The body of the virus has no structure. Viruses are non-cellular life forms
Viruses (biology deciphers the meaning of this term as follows) are extracellular agents that can reproduce only with the help of living cells. Moreover, they are capable of infecting not only people, plants and animals, but also bacteria. Bacterial viruses are commonly called bacteriophages. Not so long ago, species were discovered that infect each other. They are called “satellite viruses”.
General characteristics
Viruses are a very numerous biological form, as they exist in every ecosystem on planet Earth. They are studied by a science such as virology - a branch of microbiology.
Each viral particle has several components:
Genetic data (RNA or DNA);
Capsid (protein shell) - performs a protective function;
Viruses have a fairly diverse shape, ranging from the simplest spiral to icosahedral. Standard sizes are about one hundredth the size of a small bacterium. However, most specimens are so small that they are not even visible under a light microscope.
They spread in several ways: viruses living in plants travel with the help of insects feeding on grass juices; Animal viruses are carried by blood-sucking insects. They are transmitted in a large number of ways: through airborne droplets or sexual contact, as well as through blood transfusions.
Origin
Nowadays, there are three hypotheses about the origin of viruses.
You can read briefly about viruses (our knowledge base on the biology of these organisms, unfortunately, is far from perfect) in this article. Each of the theories listed above has its own disadvantages and unproven hypotheses.
Viruses as a form of life
There are two definitions of the life form of viruses. According to the first, extracellular agents are a complex of organic molecules. The second definition states that viruses are a special form of life.
Viruses (biology implies the emergence of many new types of viruses) are characterized as organisms on the border of life. They are similar to living cells in that they have their own unique set of genes and evolve based on the method of natural selection. They can also reproduce, creating copies of themselves. Since viruses are not considered by scientists as living matter.
In order to synthesize their own molecules, extracellular agents need a host cell. The lack of their own metabolism does not allow them to reproduce without outside help.
Baltimore classification of viruses
Biology describes in sufficient detail what viruses are. David Baltimore (Nobel Prize winner) developed his own classification of viruses, which is still successful. This classification based on how mRNA is produced.
Viruses must make mRNA from their own genomes. This process is necessary for the replication of its own nucleic acid and the formation of proteins.
The classification of viruses (biology takes into account their origin), according to Baltimore, is as follows:
Viruses with double-stranded DNA without RNA stage. These include mimiviruses and herpeviruses.
Single-stranded DNA with positive polarity (parvoviruses).
Double-stranded RNA (rotaviruses).
Single-stranded RNA of positive polarity. Representatives: flaviviruses, picornaviruses.
Single-stranded RNA molecule of double or negative polarity. Examples: filoviruses, orthomyxoviruses.
Single-stranded positive RNA, as well as the presence of DNA synthesis on an RNA template (HIV).
Double-stranded DNA, and the presence of DNA synthesis on an RNA template (hepatitis B).
Life period
Examples of viruses in biology are found almost at every step. But everyone’s life cycle proceeds almost the same. Without a cellular structure, they cannot reproduce by division. Therefore, they use materials located inside the cell of their host. Thus, they reproduce large numbers of copies of themselves.
The virus cycle consists of several stages that are overlapping.
At the first stage, the virus attaches, that is, it forms a specific bond between its proteins and the receptors of the host cell. Next, you need to penetrate the cell itself and transfer your genetic material to it. Some species also carry squirrels. Subsequently, loss of the capsid occurs and the genomic nucleic acid is released.
Human diseases
Each virus has a specific mechanism of action on its host. This process involves cell lysis, which leads to cell death. When dying large quantity cells, the entire body begins to function poorly. In many cases, viruses may not cause harm to human health. In medicine this is called latency. An example of such a virus is herpes. Some latent species can be beneficial. Sometimes their presence triggers an immune response against bacterial pathogens.
Some infections can be chronic or lifelong. That is, the virus develops despite the body’s protective functions.
Epidemics
Horizontal transmission is the most common type of virus spread among humanity.
The rate of transmission of the virus depends on several factors: population density, the number of people with poor immunity, as well as the quality of medicine and weather conditions.
Body protection
Types of viruses in biology that can affect human health, innumerable. The very first protective reaction is innate immunity. It consists of special mechanisms that provide nonspecific protection. This type of immunity is not able to provide reliable and long-term protection.
When vertebrates develop acquired immunity, they produce special antibodies that attach to the virus and make it safe.
However, acquired immunity is not formed against all existing viruses. For example, HIV constantly changes its amino acid sequence, so it evades the immune system.
Treatment and prevention
Viruses are a very common phenomenon in biology, so scientists have developed special vaccines containing “killer substances” for the viruses themselves. The most common and effective method The fight is vaccination, which creates immunity to infections, as well as antiviral drugs that can selectively inhibit the replication of viruses.
Biology describes viruses and bacteria mainly as harmful inhabitants human body. Currently, with the help of vaccination, it is possible to overcome more than thirty viruses that have settled in the human body, and even more in the body of animals.
Preventive measures against viral diseases should be carried out in a timely and efficient manner. For this, humanity must lead a healthy lifestyle and try to possible ways boost immunity. The state must arrange quarantines in a timely manner and provide good medical care.
