Human viruses and brief information about them. Viruses

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 transmitted 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 is 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 a large number of cells die, 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

The types of viruses in biology that can affect human health are 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 of control is vaccination, which creates immunity to infections, as well as antiviral drugs that can selectively inhibit viral replication.

Biology describes viruses and bacteria mainly as harmful inhabitants of the 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.

Preventative measures against viral diseases should be carried out in a timely and efficient manner. To do this, humanity must lead a healthy lifestyle and try in every possible way to increase 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

At the moment, extracellular agents can “boast” of the largest number of 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 main 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.

Some infections are asymptomatic or latent. In latent infection, viral RNA or DNA is present in the cell but does not cause disease unless triggering factors occur. Latency makes it easier for the virus to spread from person to person. Herpes viruses exhibit the property of latency.

Hundreds of viruses can infect humans. Viruses that infect people are spread primarily by the person themselves, mainly through secretions from the respiratory tract and intestines, some through sexual contact and blood transfusions. Their spread among people is limited by congenital immunity, acquired natural or artificial immunity, sanitary, hygienic and other social measures, as well as chemoprophylaxis.

For many viruses, animals are the primary host, with humans being only a secondary or incidental host. Zoonotic agents, in contrast to specific human viruses, are limited in their distribution geographically by those conditions in which the natural cycle of infection is maintained without human intervention (the presence of corresponding vertebrates, arthropods, or both).

The oncogenic properties of a number of animal viruses have been well studied. Human T-lymphotropic viruses type 1 are associated with some leukemias and lymphomas, and Epstein-Barr virus causes malignancies such as nasopharyngeal carcinoma, African Burkitt's lymphoma, and lymphomas in immunosuppressant-treated organ transplant recipients. Hepatitis B and C predispose to the development of hepatocarcinoma. Human herpes virus type 8 predisposes to the development of Kaposi's sarcoma, primary effusion lymphoma (body cavity lymphoma), and Castleman's disease (lymphoproliferative disorders).

The long incubation period characteristic of some viral infections gives rise to the term “slow viruses.” A number of chronic degenerative diseases of previously unknown etiology are now classified as slow viral infections. Among them, we note subacute sclerosing panencephalitis (measles virus), progressive rubella panencephalitis and progressive multifocal leukoencephalopathy (JC viruses). Creutzfeldt-Jakob disease and spongiform encephalopathy have features similar to slow viral infections but are caused by prions.

Diagnostics

Only a few viral diseases, such as measles, rubella, roseola neonatorum, erythema infectiosum, influenza and chickenpox, can be diagnosed based on clinical presentation and epidemiological data alone.

It should be remembered that accurate diagnosis is necessary when specific treatment is required or when an infectious agent poses a potential threat to society (for example, SARS).

Rapid diagnosis is possible in specially equipped virology laboratories by cultivation, PCR, and determination of viral antigens. Electron (not light) microscopy can help. For a number of rare diseases (for example, rabies, eastern equine encephalitis, etc.) there are specialized laboratories (centers).

Prevention and treatment

Antiviral drugs.

Progress in the use of viral drugs is very rapid. Antiviral chemotherapy targets different phases of viral replication. They can affect the attachment of the particle to the host cell membrane or interfere with the release of viral nucleic acids, inhibit the cellular receptor or viral replication factors, block specific viral enzymes and proteins necessary for viral replication, but do not affect the metabolism of the host cell. Antiviral drugs are most often used for therapeutic and prophylactic purposes against herpes viruses (including cytomegalovirus), respiratory viruses, and HIV. However, certain drugs are effective against many types of viruses, for example, anti-HIV drugs are used to treat hepatitis B.

Interferons.

Interferons are released from infected viruses or other antigens. There are many different interferons that exhibit multiple effects, including inhibition of viral RNA translation and transcription, and termination of viral replication without impairing host cell function. Interferons are sometimes given in a form bound to polyethylene glycol (pegylated interferons), which allows for a longer-lasting effect.

