, unbound proteins are washed three times, and then a conjugate of antibodies to human immunoglobulins with an enzyme label is added to the wells. The formation of a specific AG+AT complex is detected by adding a substrate for the enzyme (a solution of orthophenylenediamine and hydrogen peroxide). As a result, the color of the medium changes in proportion to the amount of antibodies. The results of the study are taken into account on a spectrophotometer. Blood sera that have virus-specific antibodies according to ELISA data must be further examined by immunoblotting.

Immune blotting is a confirmatory test because it detects antibodies to various HIV proteins. It is based on preliminary fractionation by molecular weight (separation) of HIV proteins by electrophoresis in a polyacrylamide gel, followed by transfer of antigens to a nitrocellulose membrane. The test serum is then applied to the membrane. In this case, specific antibodies form a complex with a specific antigen (gp.120, gp.41, p.24, p.18). The final stage of the study is the identification of antibodies to various HIV proteins. To do this, antibodies against human proteins labeled with an enzyme or radioisotope label are added to the system. Thus, virus-specific antibodies to all or most HIV antigens are detected (or not detected) in the patient’s serum.

3. Studies of immune status. Aimed at identifying:

1) reducing the ratio of CD4/CD8 cells (in N 2 and >, with AIDS - 0.5 and
2) reducing the content of CD4 cells (
3) the presence of one of the laboratory signs, including anemia, leukopenia, thrombopenia, lymphopenia;

4) increasing the concentration of Ig A and Ig G in the blood serum;

5) reducing the response of lymphocyte blast formation to mitogens;

6) absence of skin reaction of GTZ to several antigens;

7) increasing the level of circulating immune complexes.

DEVELOPMENT OF TUMORS, OPPORTUNISTIC INFECTIONS AND INVASIONS IN HIV INFECTION

CNS cells

T helper cells

Encephalopathy dementia

Violation of GMOs and CIOs

Dysfunction of T-killer cells

Ontogenesis

Kaposi's sarcoma, brain lymphoma

Opportunistic infections, infestations caused by

Viruses

The simplest

Bacteria

Helminths

• 
  Herpes simplex type I and II;
• 
  Herpes zoster;
• 
  Cytomegalovirus;
• 
  Epstein-Barr virus;