Discovery of the value of the properties of viruses. By whom and when were viruses discovered? History of virology discovery of viruses. Scientific virological institutions. Virus life cycle and further research

Pukhaeva Varvara Sergeevea

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Project on the topic: “The history of the discovery of non-cellular life”

Purpose of the work: to study the history of the discovery of viruses and the prospects for their use in modern science Objectives: to study the contribution of scientists to the development of virology; find out the nature of viral particles, their effect on organisms and methods of combating them; explore areas and prospects for the use of viruses by humans.

Discovery of viruses: Russian scientist-researcher. In 1892, having described the unusual properties of the causative agents of tobacco disease - tobacco mosaic, which passed through bacterial filters, he suggested the existence of a special form of life - “filterable bacteria”, which were later called “viruses”. Dmitry Iosifovich Ivanovsky (1864 – 1920)

Structure of the virus Bacteriophage

CLASSIFICATION OF VIRUSES DEOXYVIRUSES RIBOVIRUSES 1. Double-stranded DNA 2. Single-stranded DNA 1. Double-stranded RNA 2. Single-stranded RNA 1.1. Cubic type of symmetry: 1.1.1. Without outer shells: (adenoviruses) 1.1.2. With outer shells: (herpes viruses) 1.2. Mixed type of symmetry: (T-even bacteriophages) 1.3. Without a specific type of symmetry: (smallpox viruses) 2.1. Cubic type of symmetry: 2.1.1. Without outer membranes: (Kilham rat virus, adenosatellites) 1.1. Cubic type of symmetry: 1.1.1. Without outer shells: (reoviruses, plant wound tumor viruses) 2.1. Cubic type of symmetry: 2.1.1. Without outer shells: (poliomyelitis virus, enteroviruses, rhinoviruses) 2.2. Spiral type of symmetry: 2.2.1. Without outer shells: (tobacco mosaic virus) 2.2.2. With outer shells: (influenza viruses, rabies viruses, oncogenic RNA viruses)

Discovery of antiviral vaccines Edward Jenner (1749 - 1823), in 1796, discovered a vaccine against smallpox Louis Pasteur (1822–1895), in 1886 Discovered a vaccine against rabies

The use of viruses in modern science: 1. Some phages (alone or in combination with antibiotics) were used for the prevention (phage prophylaxis) and treatment (phage therapy) of a number of human bacterial infectious diseases (dysentery, typhoid fever, cholera, plague, staphylococcal and anaerobic infections, etc. .) and animals.

Application of viruses in modern science: 2. Application of virus interference for the treatment of a number of viral diseases of humans and animals (based on the production of interferon)

The use of viruses in modern science: 3. The use of the Rigvir virus, capable of destroying malignant tumors and having unique immunoactivating properties, in oncology (unique methods of the Latvian Virotherapy Center) Latvian Virotherapy Center

The use of viruses in modern science: 4. The use of viruses to control insect pests Caterpillars Sawfly beetle

The use of viruses in modern science: 5. The use of viruses to control the number of pest animals (using the example of rabbits in Australia)

The use of viruses in modern science: 6. The use of the ability of viruses for horizontal gene transfer between two unrelated (belonging to different species or even kingdoms) individuals in genetic engineering in the creation of genetic vectors and the breeding of genetically modified organisms Genetically modified mouse with enhanced muscles

The use of viruses in modern science: 7. Viruses are used in the breeding of plants and domestic animals Tulips infected with a virus

Varieties of phlox created by infection with viruses The use of viruses in modern science:

Thank you for your attention!

Question 1. Who discovered viruses? How do viruses work?

The virus (the causative agent of tobacco disease - tobacco mosaic) was first described in 1892 by the Russian scientist D.I. Ivanovsky.

Every virus is made up of nucleic acid (RNA or DNA) and protein. Nucleic acid is the genetic material of the virus; it is surrounded by a protective shell - the capsid. The capsid consists of protein molecules and has a high degree of symmetry, usually having a helical or polyhedral shape. In addition to the nucleic acid, the virus’s own enzymes may be located inside the capsid. Some viruses (for example, influenza virus and HIV) have an additional envelope formed from the host cell membrane.

Question 2. What is the role of viruses in nature?

Question 4. Give examples of diseases caused by viruses. Do you think it is possible to protect a person from viral infections? What should you do for this?

Examples of diseases caused by viruses are hepatitis A, hepatitis B, AIDS, influenza, herpes, etc.