Plant viruses
Artificial viruses
The ability to create viruses in artificial conditions could have many consequences. The virus cannot completely die out as long as there are bodies sensitive to it.
Viruses are weapons
Viruses and the biosphere
On this moment extracellular agents can "show off" the largest number individuals and species living on planet Earth. They perform an important function by regulating the populations of living organisms. Very often they form a symbiosis with animals. For example, the venom of some wasps contains components of viral origin. However, their leading role in the existence of the biosphere is life in the sea and ocean.
One teaspoon of sea salt contains approximately a million viruses. Their main goal is to regulate life in aquatic ecosystems. Most of them are absolutely harmless to flora and fauna
But these are not all positive qualities. Viruses regulate the process of photosynthesis, therefore increasing the percentage of oxygen in the atmosphere.
Sizes – from 15 to 2000 nm (some plant viruses). The largest among animal and human viruses is the causative agent of smallpox - up to 450 nm.
Simple viruses have an envelope - capsid, which consists only of protein subunits ( capsomeres). The capsomeres of most viruses have helical or cubic symmetry. Virions with helical symmetry are rod-shaped. Most viruses that infect plants are built according to the spiral type of symmetry. Most viruses that infect human and animal cells have a cubic type of symmetry.
Complex viruses
Complex viruses can be additionally covered with a lipoprotein surface membrane with glycoproteins that are part of the plasma membrane of the host cell (for example, smallpox viruses, hepatitis B), that is, they have supercapsid. With the help of glycoproteins, specific receptors are recognized on the surface of the host cell membrane and the viral particle attaches to it. The carbohydrate regions of glycoproteins protrude above the surface of the virus in the form of pointed rods. The additional envelope can merge with the plasma membrane of the host cell and facilitate the penetration of the contents of the viral particle deep into the cell. Additional shells may include enzymes that ensure the synthesis of viral nucleic acids in the host cell and some other reactions.
Bacteriophages have a rather complex structure. They are classified as complex viruses. For example, bacteriophage T4 consists of an expanded part - a head, a process and tail filaments. The head consists of a capsid that contains nucleic acid. The process includes a collar, a hollow shaft surrounded by a contractile sheath resembling an extended spring, and a basal plate with caudal spines and filaments.
Classification of viruses
The classification of viruses is based on the symmetry of the viruses and the presence or absence of an outer shell.
| Deoxyviruses | Riboviruses | ||
| DNA double-stranded | DNA single-stranded | RNA double-stranded | RNA single-stranded |
| Cubic symmetry type: – without outer shells (adenoviruses); - With outer shells(herpes) | Cubic symmetry type: – without outer membranes (some phages) | Cubic symmetry type: – without outer shells (retroviruses, plant wound tumor viruses) | Cubic symmetry type: – without outer shells (enteroviruses, poliovirus) Spiral symmetry type: – without outer shells (tobacco mosaic virus); – with outer membranes (influenza, rabies, oncogenic RNA-containing viruses) |
| Mixed type of symmetry (T-paired bacteriophages) | |||
| Without a certain type of symmetry (pox) | |||
Viruses exhibit vital activity only in the cells of living organisms. Their nucleic acid is capable of causing the synthesis of viral particles in the host cell. Outside the cell, viruses do not show signs of life and are called virions.
The life cycle of the virus consists of two phases: extracellular(virion), in which it does not show signs of vital activity, and intracellular. Viral particles outside the host’s body do not lose their ability to infect for some time. For example, the polio virus can remain infectious for several days, and smallpox for months. The hepatitis B virus retains it even after short-term boiling.
The active processes of some viruses occur in the nucleus, others in the cytoplasm, and in some, both in the nucleus and in the cytoplasm.
Types of interaction between cells and viruses
There are several types of interactions between cells and viruses:
- Productive – the nucleic acid of the virus induces the synthesis of its own substances in the host cell with the formation of a new generation.
- Abortive – reproduction is interrupted at some stage, and a new generation is not formed.
- Virogenic – the nucleic acid of the virus is integrated into the genome of the host cell and is not capable of reproduction.
Structure
Examples of icosahedral virion structures.
A. A virus that does not have a lipid envelope (for example, picornavirus).
B. Enveloped virus (eg, herpesvirus).
The numbers indicate: (1) capsid, (2) genomic nucleic acid, (3) capsomere, (4) nucleocapsid, (5) virion, (6) lipid envelope, (7) membrane envelope proteins.
Classification
Squad ( -virales) Family ( -viridae) Subfamily ( -virinae) Genus ( -virus) View ( -virus)Baltimore classification
Nobel laureate, biologist David Baltimore, proposed his own classification scheme for viruses based on differences in the mechanism of mRNA production. This system includes seven main groups:
- (I) Viruses that contain double-stranded DNA and do not have an RNA stage (for example, herpesviruses, poxviruses, papovaviruses, mimivirus).
- (II) Double-stranded RNA viruses (eg rotaviruses).
- (III) Viruses containing a single-stranded DNA molecule (eg, parvoviruses).
- (IV) Viruses containing a single-stranded RNA molecule of positive polarity (for example, picornaviruses, flaviviruses).
- (V) Viruses containing a single-stranded RNA molecule of negative or double polarity (for example, orthomyxoviruses, filoviruses).
