Viruses were discovered by D.I. Ivanovsky (1892, tobacco mosaic virus).

If viruses are isolated in their pure form, then they exist in the form of crystals (they do not have their own metabolism, reproduction and other properties of living things). Because of this, many scientists consider viruses to be an intermediate stage between living and nonliving objects.

Viruses are a non-cellular life form. Viral particles (virions) are not cells:

• viruses are much smaller than cells;
• viruses are much simpler than cells in structure - they consist only of nucleic acid and a protein shell, consisting of many identical protein molecules.
• viruses contain either DNA or RNA.

Synthesis of virus components:

• The nucleic acid of a virus contains information about viral proteins. The cell makes these proteins on its own, on its ribosomes.
• The cell reproduces the nucleic acid of the virus itself, with the help of its enzymes.
• Then the self-assembly of viral particles occurs.

The value of viruses:

• cause infectious diseases (flu, herpes, AIDS, etc.)
• some viruses can insert their DNA into the chromosomes of the host cell, causing mutations.

AIDS

The AIDS virus is very unstable, easily destroyed in the air. It can only be infected through sexual intercourse without a condom and through contaminated blood transfusion.

Answer

Establish a correspondence between the signs of a biological object and the object to which this sign belongs: 1) bacteriophage, 2) Escherichia coli. Write down the numbers 1 and 2 in the correct order.
A) consists of nucleic acid and capsid
B) murein cell wall
C) outside the body is in the form of crystals
D) can be in symbiosis with a person
E) has ribosomes
E) has a tail channel

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Choose the one that is most correct. Precellular life forms are being studied by science
1) virology
2) mycology
3) bacteriology
4) histology

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Choose the one that is most correct. The AIDS virus infects human blood
1) erythrocytes
2) platelets
3) lymphocytes
4) platelets

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2. Choose three correct answers out of six and write down the numbers under which they are indicated. Viruses as opposed to bacteria
1) have an unformed core
2) reproduce only in other cells
3) do not have membrane organelles
4) carry out chemosynthesis
5) are able to crystallize
6) formed by a protein coat and nucleic acid

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3. Choose three correct answers out of six and write down the numbers under which they are indicated. Viruses as opposed to bacteria
1) have a cellular structure
2) have an unformed core
3) formed by a protein coat and nucleic acid
4) belong to free-living forms
5) reproduce only in other cells
6) are a non-cellular life form

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Choose the one that is most correct. The cells of which organisms are affected by the bacteriophage?
1) lichens
2) mushrooms
3) prokaryotes
4) the simplest

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Choose the one that is most correct. The immunodeficiency virus primarily affects
1) erythrocytes
2) platelets
3) phagocytes
4) lymphocytes

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Choose the one that is most correct. In what environment does the AIDS virus usually die?
1) in the lymph
2) in breast milk
3) in saliva
4) in the air

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Choose the one that is most correct. Viruses have such signs of living as
1) food
2) growth
3) metabolism
4) heredity

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1. Establish the correct sequence of stages of reproduction of DNA-containing viruses. Write down the corresponding sequence of numbers in the table.
1) release of the virus into the environment
2) viral protein synthesis in the cell
3) the introduction of DNA into the cell
4) synthesis of virus DNA in the cell
5) attachment of the virus to the cell

Answer

2. Establish the sequence of stages in the life cycle of a bacteriophage. Write down the corresponding sequence of numbers.
1) biosynthesis of DNA and proteins of a bacteriophage by a bacterial cell
2) rupture of the bacterial membrane, release of bacteriophages and infection of new bacterial cells
3) penetration of bacteriophage DNA into the cell and its incorporation into the circular DNA of the bacterium
4) attachment of the bacteriophage to the membrane of the bacterial cell
5) assembly of new bacteriophages

Answer

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1. Establish a correspondence between a trait of an organism and a group for which it is characteristic: 1) prokaryotes, 2) viruses.
A) the cellular structure of the body
B) the presence of its own metabolism
C) embedding of its own DNA into the DNA of the host cell
D) consists of a nucleic acid and a protein envelope
D) reproduction by dividing in two
E) the ability to reverse transcription

Answer

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Answer

Choose two correct answers out of five and write down the numbers under which they are indicated. Metabolism as a property of living things is characteristic of
1) plant viruses
2) the simplest
3) soil bacteria
4) animal viruses
5) bacteriophages

Answer

© D.V. Pozdnyakov, 2009-2019

The simplest viruses are a nucleoprotein that consists of nucleic acid (RNA or DNA) and capsid- protein coat. More complex viruses have an additional lipid membrane. There is a type of viruses - bacteriophages, which have a special structure that allows them to introduce their genome into bacterial cells. Bacteriophages have a body consisting of a head with a genome, a tail (the tube that transports the genome into a cell), and processes.

Viruses can enter the cell by dissolving the cell membrane or by immersing membrane fragments together with the virus into the cytoplasm or together with pinocytic vesicles.

Once in the cell, the virus begins to multiply with the help of the cell, which synthesizes the DNA or RNA of the virus. The cell is damaged, and then dies, and viruses are able to infect other cells. Thus, the virus can exist and multiply almost indefinitely. There are a huge number of different viruses that cause dangerous diseases: flu, hepatitis, AIDS and others.

The most dangerous and unexplored to the end is human immunodeficiency virus (HIV) which causes acquired immunodeficiency syndrome ( AIDS), which enters the body through sexual contact or through the blood. This virus infects the cells of a person's immune system, making him vulnerable to any disease, due to which a person can die even from a cold.

Viruses that infect humans and animals have the ability to mutate and multiply very quickly. This fact makes viral diseases extremely resistant to treatment.

Acellular infectious agent. It has a genome (DNA or RNA), but lacks its own synthesizing apparatus. It is capable of reproducing only when it gets into the cells of more highly organized creatures. Reproducing, it damages the cells in which this process takes place.

Each of us is faced with viruses many times in our lives. After all, it is they that cause most of the cases of seasonal colds. The body successfully copes with the usual ARVI itself - our immunity can withstand the attacks of infections. But not all viral diseases are so harmless. On the contrary, some of them can lead to serious damage to tissues and systems, cause severe chronic diseases, become the cause of disability and even death. How to understand the variety of viruses? How to protect yourself from the most dangerous? And what if the disease has already been detected? What are antibodies to the virus and which ones appear during the disease?

Human Viruses

To date, more than 5 thousand different viruses have been described, but it is assumed that there are millions of their species. They are found in all ecosystems and are considered the most abundant biological form. Moreover, these infectious agents are capable of infecting animals and plants, bacteria and even archaea. Human viruses occupy a special place, because they cause the greatest number of diseases. Moreover, the diseases are very diverse in terms of their severity, prognosis and course.

At the same time, it is with viruses that an important condition of evolution is associated - horizontal gene transfer, in which genetic material is transmitted not to descendants, but to other types of organisms. In fact, the virus has contributed in no small measure to genetic diversity. For example, studies have shown that the human genome is 6-7% composed of various virus-like elements and their particles.

Virus in men

Human viruses are capable of equally infecting the organisms of children and adults, as well as representatives of both sexes. However, there are species that pose a particular danger to a certain category of the population. An example of a dangerous virus in men is the paramyxovirus, which causes mumps. Most often, the mumps passes without any particular complications, with a noticeable lesion of the salivary and parotid glands. However, the virus in men poses a great danger, since more often than in women, it also affects the sex glands, and is capable of causing orchitis in 68% of cases, an inflammation of the testicles. And this, in turn, can cause infertility. This complication is typical for adults and adolescents; in boys under 6 years of age, orchitis occurs only in 2% of cases. Also, the virus in men can provoke the development of prostatitis.