To protect yourself from viruses, you must follow these rules:

1. Provide your body with environmental safety: drink good quality water, try to avoid getting heavy metal salts, radionuclides, pesticides, nitrates and other poisons into your body. All this negatively affects the immune system.

2. Remember the rules of a nutritious diet. Periodically consume foods that have antibacterial and antiviral activity, this will strengthen your immune system.

3. Do not allow diseases to become chronic, since long-term disruptions in the functioning of any organs lead to constant stress and decreased immunity.

4. Give up bad habits. Smoking and alcohol, as well as prolonged lack of sleep will inevitably lead to disruptions in the immune system.

5. Regulate the level of mental and physical stress. Constant stress and overwork undermine your strength.

6. Do not take medications without good reason and a doctor's recommendation.

This applies not only to immunostimulating drugs. Almost all pharmaceuticals affect the immune system in one way or another. Even seemingly harmless preparations of bifidobacteria, when taken for a long time, can cause a weakening of protective mechanisms.

Question 5. What is a bacteriophage?

A bacteriophage is a virus that infects bacteria.

Question 6. Can a virus exist outside a cell?

Viruses can exhibit the properties of living organisms only in cells.

Question 7. How do viruses reproduce?

Viruses need a cell to reproduce. Having penetrated the cell, the virus integrates its nucleic acid, which carries hereditary information about it, into the chromosome of the host cell and thus “forces” it to work according to its program - to synthesize the components of viral particles. The accumulation of viral particles leads to their exit from the cell. For some viruses, this occurs due to an “explosion,” as a result of 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 body's cells can remain alive for a long time.

Abstract on biology

Topic: Viruses.

Man encounters viruses, first of all, as the causative agents of the most common diseases that affect all life on Earth: people, animals, plants and even single-celled organisms - bacteria, fungi, protozoa. The share of viral infections in human infectious pathology has increased sharply – it has reached almost 80%. This is due to at least three reasons:

First, there are successful measures to combat infections of other origins (for example, highly effective antibiotics for bacterial infections), and against this background the ratio between viral and bacterial infections has changed significantly;

Secondly, the absolute number of diseases with some viral infections (for example, viral hepatitis) has increased;

Thirdly, new methods for diagnosing viral infections are being developed and existing ones are being improved, and their sensitivity threshold is increasing.

As a result, new infections were “discovered”, which, of course, existed before, but remained unrecognized.

I. History of discovery and methods for studying viruses

Figure 1. – Ivanovsky D.I.

In 1852, Russian botanist D.I. Ivanovsky was the first to obtain an infectious extract from tobacco plants affected by mosaic disease. When such an extract was passed through a filter capable of retaining bacteria, the filtered liquid still retained infectious properties. In 1898, the Dutchman Beijerinck coined the new word virus to describe the infectious nature of certain filtered plant liquids. Although significant advances had been made in obtaining highly purified samples of viruses and the chemical nature of the viruses had been determined to be nucleoproteins, the particles themselves remained elusive and mysterious because they were too small to be seen with a light microscope. That is why viruses were among the first biological structures that were examined in an electron microscope immediately after its invention in the 30s of our century.

Five years later, while studying diseases of cattle, namely foot and mouth disease, a similar filterable microorganism was isolated. And in 1898, when reproducing the experiments of D. Ivanovsky by the Dutch botanist M. Beijerinck, he called such microorganisms “filterable viruses.” In abbreviated form, this name began to denote this group of microorganisms.

In 1901, the first human viral disease was discovered - yellow fever. This discovery was made by the American military surgeon W. Reed and his colleagues.

In 1911, Francis Rous proved the viral nature of cancer - Rous sarcoma (only in 1966, 55 years later, he was awarded the Nobel Prize in Physiology or Medicine for this discovery).

Hershey's experiment. The experiment was carried out on bacteriophage T2, the structure of which had by that time been elucidated using electron microscopy. It turned out that the bacteriophage consists of a protein shell, inside of which there is DNA. The experiment was planned in such a way as to find out what - protein or DNA - is the carrier of hereditary information.

Hershey and Chase grew two groups of bacteria: one in a medium containing radioactive phosphorus-32 in the phosphate ion, the other in a medium containing radioactive sulfur-35 in the sulfate ion. Bacteriophages, added to the environment with bacteria and multiplying in them, absorbed these radioactive isotopes, which served as markers when building their DNA and proteins. Phosphorus is contained in DNA, but is absent from proteins, and sulfur, on the contrary, is contained in proteins (more precisely, in two amino acids: cysteine ​​and methionine), but is not in DNA. Thus, some bacteriophages contained sulfur-labeled proteins, while others contained phosphorus-labeled DNA.