- (VI) Viruses containing a single-stranded RNA molecule and having life cycle the stage of DNA synthesis on an RNA template, retroviruses (for example, HIV).
- (VII) Viruses containing double-stranded DNA and having in their life cycle the stage of DNA synthesis on an RNA template, retroid viruses (for example, hepatitis B virus).
Currently, both systems are used simultaneously to classify viruses, as complementary to each other.
Further division is made on the basis of such characteristics as genome structure (presence of segments, circular or linear molecule), genetic similarity with other viruses, the presence of a lipid membrane, taxonomic affiliation of the host organism, and so on.
Story
Application of viruses
Links
- “The Nobel Committee was hit by viruses” Article. Newspaper "Kommersant" No. 181 (3998) dated 10/07/2008.
Literature
- Mayo M.A., Pringle C.R. Virus taxonomy - 1997 // Journal of General Virology. - 1998. - No. 79. - P. 649-657.
Sizes – from 15 to 2000 nm (some plant viruses). The largest among animal and human viruses is the causative agent of smallpox - up to 450 nm.
Simple viruses have an envelope - capsid, which consists only of protein subunits ( capsomeres). The capsomeres of most viruses have helical or cubic symmetry. Virions with helical symmetry are rod-shaped. Most viruses that infect plants are built according to the spiral type of symmetry. Most viruses that infect human and animal cells have a cubic type of symmetry.
Complex viruses
Complex viruses can be additionally covered with a lipoprotein surface membrane with glycoproteins that are part of the plasma membrane of the host cell (for example, smallpox viruses, hepatitis B), that is, they have supercapsid. With the help of glycoproteins, specific receptors are recognized on the surface of the host cell membrane and the viral particle attaches to it. The carbohydrate regions of glycoproteins protrude above the surface of the virus in the form of pointed rods. The additional envelope can merge with the plasma membrane of the host cell and facilitate the penetration of the contents of the viral particle deep into the cell. Additional shells may include enzymes that ensure the synthesis of viral nucleic acids in the host cell and some other reactions.
Bacteriophages have a rather complex structure. They are classified as complex viruses. For example, bacteriophage T4 consists of an expanded part - a head, a process and tail filaments. The head consists of a capsid that contains nucleic acid. The process includes a collar, a hollow shaft surrounded by a contractile sheath resembling an extended spring, and a basal plate with caudal spines and filaments.
Classification of viruses
The classification of viruses is based on the symmetry of the viruses and the presence or absence of an outer shell.
| Deoxyviruses | Riboviruses | ||
| DNA double-stranded | DNA single-stranded | RNA double-stranded | RNA single-stranded |
| Cubic symmetry type: – without outer shells (adenoviruses); – with external membranes (herpes) | Cubic symmetry type: – without outer membranes (some phages) | Cubic symmetry type: – without outer shells (retroviruses, plant wound tumor viruses) | Cubic symmetry type: – without outer shells (enteroviruses, poliovirus) Spiral symmetry type: – without outer shells (tobacco mosaic virus); – with outer membranes (influenza, rabies, oncogenic RNA-containing viruses) |
| Mixed type of symmetry (T-paired bacteriophages) | |||
| Without a certain type of symmetry (pox) | |||
Viruses exhibit vital activity only in the cells of living organisms. Their nucleic acid is capable of causing the synthesis of viral particles in the host cell. Outside the cell, viruses do not show signs of life and are called virions.
The life cycle of the virus consists of two phases: extracellular(virion), in which it does not show signs of vital activity, and intracellular. Viral particles outside the host’s body do not lose their ability to infect for some time. For example, the polio virus can remain infectious for several days, and smallpox for months. The hepatitis B virus retains it even after short-term boiling.
The active processes of some viruses occur in the nucleus, others in the cytoplasm, and in some, both in the nucleus and in the cytoplasm.
Types of interaction between cells and viruses
There are several types of interactions between cells and viruses:
- Productive – the nucleic acid of the virus induces the synthesis of its own substances in the host cell with the formation of a new generation.
- Abortive – reproduction is interrupted at some stage, and a new generation is not formed.
- Virogenic – the nucleic acid of the virus is integrated into the genome of the host cell and is not capable of reproduction.
1.INTRODUCTION PAGE 1
2. EVOLUTIONARY ORIGIN PAGE 2
3. PROPERTIES OF VIRUSES. NATURE OF VIRUSES. PAGE 2
4.STRUCTURE AND CLASSIFICATION OF VIRUSES PAGE 3
5.INTERACTION OF VIRUS WITH CELL P.6
6. THE IMPORTANCE OF VIRUSES PAGE 7
7. VIRAL DISEASES PAGE 9
8. FEATURES OF VIRUS EVOLUTION AT THE MODERN
STAGE. PAGE 14
9.CONCLUSION. PAGE 15
10. LIST OF REFERENCES USED. PAGE 16
Introduction
By the end of the last century, no one doubted that every infectious disease is caused by its own microbe, which can be successfully combated.
“Just give it time,” said bacteriological scientists, “and soon there won’t be a single disease left.” But years passed, and the promises were not fulfilled. People became infected with measles, foot-and-mouth disease, polio, trachoma, smallpox, yellow fever, and influenza. Millions of people died from terrible diseases, but the microbes that caused them could not be found.