Paramyxovirus is highly contagious, transmitted by airborne droplets, including during the incubation period, when there are no symptoms of the disease yet. There is no specific treatment for mumps, so vaccination is the best protection against the disease. Mumps vaccination is included in the mandatory routine vaccination calendar in many countries.

Virus in women

Now special attention is focused on the human papillomavirus in women, because some of its types have been proven to be associated with the development of cervical cancer. In total, according to the World Health Organization, there are at least 13 such types, but the greatest danger is represented by the 16 and 18 types, which are characterized by the highest oncological risk. It is with these two viruses in the body that 70% of all cases of cervical cancer and precancerous conditions are associated.

At the same time, with timely diagnosis and removal of papillomas, such an outcome can be avoided. Cancer, as a complication of HPV, with normal immunity develops within 15-20 years, therefore, systematic examinations by a gynecologist will help in time to identify a dangerous virus in women of different ages. It should be said that a factor such as smoking affects the activity of the papilloma virus - it contributes to the degeneration of genital warts into a malignant neoplasm. Since there is no specific treatment for HPV, the World Health Organization recommends vaccination against types 16 and 18.

Viruses in women are especially dangerous during pregnancy, since, due to their small size, they easily penetrate the placental barrier. At the same time, the severity of the disease in the mother and the likelihood of fetal damage are not related. It often happens that latent or easily transferred viral infections cause serious pathologies in the fetus, can cause miscarriage.

It should be said that most viruses are dangerous only if a woman becomes infected with them during pregnancy. In this case, the mother's body does not have time to develop enough antibodies to protect the fetus, and the virus causes serious damage.

The most dangerous is early pregnancy, up to 12 weeks, since it is now that embryonic tissues are being formed, which are most easily affected by viruses. In the future, the risk of complications decreases.

Viruses transmitted through blood and its components, as well as other biological fluids, are dangerous directly during childbirth. Because the baby can become infected with them, passing through the birth canal.

The most dangerous viruses in women during pregnancy:

• Rubella virus.

In the first trimester of pregnancy, the likelihood of fetal damage is 80%. After 16 weeks, the risk of injury decreases significantly, and most often pathologies manifest themselves only as deafness. In the early stages, the virus can cause bone damage, deformity, blindness, heart defects, and brain damage in the fetus.

• Herpes virus 1 (HSV-1) and 2 (HSV-2) types.

The most dangerous is the second, genital type, with which a child can become infected during the passage of the birth canal. In this case, the development of severe neurological damage is possible, among which the most dangerous is encephalitis. In some cases, herpes simplex virus type 2 can kill a child. HSV-1 is asymptomatic, most often easily tolerated by the fetus and does not cause significant harm to health.

Infection of the mother at an early stage can lead to the development of fetal pathologies incompatible with life, as a result of which a miscarriage will occur. In addition, the disease is dangerous not only by the effect of the virus itself, but also by the general intoxication of the body. It, in turn, can cause fetal hypoxia, developmental delay, and more. That is why WHO recommends that pregnant women get vaccinated against influenza, especially during an epidemically dangerous period.

Botkin's disease (hepatitis A) is very often carried over in childhood, so it is quite rare during pregnancy. However, if the infection does occur, the disease will be severe. Hepatitis B and C can pose a threat to an unborn child, especially if a woman contracted them during pregnancy. Chronic hepatitis B and C are dangerous during childbirth. Most often, it is the hepatitis B virus that is transmitted in this way. Moreover, in congenital form, it is much more difficult to treat and in 90% of cases becomes a chronic incurable form. Therefore, women planning a pregnancy may be advised to be vaccinated against hepatitis B. If there is a chronic infection, then it is worth having a cesarean section. The hepatitis E virus rarely poses a serious danger, but it is during pregnancy that it can lead to serious consequences for the fetus and the woman herself. Including cause death from kidney failure.

Most often, infection occurs in childhood, after which a person is a carrier of the virus, while no symptoms appear. Therefore, as a rule, by the time of pregnancy, this virus in women does not pose a particular danger. In the event that infection with cytomegalovirus occurred during the gestation of a child, the fetus in 7% of cases can get complications in the form of cerebral palsy, hearing loss, etc.

The human body develops specific immunity to various viruses that it encounters throughout life. This explains the fact that a child suffers from ARVI (acute respiratory viral infections) more often than an adult. The frequency of infection with the virus is the same at different ages, but in an adult, the immune system suppresses the infectious agent even before symptoms appear. In domestic pediatrics, there is the concept of "frequently ill child", that is, one who carries more than 5 ARVI per year. However, foreign doctors believe that 6 infections per year are the norm for children under 3 years old. And a child attending kindergarten can carry up to 10 colds annually. If acute respiratory viral infections pass without complications, they should not cause concern, - the well-known pediatrician Yevgeny Komarovsky believes.

Also, childhood is characterized by a number of certain viral infections that are extremely rare in adults. Among them:

• Chickenpox.
• Measles.
• Rubella.
• Mumps.

It should be noted that children of the first year of life are practically not susceptible to these diseases, since even in the womb they receive antibodies to viruses from the mother's blood through the placenta.

Despite the fact that these infections are most often easily tolerated by children, there is still a risk of complications. For example, measles often leads to pneumonia and is one of the leading causes of infant mortality, while mumps causes inflammation in the genitals. Therefore, there are effective vaccinations against all of the above viral infections - timely immunization makes it possible to obtain immunity without a previous illness.

Virus as a form of life

Also, these non-cellular infectious agents, this is how viruses are now characterized, lack basic and energy metabolism. They cannot synthesize protein, as other living organisms do, and outside the cell they behave like a particle of a biopolymer, not a microorganism. The virus outside the cell is called the virion. It is a structurally complete viral particle that is capable of infecting the host cell. When infected, the virion is activated, forms a "virus-cell" complex and it is in this state that it is able to multiply, while transmitting its genetic code to new virions.

Viruses, like other living organisms, can evolve by natural selection. It is due to this that some of them, for example the influenza virus, are capable of constantly causing epidemics, since the developed immunity against new forms does not work.

The virion size is 20-300 nm. Thus, viruses are the smallest infectious agents. For comparison, bacteria are on average 0.5-5 microns in size.

As already mentioned, the virus differs in that it can multiply and is active only inside a living cell. Most types of viruses completely penetrate the cell, but there are those that introduce only their genome into it.

The life cycle of this extracellular agent can be divided into several stages:

• Attachment.

Moreover, it is at this stage that the circle of hosts of the virus is determined, because often these are highly specialized microorganisms that are able to interact only with certain types of cells. Thus, viruses that cause respiratory diseases prefer cells of the mucous membranes of the respiratory tract, and HIV is able to interact only with a specific type of human leukocytes.

• Penetration.

At this stage, the virus delivers its genetic material into the cell, which will later be used to create new virions. Viruses are able to multiply in different parts of the cell, some use the cytoplasm for these purposes, others use the nucleus.

• Replication is the reproduction of copies of the genetic material of a virus.

This process is only possible inside the cell.

• The release of virions from the host cell.

In this case, the membrane and the cell wall are damaged, and the cell itself dies. However, in some cases, viruses remain in the cell without damaging it and multiplying with it. Infected cells can exist for a long time, and the disease itself does not make itself felt, turning into a chronic form. This behavior is typical, for example, for the herpes virus, papillomavirus and others.

Virus genome: DNA-containing and RNA-containing

Depending on the form in which the genetic material of viruses is contained, they are usually divided into DNA-containing and RNA-containing (Baltimore classification).

• DNA viruses.

Their replication (reproduction) occurs in the cell nucleus, and the process of forming new virions in most cases is completely provided by the synthetic apparatus of the cell.

• RNA viruses.