Once radiolabeled bacteriophages were isolated, they were added to a culture of fresh (isotope-free) bacteria and the bacteriophages were allowed to infect these bacteria. After this, the medium containing the bacteria was vigorously shaken in a special mixer (this has been shown to separate the phage membranes from the surface of the bacterial cells), and then the infected bacteria were separated from the medium. When bacteriophages labeled with phosphorus-32 were added to bacteria in the first experiment, it turned out that the radioactive label was in the bacterial cells. When, in the second experiment, bacteriophages labeled with sulfur-35 were added to the bacteria, the label was found in the fraction of the medium with protein shells, but it was not present in the bacterial cells. This confirmed that the material that infected the bacteria was DNA. Since complete virus particles containing viral proteins are formed inside infected bacteria, this experiment was considered one of the decisive proofs of the fact that genetic information (information about the structure of proteins) is contained in DNA.

In 1969, Alfred Hershey received the Nobel Prize for his discoveries of the genetic structure of viruses.

In 2002, the first synthetic virus was created at New York University.

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.

History of virology It 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.

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).

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.

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.

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 genetics of bacteriophages 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, named 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.

In this article we will talk about the history of the discovery of viruses. This is an interesting topic that does not receive much attention in the modern world, but in vain. First, we will understand what the virus itself is, and then we will talk about other aspects of this issue.

Virus

A virus is a noncellular infectious organism that can only reproduce inside living cells. By the way, from Latin this word is translated literally as “poison”. These formations can affect all types of living organisms, from plants to bacteria. There are also viruses that can only reproduce within their other counterparts.

Study

Research began in 1892. Then Dmitry Ivanovsky published his article in which he described a pathogen of tobacco plants. The virus was discovered by Martin Beijerinck in 1898. Since then, scientists have described about 6,000 different viruses, although they believe that there are more than 100 million of them. Note that these formations are the most numerous biological form that is present in any ecosystem on Earth. They are studied by virology, namely the branch of microbiology.

Short description

Note that while the virus is outside the cell or in the process of nucleation, it is an independent particle. Typically consists of three components. The first is genetic material, which is represented by DNA or RNA. Note that some viruses may have two types of molecules. The second component is the protein shell, which protects the virus itself and its lipid shell. By its presence, viruses are distinguished from similar infectious bacteria. Depending on the type of nucleic acid, which is essentially genetic material, viruses are divided into DNA-containing and RNA-containing viruses. Previously, prions were classified as viruses, but then it turned out that this was an erroneous opinion - these are ordinary pathogens that consist of infectious material and do not contain nucleic acids. The shape of the virus can be very diverse: from spiral to much more complex structures. The size of these formations is approximately one hundredth of a bacterium. However, most viruses are so small that they cannot be clearly seen even with a light microscope.

Life form

Appearance

The history of the discovery of the virus is silent about how they appeared on the evolutionary tree. This is indeed a very interesting question that has not yet been sufficiently studied. It is believed that some viruses could have been formed from small DNA molecules that could be transmitted between cells. There is another possibility that viruses originated from bacteria. Moreover, due to their evolution, they are an important element in horizontal gene transfer and provide genetic diversity. Some scientists consider such formations to be a distinctive form of life due to certain characteristics. First, there is the genetic material, the ability to reproduce and evolve naturally. But at the same time, viruses do not have very important characteristics of living organisms, for example, cellular structure, which is the main property of all living things. Due to the fact that viruses have only part of the characteristics of life, they are classified as forms that exist on the edge of life.

Spreading

Viruses can spread in different ways; there are many different ways. They can be transmitted from plant to plant by insects that feed on plant juices. An example is aphids. In animals, viruses can be spread by blood-sucking insects that carry bacteria. As we know, the influenza virus spreads in the air through sneezing and coughing. For example, rotavirus and norovirus can be transmitted through contact with contaminated food or liquid, that is, through the fecal-oral route. HIV is one of the few viruses that can be transmitted through blood transfusions and sexual contact.

Each new virus has certain specificity in relation to its hosts. In this case, the host range can be narrow or wide, depending on how many cells were affected. Animals respond to infection with an immune response that destroys pathogenic organisms. Viruses as a form of life are quite adaptable, so they are not so easy to destroy. In humans, the immune response can be a vaccine against specific infections. However, some organisms can bypass a person's internal security system and cause chronic disease. These are the human immunodeficiency virus and various hepatitis. As is known, antibiotics cannot affect such organisms, but despite this, scientists have developed effective antiviral drugs.