Finally in 1892 Russian scientist D.I. Ivanovsky was on the right track. Studying tobacco mosaic, a disease of tobacco leaves, he came to the conclusion that it is not caused by a microbe, but by something smaller. This “something” penetrates through the finest filters capable of retaining bacteria, does not multiply in artificial media, dies when heated, and cannot be seen in a light microscope. Filterable poison!
This was the scientist's conclusion. But poison is a substance, and the causative agent of tobacco disease was a being. It reproduced well in plant leaves. Danish botanist Martin Willem Beirinick called this new “something” a virus, adding that a virus is a “liquid, living, infectious, principle.” Translated from Latin, “virus” means “poison”
A few years later, F. Leffler and P. Frosch discovered that the causative agent of foot-and-mouth disease, a disease often found in livestock, also passes through bacterial filters. Finally, in 1917, Canadian bacteriologist F. de Herelle discovered a bacteriophage, a virus that infects bacteria.
Thus, viruses of plants, animals and microorganisms were discovered. These events marked the beginning of a new science - virology, studying non-cellular life forms.
Evolutionary origin of viruses
Natural viruses still cause heated discussions among specialists. The reason for this is largely due to the numerous and often very contradictory hypotheses that have been expressed to date and, unfortunately, have not been objectively proven.
It seems more plausible hypothesis about the endogenous origin of viruses. According to it, viruses are a fragment of once cellular nucleic acid that has adapted to separate replication. This version is to some extent confirmed by the existence of plasmids in bacterial cells, the behavior of which is in many ways similar to viruses. Along with this, there is also a “cosmic” hypothesis, according to which viruses did not evolve on Earth at all, but were brought to us from the Universe through some cosmic bodies.
Properties of viruses. Nature of viruses
2. They do not have their own metabolism and have a very limited number of enzymes. For reproduction, the metabolism of the host cell, its enzymes and energy are used.
Viruses do not reproduce on artificial nutrient media- They are too picky about food. Ordinary meat broth, which suits most bacteria, is not suitable for viruses . They need living cells, and not just any, strictly defined ones. Like other organisms, viruses are capable of reproduction. Viruses have heredity.. The hereditary characteristics of viruses can be taken into account by the range of hosts affected and the symptoms of the diseases caused, as well as by the specificity of the immune reactions of natural hosts or artificially immunized experimental animals. The sum of these characteristics makes it possible to clearly determine the hereditary properties of any virus, and even more - its varieties that have clear genetic markers, for example: the neurotropism of some influenza viruses, etc. . Variation is the other side of heredity, and in this respect, viruses are similar to all other organisms that inhabit our planet. At the same time, in viruses one can observe both genetic variability associated with changes in the hereditary substance, and phenotypic variability associated with the manifestation of the same genotype in different conditions.
Structure and classification of viruses
Viruses cannot be seen with an optical microscope because their sizes are smaller than the wavelength of light. They can only be seen using an electron microscope.
Viruses consist of the following main components :
1 . The core is the genetic material (DNA or RNA) that carries information about several types of proteins necessary for the formation of a new virus.
2 . The protein shell, which is called the capsid (from Latin word capsule - box). It is often constructed from identical repeating subunits - capsomeres. Capsomeres form structures with a high degree of symmetry.
3 . Additional lipoprotein membrane. It is formed from the plasma membrane of the host cell and is found only in relatively large viruses(flu, herpes).
Capsids and the additional shell have protective functions, as if protecting the nucleic acid. In addition, they facilitate the penetration of the virus into the cell. A fully formed virus is called a virion.
The schematic structure of an RNA-containing virus with a helical type of symmetry and an additional lipoprotein envelope is shown on the left in Figure 2; an enlarged cross section is shown on the right.
Fig.2. Schematic structure of the virus: 1 - core (single-stranded RNA); 2 - protein shell (Capsid); 3 - additional lipoprotein membrane; 4 - Capsomeres (structural parts of the Capsid).
The number of capsomeres and the way they are folded are strictly constant for each type of virus. For example, the polio virus contains 32 capsomeres, and the adenovirus contains 252.
Since the basis of all living things is genetic structures, viruses are now classified according to the characteristics of their hereditary substance - nucleic acids. All viruses are divided into two large groups :DNA viruses(deoxyviruses) and RNA viruses(riboviruses). Each of these groups is then divided into viruses with double-stranded and single-stranded nucleic acids. The next criterion is the type of symmetry of the virions (depending on the way the capsomeres are laid), the presence or absence of outer shells, according to the host cells. In addition to these classifications, there are many others. For example, by the type of transmission of infection from one organism to another.
Fig.3. Schematic representation of the arrangement of capsomeres in the capsid of viruses. The influenza virus has a helical type of symmetry - A. Cubic type of symmetry in viruses: herpes - b, adenovirus - V, polio - G
ENVELOPEDouble-stranded The genetic material of the virus (DNA or RNA) is surrounded by a protein shell. DNA structure of viruses
/>smallpox viruses
/>herpes - viruses
Single-stranded RNA
/>measles, mumps viruses
/>Rabies viruses
/>leukemia and AIDS viruses
SHELLLESS
Double-stranded DNA
/>irido - viruses
/>adeno - viruses
Virus-cell interaction
Viruses can live and reproduce only in the cells of other organisms. Outside the cells of organisms, they do not show any signs of life. In this regard, viruses are either an extracellular resting form (varion),
or intracellular replicating - vegetative. Varions demonstrate excellent viability. In particular, they can withstand pressures of up to 6000 atm and tolerate high doses of radiation, but they die at high temperatures, irradiation with UV rays, and exposure to acids and disinfectants.