A large group that mainly multiplies in the cytoplasm of the cell. Among the RNA-containing agents, it should be noted separately about retroviruses, which differ from others in that they are able to integrate into the host cell's DNA. These viruses are often distinguished into a separate group for their unique property of reverse transcription. In normal genome replication, information is transferred from DNA to RNA, and retroviruses are able to make double-stranded DNA based on single-stranded RNA.

Depending on how active the virus is and how destructive the genetic material is for the cell, its effect on it also depends. For example, one of the most dangerous infections, HIV, is referred to as retroviruses. On the other hand, it is this kind of integration into the genome of a living cell that allowed some types of this type of virus to gain a foothold in DNA - with them scientists associate the species diversity of living organisms, as well as evolutionary processes.

Types of viruses

Viruses, despite their small size and dependence on the cell, still know how to protect the genetic material they carry. It is for this, first of all, that the shells of the virus are responsible. Therefore, viruses are sometimes classified according to their types.

Compared to other infectious agents, the structure of viruses is quite simple:

• Nucleic acid (RNA or DNA).
• Protein coat (capsid).
• Sheath (supercapsid). Not found in all types of viruses.

Virus capsid

The outer shell is made up of proteins and serves as a protective function of the genetic material. It is the capsid that determines which types of cells the virion can attach to; the membrane is also responsible for the initial stages of cell infection - membrane rupture and penetration.

The structural unit of the capsid is a capsomere. While in a cell, the virus, by self-assembly, reproduces not only genetic material, but also a suitable protein coat.

In total, 4 types of capsids are distinguished, which are easy to distinguish by shape:

• Spiral - capsomeres of the same type surround single-stranded DNA or RNA of the virus along their entire length.
• Icosahedral - capsids with icosahedral symmetry, which sometimes resemble balls. This is the most common type of virus that can infect animal cells, and therefore infect humans.
• Oblong - one of the subspecies of the icosahedral capsid, but in this version it is slightly elongated along the line of symmetry.
• Complex - includes spiral and icosahedral types. It is rare.

Virus envelope

For additional protection, some types of viruses surround themselves with another envelope formed from the cell membrane. And if the capsid is formed inside the cell, then the supercapsid "captures" the virus, leaving the cell.

The presence of a shell, consisting essentially of a material related to the body, makes the virus less visible to the human immune system. This means that such vibrios are highly infectious, capable of being in the body longer than others like them. Examples of enveloped virions are HIV and influenza virus.

Virus infection

Signs of the presence of a virus in the body are highly dependent on its type. Some infections cause an acute course of the disease, pronounced characteristic symptoms. These include the influenza virus, measles, rubella. Others, on the contrary, may not appear for many years, while harming the body. This is how the hepatitis C virus, HIV and other dangerous infections behave. Sometimes their presence can only be detected by specific blood tests.

Virus Infection Methods

Since viruses are widespread and capable of infecting different cells of the human body, they have access to all the main routes of infection transmission:

• Aerogenic (airborne) - viruses are carried through the air, by coughing, sneezing or even simple conversation.

This route of transmission is typical for all acute respiratory viral infections, including influenza, as well as measles, rubella and other infections.

• Alimentary (fecal-oral) is a transmission route characteristic of the types of viruses that can accumulate in the intestines, excreted with feces, urine, and vomit.

Infection occurs through dirty water, poorly washed food, or dirty hands. Examples are hepatitis A and E, poliomyelitis. Such infections are often seasonal in nature - infection with the virus occurs in warm weather, in summer.

• Hematogenous (through blood and components) - the infection enters through wounds, microcracks in the skin.

Viruses transmitted in this way are dangerous during blood transfusion, surgery and other medical procedures, injection drug addiction, tattooing and even cosmetic procedures. Often, the infection is able to penetrate through other biological fluids - saliva, mucus, etc. The viruses of hepatitis B, C and D, HIV, rabies and others are transmitted through the blood.

• Transmissible - transmitted through insect and tick bites.

Among the most common diseases caused by such viruses are encephalitis and mosquito fever.

• Vertical - the virus is transmitted from mother to child during pregnancy or childbirth.

Most diseases with hematogenous transmission can be transmitted in this way. In the first trimester of pregnancy, rubella, influenza and other diseases are dangerous.

• Sexual - infection occurs through unprotected sexual intercourse.

The route of transmission is also typical for viruses transmitted through blood and components. According to WHO, four viral infections are most often transmitted in this way - HIV, herpes, papilloma virus, hepatitis B.

Not all viruses that enter the human body are capable of causing illness. Any foreign organism that comes to us immediately meets the cells of the immune system. And if a person has developed acquired immunity, then the antigens will be destroyed even before the symptoms of the disease develop. Our immune system provides stable protection, often for life, against many viruses - acquired immunity is developed after contact with the virus (illness, vaccination).

Some infections, such as measles, rubella, polio, can cause epidemics among children and practically do not affect the adult population. This is precisely due to the presence of acquired immunity. Moreover, if vaccination provides "collective immunity", such viruses will not be able to cause epidemics in children's collectives.

Some species, such as the flu virus, can mutate. That is, every season a new strain of the virus appears, for which the population has not developed immunity. Therefore, it is this infection that can cause annual epidemics and even pandemics - infection of the population of several countries or regions.

Among the most famous pandemics that humanity has experienced, different strains of influenza are quite common. These are, first of all, the "Spanish flu" of 1918-1919, which claimed 40-50 million lives, and the Asian flu of 1957-1958, during which about 70 thousand people died.

Smallpox viruses also caused pandemics, which in the twentieth century alone caused 300-500 million deaths. Thanks to mass vaccinations and revaccinations, this virus was defeated - the last case of infection was recorded in 1977.

The human immunodeficiency virus (HIV), which is also considered a pandemic disease in terms of prevalence, raises serious concerns.

Symptoms of the penetration of the virus into the body

Different viruses in the body behave differently, manifest their symptoms, and sometimes the disease is asymptomatic, without making itself felt for a long time. For example, hepatitis C most often does not manifest itself by external signs, and the disease is detected only in an advanced stage or by accident - according to blood tests. Influenza, on the contrary, is always acute, with an increase in temperature, general intoxication of the body. Measles and rubella are characterized by a specific skin rash.

There are viruses that are successfully suppressed by the immune system, but remain in the body. A classic example is herpes simplex, infection with which is life-long and incurable. However, the disease rarely causes serious inconvenience, manifesting only occasionally as ulcers on the lips, genitals and mucous membranes.

Many types of human papillomavirus occur with subtle symptoms, the infection does not require treatment and goes away on its own. However, there are HPVs that form that can degenerate into malignant neoplasms. Therefore, the appearance of any type of papilloma or condyloma is a reason to pass an analysis for viruses, which will help determine the type of infection.

Signs of a viral infection

Most often, we are faced with viruses that cause acute respiratory diseases. And here it is important to be able to distinguish them from diseases caused by bacteria, since the treatment in this case will be very different. SARS provoke more than 200 types of viruses, including rhinovirus, adenovirus, parainfluenza and others. However, despite this, infection with the virus still manifests itself with similar symptoms. ARVI is characterized by:

• Low subfebrile temperature (up to 37.5 ° C).
• Rhinitis and cough with clear mucus.
• Headaches, general weakness, poor appetite are possible.

Flu, which always begins acutely, within a few hours, is characterized by high fever, as well as general intoxication of the body - severe malaise, pain, often in muscles and joints, is distinguished by special symptoms. Human viruses that cause respiratory disease are usually active in the body for no more than a week. This means that approximately 3-5 days after the first symptoms, the patient feels a significant improvement in his condition.