Interferon therapy is used to treat hepatitis B and C and human papillomavirus. Interferons are indicated for the treatment of patients with chronic hepatitis B, C in combination with impaired liver function, a certain viral load and the presence of an appropriate histological picture. Interferon-2b is used to treat hepatitis B at a dose of 5 million units subcutaneously once a day or 10 million units subcutaneously 3 times a week for 16 weeks. Treatment enhances the clearance of hepatitis B virus DNA and nBeAg from plasma, improves liver function and histological picture.

Hepatitis C is treated with ribavirin in combination with pegylated interferon-2b at a dose of 1.5 mcg/kg subcutaneously once a week or pegylated interferon-2a 180 mcg subcutaneously once a week. Treatment can reduce the level of viral RNA, improve liver function and histological appearance. Interferon-p3 intramuscularly or directly into the affected area is used in the treatment of genital warts of the genitals and skin. The optimal regimen and duration of effect are unknown. The effectiveness of the use of recombinant forms of endogenous interferon alpha in hairy cell leukemia, Kaposi's sarcoma, human papillomavirus and respiratory viruses is being studied.

Side effects include fever, chills, myalgia, weakness, begin 7-12 hours after the first injection and last up to 12 hours. There may also be depression, hepatitis and, if high doses are used, bone marrow suppression.

Vaccines and immunoglobulins.

Vaccines stimulate natural immunity. Viral vaccines are used against influenza, measles, mumps, polio, rabies, rubella, hepatitis B and A, shingles and yellow fever. Vaccines against adenovirus and varicella are available, but they are used only in high-risk groups (eg, military conscripts).

Immunoglobulins are used for passive immunization in a limited number of cases, for example, for post-exposure prophylaxis (hepatitis, rabies). Others may be useful in treating diseases.

Respiratory viruses

Viral infections most often affect the upper and lower respiratory tract. Respiratory infections can be classified according to the virus that causes them (eg, influenza), but usually a clinical syndromic classification is used (eg, colds, bronchiolitis, croup). Although individual pathogens have specific clinical symptoms (eg, rhinovirus and the common cold, respiratory syncytial virus and bronchiolitis), each virus can cause virtually any symptom.

The severity of viral infection varies widely, with it being more severe in children and the elderly. Mortality is determined by direct causes (depending on the nature of the viral infection), as well as indirect ones (as a result of exacerbations of concomitant cardiovascular pathology, bacterial superinfection of the lungs, paranasal sinuses, middle ear).

Laboratory testing of pathogens (PCR, culture, serological tests) takes too much time to be useful for a specific patient, but is necessary for analyzing the epidemic situation. More rapid laboratory testing is possible for influenza viruses and respiratory syncytial virus, but the value of these methods in routine practice remains unclear. Diagnosis is based on clinical and epidemiological data.

Treatment

Treatment of viral respiratory infections is usually symptomatic. Antibacterial agents are ineffective against viruses, and prophylaxis against secondary bacterial infections is not recommended: antibiotics are prescribed only for already existing bacterial infections. In patients with chronic pulmonary pathology, antibiotics are prescribed with fewer restrictions. Aspirin should not be used in children due to the high risk of developing Reye's syndrome. Some patients with viral upper respiratory illnesses have a cough that persists for many weeks after recovery. Symptoms may respond to bronchodilators and glucocorticoids.

In some cases, antiviral drugs are important. Amantadine, remantadine, oseltamavir and zanavir are effective against influenza. Ribavirin, a guanosine analogue, inhibits the replication of RNA and DNA of many viruses and can be prescribed to immunocompromised patients with rhinosyncytial lesions of the lower respiratory tract.

Cold

This is an acute viral infection of the respiratory tract, self-limiting and usually occurring without fever, with inflammation of the upper respiratory tract, including rhinorrhea, cough, and sore throat. The diagnosis is clinical. Prevention is helped by thorough hand washing. Treatment is symptomatic.