Virus-cell interaction passes through several stages in sequence:
1. First stage represents adsorption of ions on the surface of the target cell, which for this purpose must have the appropriate surface receptors. It is with them that the viral particle specifically interacts, after which they are firmly bound; for this reason, cells are not susceptible to all viruses. This is precisely what explains the strict definiteness of the routes of penetration of viruses. For example, the cells of the mucous membrane of the respiratory tract have receptors for the influenza virus, but the cells of the skin do not. Therefore, you cannot get the flu through the skin - viral particles must be inhaled with air, the hepatitis A or B virus penetrates and multiplies only in liver cells, and the mumps virus (mumps) - in the cells of the parotid salivary glands, etc.
2. Second stage consists of penetration the whole varion or its nucleic acid into the host cell.
3.Third stage called deproteinization During this process, the carrier of the genetic information of the virus, its nucleic acid, is released.
4. During fourth stage based on viral nucleic acid synthesis of compounds necessary for the virus.
5.B fifth stage is happening synthesis of viral particle components- nucleic acid and capsid proteins, and all components are synthesized multiple times.
6. During sixth stage from previously synthesized multiple copies of nucleic acid and proteins new virions are formed by self-assembly
7.Last- seventh stage- represents the exit of newly assembled viral particles from the host cell. U different viruses This process is not the same. For some viruses, this is accompanied by cell death due to the release of lysosome lytic enzymes - cell lysis. In others, varions leave a living cell by budding, but even in this case the cell dies over time.
The time that elapses from the moment the virus enters the cell until the release of new variants is called latent or latent period. It can vary widely: from several hours (5-6 for smallpox and influenza viruses) to several days (measles viruses, adenoviruses, etc.
Another route of entry into cells for bacterial viruses is bacteriophages .Thick cell walls do not allow the receptor protein, together with the virus attached to it, to plunge into the cytoplasm, as happens when animal cells are infected. Therefore, the bacteriophage introduces a hollow rod into the cell and pushes through it the DNA (or RNA) found in it head The genome of the bacteriophage enters the cytoplasm, and the capsid remains outside. Into the cytoplasm bacterial cells begin reduplication of the bacteriophage genome, synthesis of its proteins and formation of the capsid. After a certain period of time, the bacterial cell dies, and mature phage particles are released into the environment.
Bacteriophages that form a new generation of phage particles in infected cells, which leads to the lysis (destruction) of the bacterial cell, are called virulent phages.
Some bacteriophages do not replicate inside the host cell. Instead, their nucleic acid is incorporated into the host DNA, forming with it a single molecule capable of replication. These phages are named temperate phages,or prophages. The prophage does not have a lytic effect on the host cell and, when dividing, replicates along with the cellular DNA. Bacteria containing a prophage are called lysogenic. They show resistance to the phage they contain, as well as to other phages close to it. The connection between the prophage and the bacterium is very strong, but it can be disrupted by inducing factors (UV rays, ionizing radiation, chemical mutagens). It should be noted that lysigenic bacteria can change properties (for example, release new toxins).
The meaning of viruses
Viruses of bacteria, plants, insects, animals and humans are scientifically known. There are more than 1000 of them. Processes associated with the reproduction of the virus most often, but not always, damage and destroy the host cell. The reproduction of viruses, coupled with the destruction of cells, leads to the occurrence of painful conditions in the body. Viruses cause many human diseases: measles, mumps, influenza, polio, rabies, smallpox, yellow fever, trachoma, encephalitis, some oncological (tumor) diseases, AIDS. It is not uncommon for people to start growing warts. Everyone knows how after a cold they often “sweep” the lips and wings of the nose. These are also all viral diseases. Scientists have found that many viruses live in the human body, but they do not always manifest themselves. Only a weakened body is susceptible to the effects of a pathogenic virus. There are a variety of ways to become infected with viruses: through the skin through insect and tick bites; through saliva, mucus and other secretions of the patient; through the air; with food; sexually and others. Droplet infection is the most the usual way spread of respiratory diseases. Coughing and sneezing release millions of tiny droplets of liquid (mucus and saliva) into the air. These droplets, along with the living microorganisms they contain, can be inhaled by other people, especially in crowded places. In animals, viruses cause foot and mouth disease, plague, and rabies; uninsects - polyhedrosis, granulomatosis; in plants - mosaic or other changes in the color of leaves or flowers, leaf curl and other changes in shape, dwarfism; finally, in bacteria - their decay. The idea of viruses as “destroyers” who stop at nothing was preserved during the study of a special group of viruses that infect bacteria. It's about obbacteriophages. The ability of phages to destroy bacteria can be used to treat some diseases caused by these bacteria. Phages truly became the first group of viruses “tamed” by humans. They quickly and mercilessly dealt with their closest neighbors in the microworld. Plague, typhoid, dysentery, and cholera vibrios literally “melted” before our eyes after meeting these viruses. They began to be used to prevent and treat many infectious diseases, but, unfortunately, the first successes were followed by failures. This was due to the fact that in the human body, phages did not attack bacteria as actively as in a test tube. In addition, the bacteria turned out to be “cunning” than their enemies: they very quickly adapted to the phages and became insensitive to their action.