With a bacterial infection, there is a strong fever, pain in the throat and chest, the discharge becomes greenish, yellow, thicker, and blood impurities can be observed. The immune system does not always successfully cope with bacteria, therefore, improvement in the condition in the first week of the disease may not be observed. Bacterial diseases of the respiratory tract can cause complications in the heart, lungs and other organs, so treatment should be started as soon as possible.

It is extremely difficult to identify a virus by symptoms alone. This is especially true of types of viruses that are similar in their effects on the body. For example, to date, about 80 human papillomaviruses have been studied. Some of them are quite safe, while others lead to the development of cancer. Hepatitis viruses, despite the fact that they affect the same organ, the liver, pose a different threat. Hepatitis A often goes away without complications, and the C virus, on the contrary, in 55-85%, according to the WHO, leads to the development of a chronic disease ending in liver cancer or cirrhosis. Therefore, if symptoms are detected or if an infection is suspected, it is necessary to pass tests that will help to accurately determine the type of virus.

Virus analysis

Among the tests that are used to detect viruses, the most popular are:

• Immunoassay blood test.

It is used to detect antigens and antibodies to them. In this case, there is both a qualitative (determination of the presence of a virus) and quantitative (determination of the number of virions) analysis. Also, this method will help determine the level of hormones, identify sexually transmitted infections, allergens, etc.

• Serological blood test.

It is used not only to determine an infectious disease, but also to establish its stage.

• Polymerase chain reaction (PCR method).

To date, the most accurate method that helps to identify even small fragments of foreign genetic material in the blood. Moreover, since this analysis for viruses determines the presence of the pathogen, and not the reaction to it (detection of antibodies), it can be carried out even during the incubation period of the disease, when there is still no noticeable immune response.

To diagnose viral infections, it is important to determine not only the infection itself, but also its amount in the blood. This is the so-called viral load - the amount of a specific type of virus in a specific volume of blood. It is thanks to this indicator that doctors determine the infectiousness of a person, the stage of the disease, can control the treatment process and check its effectiveness.

After the virus enters the human body, the immune system begins to produce specific immunoglobulins (Ig) - antibodies to a specific type of virus. It is by them that it is often possible to reliably determine a specific disease, the stage of the disease, and even the presence of a previous infection.

In humans, there are five classes of antibodies - IgG, IgA, IgM, IgD, IgE. However, in the analysis for the virus, two indicators are most often used:

• IgM - immunoglobulins, which are produced first when an infection enters. That is why their presence in the blood speaks of the acute stage of a viral infection. IgM are produced throughout the course of the disease, with primary infection or exacerbation. These are large enough immunoglobulins that, for example, cannot pass through the placental barrier. This explains the serious damage to the fetus by some viruses during the initial infection of a woman during pregnancy.
• IgG - antibodies to the virus, which are produced much later, in some diseases, already at the stage of recovery. These immunoglobulins are able to remain in the blood for life and thus provide immunity against a particular virus.

Antibody tests should be decoded as follows:

• IgM and IgG are absent. There is no immunity, the person has not encountered an infection, which means that primary infection is possible. When planning pregnancy, such indicators for certain viruses in women mean a risk group for developing a primary infection. In this case, vaccination is recommended.
• IgM is absent, IgG is present. The body has developed immunity to a specific virus.
• IgM is present, IgG is absent. There is an acute stage of infection, the virus is in the body for the first time.
• IgM and IgG are present. The end of the disease, or the exacerbation of a chronic process. The correct interpretation of such a virus test result depends on the amount of antibodies and can only be done by a doctor.

Types of viral infections

Viruses, like other antigens, cause an immune response - this is how the body copes with various foreign objects and microorganisms. However, some types of viruses are able to remain invisible for a long time to the immune system. It depends on this how long the disease will last, whether it will turn into a chronic form, and what harm it can inflict on the body.

Any viral disease begins with an acute stage. However, in some cases, after it, recovery occurs, and in others, the disease becomes chronic. Moreover, many diseases prone to chronicity are extremely weak in the acute period. Their symptoms are nonspecific, and sometimes they are completely absent. On the contrary, those diseases that the immune system successfully suppresses are characterized by severe symptoms.

Acute viral infections that do not become chronic include:

• ARVI, including influenza
• Rubella
• Parotitis
• Hepatitis A (Botkin's disease) and E
• Rotavirus infection (intestinal flu)
• Chickenpox

Persistent immunity is developed to the listed viruses in the human body. Therefore, diseases are transferred only once in a lifetime. The only exceptions are some forms of ARVI, in particular, influenza, the virus of which is actively mutating.

Chronic viral infections

A considerable number of viruses are characterized by a chronic course. Moreover, in some cases, if a virus is detected, then after the acute stage the person remains its lifelong carrier. That is, the infection does not pose a danger to human health and life. These viruses include:

• Epstein-Barr virus (in rare cases, it can cause infectious mononucleosis).
• Some types of human papillomavirus.
• Herpes simplex virus types 1 and 2.

All these viruses are potentially capable of causing quite serious damage to tissues and systems, but only if the immunity is significantly reduced. For example, with AIDS, some autoimmune diseases, as well as when taking certain medications, in particular, in the treatment of cancer.

Another group of viruses that can remain in the human body for life is dangerous even for people with a normally functioning immune system. Among the main infections of this kind:

• AIDS virus.

The period of infection and the first stage of the spread of the virus throughout the body is asymptomatic. However, 2-15 years after infection, a person develops acquired immunodeficiency syndrome (AIDS). It is the syndrome that is the cause of deaths among HIV-infected.

• Hepatitis C and B.

Hepatitis C in the acute stage is asymptomatic, and often (up to 85%) becomes chronic, which threatens with serious complications in the form of cancer or cirrhosis of the liver. However, today there are drugs that are quite effective in curing patients. Hepatitis B becomes chronic much less frequently, in no more than 10% of cases in adults. At the same time, there is no cure for this virus - chronic hepatitis B is not treated.

• Human papillomavirus with high cancer risk (types 16, 18 and others).

Some types of HPV are capable of provoking the development of malignant tumors, in particular, it is the human papillomavirus in women that causes 70% of all cases of cervical cancer. The virus in men can also manifest itself by the formation of warts of various types, but does not cause cancer.

To date, medicine has made significant progress in the treatment of viral infections, but this group of diseases is difficult to treat. In most cases, there are simply no effective drugs, and the treatment of viruses is reduced to symptomatic and supportive therapy.

What to do if a virus is found

The treatment strategy is determined by which virus is detected. For example, if we are talking about ARVI, childhood viral diseases (measles, rubella, mumps, baby roseola), the removal of symptoms will be an effective therapy. And only if they cause significant discomfort. So, for example, you can apply:

• Vasoconstrictor drops to relieve swelling in the nasal cavity.
• Antipyretic at high temperatures (from 37.5-38 ° C).
• Non-steroidal anti-inflammatory drugs that have a double effect - they lower the temperature and relieve pain (ibuprofen, paracetamol, aspirin).

Treatment of the influenza virus does not differ from the described scheme, however, since it is this infection that often causes severe complications, the patient must be under medical supervision. One of the most dangerous consequences is viral pneumonia, which develops on the 2-3rd day after the onset of the disease and can cause pulmonary edema and lead to death. Such pneumonia is treated exclusively in a hospital with the use of specific drugs (Oseltamivir and Zanamivir).

If human papillomavirus is detected, treatment is limited to supportive therapy and surgical removal of genital warts and warts.

With hepatitis C in the chronic stage, modern medicine uses direct-acting antiviral drugs (DPA). It is these drugs that WHO recommends today, as an alternative to interferons and Ribavirin, with which the disease was treated until recently.

People with HIV are prescribed antiretroviral therapy. If a virus is detected in the body, it cannot be completely eliminated, but thanks to treatment it is possible to keep it under control and also prevent the spread of the disease.