In most cases (30-50%), the causative agent is one of more than 100 serotypes of the rhinovirus group. Colds are also caused by viruses from the group of coronaviruses, influenza, parainfluenza, and respiratory syncytial, especially in patients undergoing reinfection.

The causative agents of colds have a connection with the time of year, most often it is spring and autumn, less often - winter. Rhinoviruses are most often spread through direct contact with an infected person, but can also be transmitted through airborne droplets.

For the development of infection, the most important thing is the presence in the serum and secretions of neutralizing specific antibodies, reflecting previous contact with this pathogen and providing relative immunity. Susceptibility to colds is not affected by the duration of cold exposure, the state of health and nutrition of a person, or pathology of the upper respiratory tract (for example, enlarged tonsils and adenoids).

Symptoms and diagnosis

The disease begins suddenly after a short incubation period (24-72 hours) with unpleasant sensations in the nose and throat, followed by sneezing, runny nose and malaise. The temperature usually remains normal, especially when the cause is rhinovirus and coronavirus. In the first days, nasal discharge is watery and profuse, then becomes thicker and purulent; The mucopurulent nature of these discharges is due to the presence of leukocytes (mainly granulocytes) and not necessarily a secondary bacterial infection. Coughing with scant sputum often continues for 2 weeks. If there are no complications, cold symptoms subside after 4-10 days. In chronic respiratory diseases (asthma and bronchitis), exacerbations usually occur after a cold. Purulent sputum and lower respiratory tract symptoms are not very characteristic of rhinovirus infection. Purulent sinusitis and inflammation of the middle ear are usually bacterial complications, but sometimes they are associated with a primary viral infection of the mucous membranes.

Diagnosis is usually clinical, without diagnostic tests. For differential diagnosis, allergic rhinitis is most important.

Treatment and prevention

There is no specific treatment. Antipyretics and analgesics are commonly used to reduce fever and relieve a sore throat. For nasal congestion, decongestants are used. Topical nasal decogestants are most effective, but their use for more than 3-5 days can lead to increased nasal discharge. To treat rhinorrhea, you can use first-generation antihistamines (for example, chlorpheniramide) or ipratropium bromide (0.03% intranasal solution 2-3 times a day). These drugs, however, should be avoided in the elderly and in those with benign prostatic hyperplasia and in those with glaucoma. First-generation antihistamines cause drowsiness, but second-generation (non-sedating) antihistamines are not effective in treating colds.

Zinc, echinacea, and vitamin C are widely used to treat colds, but their effects have not been proven.

There are no vaccines. Polyvalent bacterial vaccines, citrus fruits, vitamins, ultraviolet light, glycol aerosols and other folk remedies do not prevent colds. Hand washing and use of surface disinfectants reduce the prevalence of infection.

Antibiotics are prescribed only when a secondary bacterial infection occurs, with the exception of patients with chronic lung diseases.

Parainfluenza

Respiratory illnesses caused by several closely related viruses, ranging from the common cold to flu-like symptoms or pneumonia, and in severe forms with high fever, most often manifesting as influenza. The diagnosis is clinical. Treatment is symptomatic.

Parainfluenza viruses are RNA paramyxoviruses of four serologically distinct types, designated 1,2,3 and 4. These four serotypes cause disease of varying severity but share common antigens. Serotype 4 cross-reacts with antigenic determinants of mumps virus and can sometimes cause respiratory illness.

Limited outbreaks of parainfluenza occur in schools, nurseries, kindergartens, hospitals and other institutions. Serotypes 1 and 2 cause autumn outbreaks. The disease associated with serotype 3 is endemic and highly contagious in children under 1 year of age. Re-infection is possible, the severity of subsequent infections is reduced and their spread is limited. Thus, in immunocompetent individuals, the infection is more often asymptomatic.