Term

But before we talk about the history of the discovery of viruses, let's talk about the term itself. As we know, the word is literally translated as “poison.” It was used in 1728 to identify an organism that is capable of causing an infectious disease. Before Dmitry Ivanovsky discovered viruses, he coined the term “filterable virus,” by which he meant a pathogenic agent of a non-bacterial nature that can pass through various filters in the human body. The well-known term “virion” was coined in 1959. It means a stable viral particle that has left the cell and can independently infect further.

History of research

Viruses became something new in microbiology, but data about them accumulated gradually. Advances in science have made it clear that not all viruses are caused by pathogens, microscopic fungi, or protists. Note that researcher Louis Pasteur was never able to find the agent that causes rabies. Because of this, he assumed that it was so small that it was impossible to examine it under a microscope. In 1884, Charles Chamberlant, a famous microbiologist from France, invented a filter whose pores were much smaller than bacteria. Using this tool, you can completely remove bacteria from a liquid. In 1892, Russian microbiologist Dmitry Ivanovsky used this apparatus to study a species that was later named tobacco mosaic virus. The scientist's experiments showed that even after filtration, infectious properties are retained. He suggested that the infection could be caused by a toxin released by bacteria. However, then the man did not develop this idea further. At that time, the ideas were popular that any pathogen could be identified using a filter and grown in a nutrient medium. Note that this is one of the postulates of the theory of disease at the microbial level.

"Ivanovsky Crystals"

Using an optical microscope, Ivanovsky observed infected plant cells. He discovered crystal-like bodies, which are now called virus clusters. However, then this phenomenon was called “Ivanovsky crystals.” A Dutch microbiologist in 1898, Martin Beijerinck, repeated Ivanovsky's experiments. He decided that the infectious material that passes through the filter was a new form of agent. At the same time, he confirmed that they can reproduce only in dividing cells, but experiments did not reveal that they were particles. Martin then called these particles "soluble living microbes", literally speaking, and again began to use the term "virus". The scientist argued that viruses are liquid in nature, but this conclusion was refuted by Wendell Stanley, who proved that viruses are essentially particles. At the same time, Paul Frosch and Friedrich Leffler discovered the first animal virus, namely the causative agents of foot-and-mouth disease. They passed it through a similar filter.

Virus life cycle and further research

At the beginning of the last century, English bacteriologist Frederick Twort discovered a group of viruses that could multiply in bacteria. Now such organisms are called bacteriophages. At the same time, Canadian microbiologist Felix Darelle described viruses that, when in contact with bacteria, can form a space around themselves with dead cells. He made suspensions, thanks to which he was able to determine the lowest concentration of the virus at which not all bacteria die. Having made the necessary calculations, he was able to determine the initial number of viral units in the suspension.

The life cycle of the virus was actively studied at the beginning of the last century. Then it became known that these particles could have infectious properties and pass through the filter. However, they need a living host to reproduce. The first microbiologists conducted research on viruses only on plants and animals. In 1906, Ross Granville Harrison invented a unique method of growing tissue in lymph.

Breakthrough

At the same time, new viruses were being discovered. Their origin still remained and remains a mystery today. Note that the discovery of the influenza virus belongs to the American researcher Ernest Goodpasture. In 1949, a new virus was discovered. Its origin was unknown, but the organism was grown on human embryonic cells. Thus, the first poliovirus grown on living human tissue was discovered. Thanks to this, the most important polio vaccine against polio was created.

The image of viruses in microbiology appeared thanks to the invention of the electron microscope by engineers Max Knoll and Ernst Ruska. In 1935, an American biochemist conducted a study that proved that the tobacco mosaic virus consists mainly of protein. A little later, this particle was divided into protein and RNA components. It was possible to crystallize the mosaic virus and study its structure in much more detail. The first X-ray image was obtained in the late 1930s thanks to the scientists Barnal and Fankuchen. The breakthrough of virology occurred in the second half of the last century. It was then that scientists discovered more than 2,000 different types of viruses. In 1963, the hepatitis B virus was discovered by Blumberg. In 1965, the first retrovirus was described.

To summarize, I would like to say that the history of the discovery of viruses is very interesting. It allows you to understand many processes and understand them in more detail. However, it is necessary to have at least a superficial understanding in order to keep up with the times, because progress is developing by leaps and bounds.