With an exacerbation of herpes infection, special medications can be taken, but they are effective only in the first 48 hours after the onset of symptoms. Their use later is impractical.

The basis of the fight against viruses in the body is human immunity. It is he who provides a successful cure for most of the known viruses, while others are able to neutralize, make them safe.

The immune system is quite complex and multi-stage. It is divided into innate and acquired immunity. The first provides non-specific protection, that is, it acts on all foreign objects in the same way. The acquired one appears after the immune system encounters a virus. As a result, a specific defense is developed that is effective in the event of a specific infection.

At the same time, some viruses in one way or another are able to resist the defense system and not cause an immune response. A striking example is HIV, which infects the cells of the immune system itself; these viruses are successfully isolated from them and block the production of antibodies.

Another example is neurotropic viruses that infect cells in the nervous system and the immune system simply cannot get to them. These infections include rabies and polio.

Congenital immunity

Congenital immunity is the body's reaction to any foreign biomaterial that occurs at the first contact with an infection. The reaction develops very quickly, however, unlike acquired immunity, this system recognizes the type of antigen worse.

Congenital immunity can be divided into components:

• Cellular immunity.

Most of it is provided by phagocyte cells capable of absorbing the virus, infected dying or dead cells. Phagocytosis is an important component of post-infectious immunity. In fact, it is phagocytes that are responsible for the effective cleansing of the body from foreign objects.

• Humonal immunity.

An important defense response to viral diseases is the body's ability to produce a specific protein, interferon. The affected cell begins to produce it as soon as the virus begins to multiply in it. Interferon is released from the infected cell and comes into contact with neighboring healthy cells. The protein itself has no effect on the virus, so infectious agents cannot develop a defense against it. However, it is interferon that can change unaffected cells in such a way that they suppress the synthesis of viral proteins, their assembly and even the release of virions. As a result, cells become immune to the virus, prevent it from multiplying and spreading throughout the body.

Acquired immunity

Acquired immunity is the ability to neutralize antigens that have already entered the body earlier. Distinguish between active and passive types of innate immunity. The first is formed after the body encounters a virus or bacterium. The second is passed on to the fetus or infant from the mother. Through the placenta during pregnancy and with breast milk during breastfeeding, antibodies from the mother's blood pass to the baby. Passive immunity provides protection for several months, active - often for life.

Acquired immunity, as well as innate immunity, can be divided into:

• Cellular immunity.

It is provided by T-lymphocytes (a subtype of leukocytes) - cells that are able to recognize viral fragments, attack and destroy them.

• Humonal immunity.

The ability of B-lymphocytes to produce antibodies to the virus (immunoglobulins), which neutralize specific antigens, allows the body to create specific defenses. An important function of humonal immunity is the ability to remember contact with an antigen. For this, specific IgG antibodies are produced, which are subsequently able to prevent the development of the disease if a virus is infected.

To date, a relatively small number of antiviral drugs with proven effectiveness are used in medicine. The entire spectrum of drugs can be divided into two groups:

1. Stimulating the human immune system.
2. Acting directly on the detected virus, the so-called direct-acting drugs.

The former can be called broad-spectrum drugs, but their treatment often has a number of serious complications. Interferons are one of these drugs. The most popular of them is interferon alpha-2b, which is used in the treatment of chronic forms of hepatitis B and was previously used for the hepatitis C virus. Interferons are quite difficult to tolerate by patients, often causing various side effects from the cardiovascular and central nervous system. They also impose pyrogenic properties - they cause fever.

The second group of antiviral drugs is more effective and easier to tolerate by patients. Among them, the most popular are medicines that treat:

• Herpes (Acyclovir drug).

Suppress the symptoms of viral disease, but cannot completely eliminate the virus.

• Flu.

On the recommendation of the WHO, inhibitors of influenza neuraminidase (Oseltamivir and Zanamivir) are now being used, since most modern strains of the influenza virus have resistance to their predecessors, adamants. The commercial names of the drugs are Tamiflu and Relenza.

• Hepatitis.

Until recently, Ribavirin in combination with interferons was actively used to treat hepatitis C and B. Now hepatitis C (genotype 1B) is treated with new generation medicines. In particular, since 2013, the direct-acting drug Simeprevir has been approved, which has shown high efficiency - 80-91% of a persistent virological response in different groups, including 60-80% in people with liver cirrhosis.

Unfortunately, drugs cannot completely eliminate the virus, but antiretroviral drugs give a fairly stable effect - the stage of remission begins, and the person becomes non-infectious to others. For HIV-positive people, antiretroviral therapy must be lifelong.

Prevention of viral diseases

Since there is no specific treatment for many viral diseases, but at the same time they pose a very real danger to human health and life, prevention comes to the fore.

Precautions

Many viral infections spread quickly and are highly contagious. When it comes to viruses transmitted by airborne droplets, an effective measure is the introduction of quarantine in preschool and school institutions. Because an infected child can spread the virus before symptoms appear, this is how the whole community can be prevented from getting the virus.

During an epidemically dangerous period, it is advisable to avoid large crowds of people, especially in closed rooms. This will reduce the risk of contracting various acute respiratory viral infections, including the flu.

Prevention of viruses transmitted by the fecal-oral route (for example, Botkin's disease and poliomyelitis) - washing hands, boiling water and using only proven water sources, thoroughly washing fruits and vegetables.

The most dangerous are viruses transmitted through blood and other biological fluids. Risk factors for infection for them are:

• Injection drug addiction.
• Cosmetic procedures and tattooing using non-disinfected instruments.
• The use of personal hygiene items of an infected person - nail scissors, toothbrush, razor, and more.
• Unprotected sex.
• Surgery, blood transfusion.

A person who is at risk of being infected with such diseases must be tested for antibodies to viruses, primarily HIV, hepatitis C and B. It is necessary to donate blood 4-5 weeks after the alleged infection.

Any precautions do not provide a 100% virus protection guarantee. To date, the most reasonable way to prevent viral infections is vaccination.

Pharmacists have developed vaccines that are effective against more than 30 different viruses. Among them:

• Measles.
• Rubella.
• Mumps.
• Chickenpox.
• Flu.
• Polio.
• Hepatitis B.
• Hepatitis A.
• Human papillomavirus 16 and 18 types.

It was with the help of mass vaccination that it was possible to defeat the two variola viruses, which caused epidemics and led to deaths and disability.

Since 1988, WHO has partnered with a number of public and private health sectors to launch the Global Polio Eradication Initiative. To date, it is with the help of mass immunization that it has been possible to reduce the number of cases of infection with the virus by 99%. As of 2016, polio is endemic (that is, one that does not go beyond the country) in only two countries - Afghanistan and Pakistan.

The following material is used in vaccines:

• Live but weakened microorganisms.
• Inactivated - killed viruses.
• Acellular - purified material, such as proteins or other parts of the antigen.
• Synthetic components.

In order to reduce the risk of complications, vaccination for some viruses takes place in several stages - first with inactivated material, and then with live material.

Some vaccines give immunity for life - resistant antibodies to the virus are produced. Others require revaccination - a booster shot after a certain time.

Viruses and diseases

Human viruses cause diseases of various severity and course. Some of them are encountered by most of the inhabitants of the earth, others are rare. In this section, we have collected the most famous viruses.

Adenovirus

Adenovirus was discovered in 1953, then it was discovered after surgery on the tonsils and adenoids. Today, science knows about 50-80 subspecies of this virus, and they all cause similar diseases. It is adenovirus that is a common cause of the development of acute respiratory viral infections, and in some cases can lead to intestinal diseases in children. Infection with the virus leads to damage to the cells of the mucous membranes of the upper respiratory tract, tonsils, eyes, bronchi.

• Transmission path.

Airborne (more than 90% of cases), fecal-oral.