After the discovery of antibiotics, phages receded into the background as medicine, but they are still successfully used to recognize bacteria. The fact is that phages are able to very accurately find “their bacteria” and quickly dissolve them. Similar properties of phages form the basis of therapeutic diagnostics. This is usually done like this: bacteria isolated from the patient’s body are grown on a solid nutrient medium, after which various phages, for example, dysentery, typhoid, cholera and others, are applied to the resulting “lawn”. After 24 hours, the dishes are examined under the light and it is determined which phage caused the dissolution of the bacteria. If a dysentery phage had such an effect, then dysentery bacteria were isolated from the patient’s body, if typhoid, then typhoid bacteria were isolated.
Sometimes viruses that infect animals and insects come to the aid of humans. More than twenty years ago in Australia, the problem of fighting wild rabbits became acute. The number of these rodents reached alarming proportions. They destroyed crops faster than locusts and became a real national disaster. Conventional methods of dealing with them turned out to be ineffective. And then the scientists released them to fight rabbits special virus, capable of destroying almost all infected animals. But how to spread this disease among timid and cautious rabbits? The mosquitoes helped. They played the role of "flying needles", spreading the virus from rabbit to rabbit. At the same time, the mosquitoes remained completely healthy.
There are other examples of the successful use of viruses to destroy pests. Everyone knows the damage caused by caterpillars and sawflies. The former eat the leaves of useful plants, the latter infect trees in gardens and forests. They are fought by the so-called polyhedrosis and granulosis viruses, which are sprayed in small areas with atomizers, and airplanes are used to treat large areas. This was done in the USA (in California) when fighting caterpillars that infect alfalfa fields, and in Canada when destroying the pine sawfly. It is also promising to use viruses to combat caterpillars that infect cabbage and beets, as well as to destroy house moths.
What will happen to a cell if it is infected with not one, but two viruses? If you decided that in this case the cell’s disease would worsen and its death would accelerate, then you were mistaken. It turns out that the presence of one virus in a cell often reliably protects it from the destructive effects of another. This phenomenon was called virus interference by scientists. It is associated with the production of a special protein - interferon, which in cells activates a protective mechanism that can distinguish viral from non-viral and selectively suppress viral. Interferon suppresses the reproduction of most viruses (if not all) in cells. Interferon, produced as a therapeutic drug, is now used for the treatment and prevention of many viral diseases.
What other useful things can we expect from viruses in the future? Let's move into the realm of speculation. First of all, it is worth recalling genetic engineering. Viruses can provide scientists with invaluable benefits by capturing the necessary genes in some cells and transferring them to others. Finally, there is another possibility of using viruses. Scientists have discovered a virion that is capable of selectively destroying some mouse tumors. Viruses that kill human tumor cells have also been obtained. If it is possible to deprive these viruses of their pathogenic properties and at the same time retain their ability to selectively destroy malignant tumors, then in the future it may be possible to obtain powerful tool to combat these serious diseases. The search for such viruses is underway, and now this work no longer seems fantastic and hopeless.
Let's briefly look at some viral diseases:
Smallpox
Smallpox - one of the oldest diseases. In the past, it was the most common and most dangerous disease. A description of smallpox was found in the Egyptian papyrus of Amenophis I, compiled 4000 BC. Smallpox lesions were preserved on a cozhemumia buried in Egypt 3000 BC. In the 16th – 18th centuries in Western Europe, in some years, up to 12 million people fell ill with smallpox, of whom up to 1.5 million died. Its devastating power was not inferior to the power of the plague. The problem of preventing smallpox was solved only at the end of the 18th century by the English rural doctor Edward Jenner. Jenner was the first to prove that through vaccination it is possible to suppress the spread of infectious diseases and banish them from the face of the Earth. The first mention of smallpox in Russia dates back to the 15th century. In 1610, the infection was brought to Siberia, where a third of the local population died out. People fled to the forests of the tundra and mountains, displayed idols, burned scars like pockmarks on their faces in order to deceive this evil spirit - everything was in vain, nothing could stop the ruthless killer. Smallpox is an acute infectious disease characterized by general intoxication, fever and rash on the skin and mucous membranes. Smallpox is a quarantine infection. The source of infection is a sick person, from the first days of illness until the scabs completely fall off. Transmission of the pathogen occurs mainly by air - by drip, however, infection is also possible through airborne dust. Smallpox was widespread in Asia, Africa, and South America. In the USSR, smallpox was eradicated in 1937. Currently, it has been eliminated all over the world.
FLU
Influenza, in our opinion, is not such a serious disease, but it remains the “king” of epidemics. None of the diseases known today can cover hundreds of millions of people in a short time, and more than 2.5 billion people fell ill with the flu in just one pandemic (widespread epidemic).