The upper respiratory tract is most commonly affected in children, with or without low-grade fever.

When infected with parainfluenza virus type 1, croup (acute laryngotracheobronchitis) develops, mainly in children aged 6-36 months. Croup begins with cold symptoms, followed by fever and barking cough, hoarseness, and stridor. Respiratory failure is rare but can be fatal.

Parainfluenza virus type 3 can cause pneumonia and bronchiolitis in young children. The disease requires differential diagnosis with respiratory syncytial infection, but it is often weaker.

Specific laboratory diagnostics are not required. Treatment is symptomatic.

Respiratory syncytial and metapneumovirus infection

Respiratory syncytial virus (RSV) and human metapneumovirus (HMV) cause seasonal infection of the lower respiratory tract, especially in young children. The severity of the disease varies from asymptomatic to severe, and clinical manifestations include bronchiolitis and pneumonia. Diagnosis is usually clinical, although laboratory testing is available. Treatment is symptomatic.

RSV is an RNA virus classified as a pneumovirus and has subgroups A and B. Human metapneumovirus (HMV), a similar but distinct virus, was recently discovered. RSV is ubiquitous and almost all children are infected by the age of 4 years. Outbreaks of the disease usually occur in winter or early spring. The immunity of those who have recovered is unstable, so contagiousness reaches 40%. Still, the presence of antibodies against RSV reduces the severity of the disease. The epidemiological features of the spread of FMV are similar to RSV, but the severity of outbreaks is significantly lower. RSV is the most common cause of lower respiratory tract disease in young children.

Symptoms and diagnosis

The most characteristic symptoms are bronchiolitis and pneumonia. In typical cases, the disease begins with fever and respiratory symptoms that progress: after a few days, shortness of breath, coughing, and wheezing occur. In children younger than 6 months, apnea may be the first symptom. In healthy adults and older children, the disease usually occurs asymptomatically or as a fever-free cold. Severe disease develops in elderly, immunocompromised individuals suffering from concomitant pulmonary and cardiac pathologies.

RSV (possibly also CMV) should be suspected in young children with symptoms of bronchiolitis and pneumonia during the RSV season. Since antiviral treatment is generally not recommended, laboratory diagnostics are not needed. The latter is useful for in-hospital control, which makes it possible to identify groups of children affected by the same virus. Highly sensitive tests for detecting RSV antigens are available for children; They are insensitive towards adults.

Treatment and prevention

Treatment is symptomatic and includes oxygen inhalation and hydration therapy as needed. Glucocorticoids and bronchodilators are usually ineffective. Antibiotics are reserved for patients with ongoing fever and radiologically confirmed pneumonia. Palivizumab is ineffective for treatment. Ribaverine, which has antiviral activity, is ineffective or ineffective against RSV, is toxic and is not recommended for long-term use, except for immunocompromised individuals.

Passive prophylaxis with monoclonal antibodies to RSV (palivizumab) reduces hospitalization rates in high-risk adolescent populations. Economically, vaccination is justified for young children who may require hospitalization (that is, less than 2 years of age) with congenital heart defects or chronic lung diseases that required drug treatment in the last 6 months, premature infants (less than 29 weeks) who met the RSV season at the age of less than 1 year, or born in the period 29-32 weeks of gestation and who met the RSV season at the age of less than 6 months). The dose is 15 mg/kg intramuscularly. The first dose is prescribed only before the onset of exacerbation season. Subsequent doses are given at 1-month intervals throughout the entire epidemiological season, usually 5 doses.

Severe acute respiratory syndrome

Predictors of fatal outcomes are age over 60 years, severe concomitant pathology, increased LDH levels and an increase in the absolute number of neutrophils. Treatment of SARS is symptomatic, if necessary - mechanical ventilation. Oseltamivir, ribavirin and glucocorticoids can be used, but there is no data on their effectiveness.