• Virus symptoms.

The disease begins with a high fever, which can rise to 38 ° C. General intoxication appears - chills, pain in muscles, joints, temples, weakness. There is a reddening of the throat and inflammation of the laryngeal mucosa, as well as rhinitis. In case of eye damage - redness of the mucous membranes, itching, pain.

• Possible complications.

They rarely appear, a bacterial infection may join, which will cause pneumonia, otitis media, sinusitis.

• Treatment.

Symptomatic, the use of vitamins, antihistamines is permissible.

• Forecast.

Favorable, in the absence of concomitant diseases and immunodeficiency, the disease goes away on its own.

The influenza virus is perhaps the best known of all respiratory infections. It really differs from other acute respiratory viral infections both in symptoms and in possible complications.

It is the flu that often causes epidemics and pandemics, as the virus constantly mutates. At the same time, some strains are capable of leading to rather serious illnesses, often fatal. Every year, even in the absence of serious pandemics, according to WHO, from 250 thousand to 500 thousand people die in the world.

• Transmission path.

Airborne, the virus can also persist on the surfaces and hands of an infected person.

• Virus symptoms.

It always begins acutely - the temperature rises (sometimes up to 39 ° C), cough and rhinitis begin, the general condition worsens. The influenza virus causes severe intoxication of the body, which manifests itself in pain, general weakness, drowsiness, and loss of appetite.

• Possible complications.

Influenza more often than other acute respiratory viral infections leads to complications, most of which are associated with the addition of a bacterial infection - pneumonia, bronchitis, otitis media, sinusitis and other diseases. Intoxication leads to exacerbation of chronic diseases, including cardiovascular, diabetes, asthma. Influenza can also cause viral complications, which appear 2-3 days after the first symptoms. These are the most dangerous consequences of the disease, as they can lead to pulmonary edema, the development of encephalitis and meningitis. Temporary loss of hearing or smell may occur.

• Treatment.

In the normal course of the disease, the detected virus does not need specific treatment. With the development of viral complications, especially pneumonia, the drugs Oseltamivir and Zanamivir are used, the administration of interferons is possible.

• Forecast.

The greatest danger from influenza is for people over 65 years of age, as well as those who have concomitant diseases - diabetes mellitus, heart and lung diseases. It is among these categories that the virus is most often fatal. Also, infection with the influenza virus can be dangerous for pregnant women and children. Therefore, for people at risk, WHO recommends getting an annual vaccination.

Chickenpox (chickenpox) is caused by the human herpesvirus type 3 from a wide family of herpes viruses. This disease is typical for young children, the person who has undergone it gains immunity to the virus for life. In this case, the body's susceptibility is 100%. Therefore, if a person without acquired immunity contacts a sick person, he will definitely become infected. In adulthood, chickenpox can be more difficult to tolerate, and if the primary infection occurred in a pregnant woman, it can cause serious fetal damage (however, in a maximum of 2% of cases).

• Transmission path.

Airborne, while the virus is able to move with the air current at distances up to 20 m.

• Virus symptoms.

The main distinguishing feature of chickenpox is a specific blistering rash that spreads throughout the body, occurs on the mucous membranes. After the first symptoms, new bubbles form for another 2-5 days, in rare cases up to 9 days. They itch and itch. The onset of the disease is accompanied by a high fever, which is especially difficult in adults.

• Possible complications.

In childhood, chickenpox is easily tolerated, the infection goes away on its own without specific treatment. Particular attention should be paid to the rash, because if it is combed, a scar may form on the skin. Also, bursting vesicles and ulcers that have arisen in their place can be an entrance for a bacterial skin infection.

• Treatment.

There is no specific treatment, with chickenpox, treatment is symptomatic, in particular, prevention of skin infection is carried out. An effective vaccine has now been developed against the virus, which provides lifelong immunity.

• Forecast.

Favorable.

Herpes simplex virus

There are two types of herpes simplex virus. The first type most often causes ulcers on the lips and mucous membranes of the mouth. The second is genital lesions. A person who has contracted the herpes virus remains its carrier for life. This infection cannot be cured, but with normal immunity it can be asymptomatic. HSV belongs to neurotropic viruses, that is, after infection, it moves to nerve cells and there remains inaccessible to the immune system.

The greatest danger is posed by HSV-2, since, according to the WHO, it increases the risk of infection with the human immunodeficiency virus by 3 times.

• Transmission path.

HSV-1 is transmitted through oral contact, with saliva, during an exacerbation of the infection. HSV-2 is transmitted sexually and vertically.

• Virus symptoms.

HSV-1 is manifested from time to time by the formation of ulcers on the lips and mucous membranes. The frequency of such rashes depends on the person's immunity; in some cases, the carrier may not show the virus at all. HSV-2 is also often asymptomatic, sometimes manifested by rashes in the form of vesicles on the genitals and in the anal region.

• Possible complications.

The most dangerous type 2 virus in women is during pregnancy, since it can cause infection of the fetus and subsequent pathologies from the central nervous system and other organs.

• Treatment.

In case of exacerbations, the use of antiherpetic drugs, such as acyclovir, may be recommended to an infected person.

• Forecast.

In the absence of immunodeficiency, this infection does not lead to serious health problems.

The group of papilloma viruses combines more than 100 types of various extracellular agents. Despite the fact that they cause diseases that are similar in symptoms - neoplasms appear on the skin - the severity of the course of the disease depends on the type of infection, as well as the immune system of the infected person.

Human papillomavirus

Human papillomaviruses (HPV) are one of the most common infections in the world that can cause various lesions. Most species are harmless, show mild symptoms after infection and then go away without treatment. According to the WHO, 90% is completely cured within 2 years after infection.

However, the human papillomavirus is still under special control and is being studied in detail. This is due to the fact that today it has been proven that at least 13 types of human papillomavirus are capable of causing cancer. First of all, types 16 and 18 are dangerous.

• Transmission path.

Contact (through the skin with a neoplasm), sexual (for genital forms of the virus).

• Virus symptoms.

After infection, papillomas, condylomas and various warts form on the skin or mucous membranes. Depending on the type of HPV, they look different and occur on different parts of the body. So, for example, for some types (1, 2, 4), lesions of the feet are characteristic, the oral mucosa is attacked by viruses of types 13 and 32. Condylomas on the genitals arise under the influence of 6, 11, 16, 18 and other types.

• Possible complications.

The most dangerous complication is the transformation of the papilloma into a malignant tumor.

• Treatment.

There is no specific therapy. Viruses either go away on their own, or remain for life. Surgical removal of warts, genital warts and papillomas is recommended for people with severe symptoms.

• Forecast.

Overall favorable. Even HPV types with a high cancer risk can be controlled. The key to the successful suppression of human papillomavirus in women and men is timely diagnosis, which involves blood tests for antibodies.

Human papillomavirus in women

The relationship of some types of human papillomavirus in women with the development of cervical cancer has been proven. According to the WHO, 16 and 18 types cause 70% of all cases of this oncological disease.

At the same time, it takes an average of 15-20 years for a neoplasm to degenerate, if a woman does not have problems with immunity. For HIV-infected people, this interval may be 5 years. Local treatment can help prevent the development of infection, and this requires timely diagnosis. That is why women are recommended to undergo annual examinations by a gynecologist and be tested for papilloma viruses.

On the genitals, two types of genital warts develop - pointed and flat. The former most often provoke types of the virus 6 and 11. They are clearly visible, form on the external genitals, and rarely lead to cancer. Flat viruses are provoked by viruses of types 16 and 18. They are located on the internal genital organs, are less visible and have a high risk of cancer.

Today, vaccines have been developed for 16 and 18 HPVs, which WHO recommends to use at the age of 9-13 years. In the United States and some European countries, these vaccinations are included in the vaccination schedule.