Since the end of the nineteenth century. Humanity has experienced four severe influenza pandemics: in 1889-1890, 1918-1920, 1957-1959 and 1968-1969. Pandemic 1918-1920 ("Spanish flu") carried away 20 million lives . Never since has the flu caused such a high mortality rate. 1957-1959 (“Asian flu”) killed about 1 million people.
Several varieties of influenza virus are known - A, B, C, etc.; The internal part of the influenza virus - the nucleotide (or core) contains single-stranded RNA enclosed in a protein sheath. This is the most stable part of the virion, since it is the same in all influenza viruses of the same type. Influenza type A is the culprit of pandemics. Influenza B is less common and causes more limited epidemics; influenza C is even rarer.
Due to the fact that immunity to influenza is short-term and specific, repeated illness is possible in one season. According to statistics, an average of 20-35% of the population suffers from influenza every year.
The source of infection is a sick person; Patients with a mild form of the virus are the most dangerous as spreaders of the virus, since they do not isolate themselves in a timely manner - they go to work, use public transport, and visit places of entertainment. The infection is transmitted from a sick person to a healthy person through airborne droplets when talking, sneezing, coughing or through household items.
Bird flu in humans:
Influenza A viruses can infect not only humans, but also some species of poultry, including chickens, ducks, pigs, horses, ferrets, seals and whales. Influenza viruses that infect birds are called “avian (chicken) flu” viruses. All species of birds can get avian influenza, although some species are less susceptible than others. Bird flu does not cause epidemics among wild birds and is asymptomatic, but among domestic birds it can cause severe illness and death.
Avian influenza virus, as a rule, does not infect people, but there have been cases of illness and even death among people during outbreaks in 1997-/>1999 and 2003-2004. In this case, a person is most likely the final link in the transmission of the influenza virus (you can get sick by contact with live infected poultry or by eating raw infected meat), because There are still no recorded cases of reliable transmission of this virus from person to person.
So in 1997, the avian influenza virus (H5N1) was isolated in Hong Kong, which infected both chickens and people. This was the first time it was discovered that the avian influenza virus could be transmitted directly from birds to humans. During this outbreak, 18 people were hospitalized and 6 of them died. Scientists have determined that the virus spread directly from birds to humans.
Since the end of 2003, during the avian influenza epidemic that swept through Southeast and East Asia, 66 people have died from this disease, mostly in close contact with infected animals.
Also in 2003, avian influenza viruses (H7N7) and (H5N1) were detected in the Netherlands in 86 people caring for infected birds. The disease was asymptomatic or mild. Most often, the manifestations of the disease were limited to eye infection with some signs of respiratory diseases.
Recently, bird flu was discovered in Russia and Kazakhstan. However, not a single case of defeat dangerous virus people in these countries have not yet been recorded
Symptoms of bird flu in humans:
Symptoms of avian influenza in humans vary from typical flu-like symptoms (very heat, difficulty breathing, cough, sore throat and muscle pain) to eye infection (conjunctivitis). This virus is dangerous because it can very quickly lead to pneumonia, and, in addition, can cause serious complications on the heart and kidneys.
2004 - Most widespread outbreak of avian influenza (H5N1) in humans. The main distinctive features of the 2004 influenza virus can be briefly formulated as follows:
The virus has become more infectious, indicating that the virus has mutated.
The virus has crossed the interspecies barrier from birds to humans, but so far there is no evidence that the virus is transmitted directly from person to person (all sick people had direct contact with an infected bird).
The virus infects and kills mainly children. The source of infection and the route of spread of the virus have not been determined, which makes the situation with the spread of the virus practically uncontrollable. Measures to prevent spread - complete destruction total poultry population. Treatment of bird flu in humans:
Research to date suggests that drugs developed for human influenza strains will be effective against avian influenza infections in humans, but it is possible that influenza strains may become resistant to such drugs, rendering the drugs ineffective. It was found that the isolated virus is sensitive to amantadine and rimantadine, which inhibit the reproduction of the influenza A virus and are used in the treatment of human influenza.
What is the reason for the close attention to bird flu these days:
All influenza viruses have the ability to change. There is a possibility that in the future the avian influenza virus could change in such a way that it could infect people and spread easily from person to person. Because these viruses do not typically infect humans, there is very little or no immune defense against such viruses in the human population.
If the avian influenza virus becomes capable of infecting people, an influenza pandemic could begin. Experts from the World Health Organization (WHO) believe that the bird flu pandemic could lead to the death of 150 million people on Earth.
This fact is confirmed by American and British scientists: the results of their research indicate that the Spanish flu (1918) was so deadly due to the fact that it evolved from bird flu and contained a unique protein to which humans had no immunity.
Currently, there is a hypothesis that the pandemic influenza virus originated through the transfer of genes from the reservoir of waterfowl to humans through pigs.
In addition, the bird flu virus, unlike the human one, is very stable in the external environment - even in the carcasses of dead birds it can live for up to one year, which increases the risk.