Among all liver inflammations, diseases of a viral nature are most common. There are such types of hepatitis viruses - A, B, C, D and E. They differ in the mode of transmission, course of the disease and prognosis.

Hepatitis A and E

Viruses of this group differ from the rest in that they are not capable of causing chronic disease. In the vast majority of cases, a once transferred illness gives lifelong immunity. Therefore, Botkin's disease is characteristic of childhood.

• Transmission path.

Alimentary (fecal-oral), most often through contaminated water.

• Virus symptoms.

Hepatitis A and E is manifested by nausea, vomiting, pain in the liver, fever, loss of appetite. Darkening of urine and whiteness of feces are also characteristic. The disease includes an icteric period, in which, due to an increase in the level of bilirubin in the blood, the skin, mucous membranes, nail plates and sclera of the eyes acquire a yellow tint.

• Possible complications.

These liver inflammations are dangerous for people with immunodeficiency disorders and also during pregnancy. In case of infection with the virus during pregnancy, hepatitis A is much more difficult to carry, and hepatitis E can cause serious fetal abnormalities and, in some cases, the death of the mother.

• Treatment.

There is no specific treatment for hepatitis A and E viruses. The main therapy consists of supportive measures and adherence to a therapeutic diet. A vaccine has been developed against hepatitis A.

• Forecast.

Favorable. Hepatitis A and E viruses do not cause chronic disease. The infection goes away without treatment after a few weeks or months. In the future, the liver is able to fully recover.

Hepatitis B, C, D

Hepatitis B, C and D pose a great health hazard. They are prone to chronicity, especially type C, which leads to chronic disease in 55-85% of cases. The hepatitis D virus is particularly dangerous. This is a satellite virus, that is, one that is active only in the presence of virus B. It is he who significantly aggravates the course of the disease. And in some cases, coinfection leads to acute liver failure and death already in the acute period of the disease.

• Transmission path.

Hematogenous (through blood), sexual, vertical. Hepatitis B, which is sometimes called serum hepatitis, is especially contagious.

• Symptoms

Hepatitis B is acute with severe symptoms of liver damage - intoxication, nausea, loss of appetite, white feces, dark urine, jaundice. Hepatitis C in the acute stage in the vast majority of cases is asymptomatic. Moreover, it can remain invisible and chronic. A person guesses about the disease only at the critical stages of cirrhosis or liver cancer.

• Possible complications.

Both diseases can develop into chronic infections. Most often this occurs in the case of the hepatitis C virus. The chronization of hepatitis B depends on the patient's age. So, for example, in infants the probability of such a course is 80-90%, and for adults - less than 5%. Chronic hepatitis is dangerous by irreversible liver damage - cirrhosis, cancer, acute liver failure.

• Treatment.

Hepatitis B is treated in the acute period; in the chronic form, there is no specific therapy - lifelong maintenance drugs are prescribed. However, there is an effective vaccine against the B virus, which has been used since 1982. Modern pharmacological developments have made it possible to increase the percentage of the effectiveness of the treatment of chronic hepatitis C up to 90%. Currently, direct-acting antiviral drugs are used for this disease, which are taken for 12 weeks.

• Forecast.

Chronic hepatitis C can cause serious liver damage for 20 years after infection, in some cases for 5-7 years. The risk of developing cirrhosis is 15-30%. Hepatitis B is dangerous already in the acute period if the virus D is also present in the blood. Chronic hepatitis B can also cause serious liver damage.

Human Immunodeficiency Virus (HIV)

HIV is considered one of the most dangerous infections in the world today. It is ubiquitous; as of 2014, there were approximately 37 million infected people worldwide. HIV is a pandemic disease that differs from others in that it attacks the immune system itself. The virus is most dangerous in the final stage of the disease - with acquired immunodeficiency syndrome (AIDS). It is with such a diagnosis that other infections can become active in a person, a tendency to form malignant tumors appears, any minor illness gives serious complications. It is a strong decrease in immunity that is the cause of death from HIV.

• Transmission path.

Hematogenous, sexual.

• Symptoms

Until AIDS develops, it is asymptomatic. After there are manifestations of lowered immunity, in particular, viruses are activated, which practically do not manifest themselves in a healthy person. For example, the Epstein-Barr virus, cytomegalovirus. Other viruses (measles, rubella, influenza,) lead to serious injuries and the development of pathologies.

• Possible complications.

Associated with infections that a person has. With immunodeficiency, the risk of developing complications in any disease sometimes reaches 100%. Even some mild infections can be fatal.

• Treatment.

HIV cannot be completely cured. If a person becomes infected, the infection will remain with him for life. However, effective antiretroviral therapy has been developed that must be lifelong. Thanks to these drugs, HIV can be kept under control, preventing the development of AIDS. The viral load is reduced so much that the person receiving treatment is no longer infectious.

• Forecast.

With timely treatment started, HIV-positive people are able to live a fulfilling life. Without treatment, AIDS develops within 2-15 years and leads to the death of the patient.

Cytomegalovirus infection is often remembered in the context of diseases that are dangerous during pregnancy. It is for the fetus that this virus from the herpesvirus family can pose a serious threat. However, this happens only if a woman becomes infected while carrying a child. This happens quite rarely, because the majority of the population is exposed to the virus as early as childhood.

• Transmission path.

Through biological fluids - saliva, urine, semen, secretions, and also through breast milk.

• Virus symptoms.

In people without immunodeficiency, even in the acute period, it is asymptomatic. The fetus may develop various pathologies, in particular deafness. Primary infection with cytomegalovirus during pregnancy can lead to miscarriage.

• Possible complications.

It is extremely rare and only for risk groups.

• Treatment.

A vaccine has been developed against cytomegalovirus, which may be necessary for people with immunodeficiency, pregnant women without acquired immunity to the virus.

• Forecast.

Favorable.

Rabies virus

The rabies virus is a neurotropic virus, that is, those that are capable of infecting nerve cells. Being in the nervous system, it becomes inaccessible to the cells of the immune system, since the immune response acts only within the bloodstream. That is why infection with rabies without treatment is fatal.

• Transmission path.

Through the bites and saliva of infected animals. Most commonly transmitted from dogs.

• Virus symptoms.

After the incubation period, which lasts an average of 1-3 months, there is a slight increase in temperature, pain at the site of the bite, and insomnia. Later, convulsions, phobia and hydration, hallucinations, fear, aggression appear. The disease ends with muscle paralysis and breathing disorders.

• Possible complications.

If symptoms appear, rabies is fatal.

• Treatment.

Vaccination should be started immediately after a bite or possible contact with a rabid animal. Treatment for rabies virus consists of a course of post-exposure prophylaxis (PEP).

• Forecast.

With timely vaccination, it is favorable.

Poliomyelitis mainly affects children under 5 years of age. In most cases, it does not cause serious health effects, but 1 in 200 people infected with the virus will cause severe paralysis. In 5-10% of patients with complications, paralysis of the respiratory muscles also occurs, which leads to death.

Polio has now been virtually eradicated by vaccination. This disease remained endemic in two countries - Pakistan and Afghanistan.

• Transmission path.

Fecal-oral.

• Virus symptoms.

With the paralytic form of the course of the disease, the body temperature rises, a runny nose, nausea, and headache appear. Paralysis can develop over several hours, most often affecting the limbs.

• Possible complications.

Muscle atrophy, deformity of the trunk, persistent paralysis of the limbs that remain for life.

• Treatment.

There is no specific treatment. At the same time, vaccination against poliomyelitis completely eliminates the risk of infection.

• Forecast.

Due to the immunization of the population, the number of pathologies caused by poliomyelitis has decreased by 99% since 1988.

Research history

For the first time, the existence of a virus (as a new type of pathogen) was proved in 1892 by the Russian scientist D.I.Ivanovsky and others. After many years of research on diseases of tobacco plants, in a work dated 1892, DI Ivanovsky comes to the conclusion that tobacco mosaic is caused by "bacteria passing through the Chamberlain filter, which, however, are not able to grow on artificial substrates."

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

In subsequent years, the study of viruses played an important role in the development of epidemiology, immunology, molecular genetics, and other branches of biology. Thus, the Hershey-Chase experiment became decisive evidence of the role of DNA in the transmission of hereditary properties. Over the years, at least six more Nobel Prizes in Physiology or Medicine and three Nobel Prizes in Chemistry were awarded for research directly related to the study of viruses.

Structure

Simply organized viruses are composed of a nucleic acid and several proteins that form an envelope around it - capsid... An example of such viruses is the tobacco mosaic virus. Its capsid contains one type of protein with a small molecular weight. Complexly organized viruses have an additional envelope - protein or lipoprotein; sometimes in the outer shells of complex viruses, in addition to proteins, carbohydrates are contained. The causative agents of influenza and herpes are examples of complexly organized viruses. Their outer membrane is a fragment of the nuclear or cytoplasmic membrane of the host cell, from which the virus enters the extracellular environment.

The role of viruses in the biosphere

Viruses are one of the most widespread forms of the existence of organic matter on the planet in terms of numbers: the waters of the oceans contain a colossal number of bacteriophages (about 250 million particles per milliliter of water), their total number in the ocean is about 4 10 30, and the number of viruses (bacteriophages) in ocean bottom sediments practically does not depend on depth and is very high everywhere. Hundreds of thousands of species (strains) of viruses live in the ocean, the overwhelming majority of which have not been described, much less studied. Viruses play an important role in the regulation of the population size of some species of living organisms (for example, the wildness virus reduces the number of Arctic foxes several times over a period of several years).

The position of viruses in the system of the living

Origin of viruses

Viruses are a collective group with no common ancestor. Currently, there are several hypotheses explaining the origin of viruses.

The origin of some RNA viruses is associated with viroids. Viroids are highly structured circular RNA fragments replicated by cellular RNA polymerase. It is believed that viroids are "escaped introns" - insignificant regions of mRNA cut out during splicing, which accidentally acquired the ability to replicate. Viroids do not encode proteins. It is believed that the acquisition of coding regions (open reading frame) by viroids led to the appearance of the first RNA-containing viruses. Indeed, examples of viruses containing pronounced viroid-like regions (hepatitis Delta virus) are known.

Examples of structures of icosahedral virions.
A. Virus that does not have a lipid envelope (eg, picornavirus).
B. An enveloped virus (eg herpesvirus).
The numbers indicate: (1) capsid, (2) genomic nucleic acid, (3) capsomere, (4) nucleocapsid, (5) virion, (6) lipid envelope, (7) membrane proteins of the envelope.

Detachment ( -virales) Family ( -viridae) Subfamily ( -virinae) Genus ( -virus) View ( -virus)

Baltimore classification

Nobel laureate biologist David Baltimore proposed his own scheme for classifying viruses based on differences in the mechanism of mRNA production. This system includes seven main groups:

• (I) Viruses containing double-stranded DNA and lacking an RNA stage (for example, herpes viruses, poxviruses, papovaviruses, mimivirus).
• (Ii) Viruses containing double-stranded RNA (eg, rotaviruses).
• (III) Viruses containing a single-stranded DNA molecule (eg parvoviruses).
• (Iv) Viruses containing a single-stranded RNA molecule of positive polarity (eg, picornaviruses, flaviviruses).
• (V) Viruses containing a single-stranded RNA molecule of negative or double polarity (eg, orthomyxoviruses, filoviruses).
• (VI) Viruses containing a single-stranded RNA molecule and having in their 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, for the classification of viruses, both systems are used simultaneously, as complementary to each other.

Further division is made on the basis of such traits as the structure of the genome (the presence of segments, a circular or linear molecule), genetic similarity with other viruses, the presence of a lipid membrane, taxonomic affiliation of the host organism, and so on.

Viruses in popular culture

In literature

• S.T.A.L.K.E.R. (fantasy novel)

In cinema

• Resident Evil ”and its sequels.
• In the sci-fi horror film 28 Days Later and its sequels.
• In the plot of the disaster film "Epidemic" there is a fictional "motaba" virus, the description of which resembles the real Ebola virus.
• In the movie "Welcome to Zombieland".
• In the movie "Purple Ball".
• In the film "Carriers".
• In the film "I Am Legend".
• In the film "Contagion".
• In the film "Report".
• In the film "Quarantine".
• In the movie "Quarantine 2: Terminal".
• In the series "Regenesis".
• In the TV series The Walking Dead.
• In the TV series "Closed School".
• In the film "Carriers".

In animation

In recent years, viruses have often become "heroes" of cartoons and animated series, among which should be named, for example, "Osmosis Jones" (USA), 2001), "Ozzy and Dricks" (USA, 2002-2004) and "Virus Attacks" (Italy, 2011).

Notes (edit)

1. In English . In Latin, the question of the plural of a given word is controversial. The word lat. virus belongs to a rare variety of the II declension, words of the neuter genus in -us: Nom.Acc.Voc. virus, Gen. viri, Dat. Abl. viro. Lat is also inclined. vulgus and lat. pelagus; in classical Latin, the plural is fixed only in the latter: lat. pelage, a form of ancient Greek origin, where η<εα.
2. Taxonomy of viruses on the website of the International Committee on Taxonomy of Viruses (ICTV).
3. (English))
4. Cello J, Paul AV, Wimmer E (2002). Chemical synthesis of poliovirus cDNA: generation of infectious virus in the absence of natural template. Science 297 (5583): 1016-8. DOI: 10.1126 / science.1072266. PMID 12114528.
5. Bergh O, Børsheim KY, Bratbak G, Heldal M (August 1989). "High abundance of viruses found in aquatic environments." Nature 340 (6233): 467-8. DOI: 10.1038 / 340467a0. PMID 2755508.
6. Elements - science news: By destroying bacterial cells, viruses actively participate in the circulation of substances in the depths of the ocean

Structure

Examples of structures of icosahedral virions.
A. Virus that does not have a lipid envelope (eg, picornavirus).
B. An enveloped virus (eg herpesvirus).
The numbers indicate: (1) capsid, (2) genomic nucleic acid, (3) capsomere, (4) nucleocapsid, (5) virion, (6) lipid envelope, (7) membrane proteins of the envelope.

Classification

Detachment ( -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 containing double-stranded DNA and lacking an RNA stage (for example, herpes viruses, poxviruses, papovaviruses, mimivirus).

• (Ii) Viruses containing double-stranded RNA (eg, rotaviruses).

• (III) Viruses containing a single-stranded DNA molecule (eg parvoviruses).

• (Iv) Viruses containing a single-stranded RNA molecule of positive polarity (eg, picornaviruses, flaviviruses).

• (V) Viruses containing a single-stranded RNA molecule of negative or double polarity (eg, orthomyxoviruses, filoviruses).

• (VI) Viruses containing a single-stranded RNA molecule and having in their 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 carried out on the basis of such traits as the structure of the genome (the presence of segments, a circular or linear molecule), genetic similarity with other viruses, the presence of a lipid membrane, taxonomic affiliation of the host organism, and so on.

History

The use of viruses

Links

• "Viruses hit the Nobel committee" Article. Newspaper "Kommersant" No. 181 (3998) dated 07.10.2008.

Literature

• Mayo M.A., Pringle C.R. Virus taxonomy - 1997 // Journal of General Virology... - 1998. - No. 79. - S. 649-657.