AIDS- Acquired immune deficiency syndrome is a new infectious disease that experts recognize as the first truly global epidemic in the known history of mankind. Neither the plague, smallpox, nor cholera are precedents, since AIDS is decidedly unlike any of these or other known human diseases. The plague claimed tens of thousands of lives in the regions where the epidemic broke out, but never engulfed the entire planet at once. In addition, some people, having been ill, survived, acquired immunity and took on the labor of caring for the sick and restoring the damaged economy. AIDS is not a rare disease that affects a few people by chance. Leading experts currently define AIDS as a “global health crisis”, as the first truly all-earthly and unprecedented epidemic of an infectious disease, which still, after the first decade of the epidemic, is not controlled by medicine and every infected person dies from it.
By 1991, AIDS was registered in all countries of the world except Albania. In the most developed country in the world - the United States - already at that time one out of every 100-200 people was infected, every 13 seconds another US resident was infected, and by the end of 1991, AIDS in this country had become third in mortality, overtaking cancer. Currently, the countries in sub-Saharan Africa are leading in terms of the number of people infected with the virus. An entire country in Africa - Zimbabwe - may become extinct as a result of AIDS: every day up to 300 people die here from this disease! Among the adult population of large cities in Botswana, the incidence reaches 30%. Every tenth infant is already infected with the HIV virus. So far, AIDS forces one to recognize itself as a fatal disease in 100% of cases.
The first people with AIDS were identified in 1981, and in 1983. managed to prove that it is caused by a previously unknown human virus from the retrovirus family. This virus contains only its own enzyme - reverse transcriptase (RNA-dependent DNA pomerase), which is part of only these viruses. Its discovery was a real revolution in biology, as it showed the possibility transmission of genetic information not only according to the classical DNA - RNA - protein scheme, but also by reverse transcription from RNA to DNA. This is how a “false program” (provirus) appears in the cell, which changes the genome much more than is possible with “normal” evolutionary variability.
In the human body retrovirusHIV infects only certain cells - the so-called T4 lymphocytes by binding to a special membrane protein. Unfortunately, these are the cells that play the main role role V immune system management. When introducing itself, the virus introduces its RNA, on the matrix of which proviral DNA is synthesized, in order to then integrate into the genome of the host cell. In this capacity, HIV can be present in the body for up to ten years without manifesting itself in any way.
But if, under the influence of some other infections, lymphocytes are activated, the built-in area “wakes up” and begins to actively synthesize HIV particles. Then the viruses destroy the membrane and kill lymphocytes, which leads to the destruction of the immune system, as a result of which the body loses its protective properties and is unable to resist pathogens of various infections and kill tumor cells. The insidiousness of HIV in its unusual high ability to mutations- which makes it impossible to create an effective vaccine and a universal cure.
How does infection occur? ? The source of infection is a person infected with the immunodeficiency virus. This may be a patient with various manifestations of the disease, or a person who is a carrier of the virus, but has no signs of the disease (asymptomatic virus carrier).
Routes of transmission of infection: sexual,
AIDS is transmitted only from person to person:
1. sexually (horizontal route)
2. parenteral, when a viral agent is introduced directly into the blood of a susceptible organism (blood transfusion or its preparations), organ transplantation or intravenous administration of drugs (drugs) with shared syringes or needles, performance of ritual ceremonies associated with bloodletting, cuts with an HIV-infected instrument.
3. from mother to fetus and newborn (vertical path).
Risk groups for contracting AIDS include homosexual men, intravenous drug users, prostitutes, people with a large number of sexual partners, frequent donors, hemophiliacs, children born from HIV-infected individuals.
Prevention measures . The main condition is your behavior!
Features of the evolution of viruses at the present stage.
The evolution of viruses in the era of scientific and technological progress, as a result of powerful pressure from factors, proceeds much faster than before. As examples of such intensively developing processes in the modern world, we can point to the pollution of the external environment with industrial waste, the widespread use of pesticides, antibiotics, vaccines and other biological products, the huge concentration of population in cities, the development of modern vehicles, the economic development of previously unused territories, the creation of industrial livestock farming with the largest numbers of and population density of livestock farms. All this leads to the emergence of previously unknown pathogens, changes in the properties and circulation pathways of previously known viruses, as well as significant changes in the susceptibility and resistance of human populations.
The influence of environmental pollution.
The current stage of development of society is associated with intense pollution of the external environment. At certain levels of air pollution with certain chemicals and dust from industrial waste, a noticeable change in the resistance of the body as a whole occurs, especially in the cells and tissues of the respiratory tract. There is evidence that under these conditions, some respiratory viral infections, such as influenza, are noticeably more severe.
Consequences of mass use of pesticides.
This may lead to the emergence of clones and populations of viruses with new properties and, as a result, new unexplored epidemics.
Conclusion
Fight with viral infections is associated with numerous difficulties, among which especially noteworthy is the immunity of viruses to antibiotics. Viruses are actively mutating, and new strains regularly appear against which “weapons” have not yet been found. First of all, this applies to RNA viruses, whose genome is usually larger and, therefore, less stable. To date, the fight against many viral infections is in favor of humans, mainly due to universal vaccination of the population for preventive purposes. Such events ultimately led to the fact that, according to experts, the smallpox virus has now disappeared from nature. As a result of universal vaccination in our country, in 1961. Epidemic poliomyelitis was eradicated. However, nature still tests humans, from time to time, presenting surprises in the form of new viruses that cause terrible diseases. The most striking example is the human immunodeficiency virus, which humans are still losing the fight against. Its spread is already consistent with a pandemic.
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