Patients with suspected SARS should be hospitalized in a box with negative intrabox pressure. All measures to prevent transmission of infection through respiratory and contact routes must be taken. Personnel must wear N-95 masks, safety glasses, gloves, and gowns.

People who have been in contact with patients with SARS (eg, family members, flight attendants, medical personnel) should be alerted to the symptoms of the disease. If they have no symptoms, they can work, go to school, etc. If they develop fever or respiratory symptoms, they should limit their activities and be under medical supervision. If symptoms do not progress toward SARS within 72 hours, they can be considered tolerant.

>> human viral diseases

Viruses are the smallest forms of life that consist of a nucleic acid molecule, a carrier of genetic information, surrounded by a protective shell of proteins.

It is important to note that a living organism can be infected by several viruses at once. In such cases, genetic interaction between viruses and the emergence of a new recombinant form of the virus are possible. This, for example, explains the emergence of pandemic strains of the influenza virus, which are formed in the body of pigs infected simultaneously with the human and avian form of the influenza virus.

Clinical aspects of human viral diseases
Viruses play an important role in human life, as they can cause diseases of varying severity.

According to epidemiological characteristics, viral diseases are divided into anthroponotic, that is, those that only affect humans (for example, polio) and zooanthropotic, which are transmitted from animals to humans (for example, rabies).

The main routes of transmission of viral infection are:

1. The food route in which the virus enters the human body with contaminated food and water (viral hepatitis A, E, etc.)
2. Parenteral (or through the blood), in which virus enters directly into the blood or internal environment of a person. This mainly occurs when manipulating contaminated surgical instruments or syringes, during unprotected sexual intercourse, and also transplacentally from mother to child. Fragile viruses that quickly degrade in the environment (hepatitis B virus, HIV, rabies virus, etc.) are transmitted in this way.
3. The respiratory tract, which is characterized by an airborne transmission mechanism, in which the virus enters the human body along with inhaled air, which contains particles of sputum and mucus expelled by a sick person or animal. This is the most dangerous route of transmission, since the virus can be transported through the air over significant distances and cause entire epidemics. This is how influenza, parainfluenza, mumps, chickenpox, etc. viruses are transmitted.

Most viruses have a certain affinity for one or another organ. For example, hepatitis viruses multiply primarily in liver cells. Based on the type of target organs that are affected during a particular disease, we distinguish the following types of viral diseases: intestinal, respiratory (respiratory), affecting the central and peripheral nervous system, internal organs, skin and mucous membranes, blood vessels, immune system, etc.

Based on the type of clinical development, we distinguish between acute and chronic viral infections. The most common are acute viral diseases that occur with severe local symptoms (damage to the mucous membrane of the respiratory tract, damage to liver tissue, damage to various areas of the brain) and general symptoms - increased body temperature, weakness, pain in the joints and muscles, changes in blood composition and etc. Acute viral infection, as a rule, ends with complete recovery of the body. In some cases, the acute form of the disease becomes chronic. Chronic viral infections occur with a blurred clinical picture and sometimes may not be noticed by the patients themselves. Chronic infections are difficult to treat and can last a long time, leading to significant morphological and functional changes in internal organs (for example, chronic hepatitis B can lead to cirrhosis of the liver).

A separate type of viral infection is a latent infection, which is characterized by the prolonged presence of the virus in the body and the complete absence of symptoms of the disease. Under the influence of internal and external factors (hypothermia, decreased immunity), a latent infection can be activated and become acute.

Based on the location of the viral infection, we distinguish between local and generalized (general) viral infections. In local viral infections, the virus multiplies at the site of its entry into the body (for example, the mucous membrane of the respiratory tract) and does not penetrate into the internal environment of the body. This form of the disease is characterized by a short incubation period (the time from the moment the virus enters the body until the symptoms of the disease appear) and weak post-infectious immunity.

In generalized viral infections, the primary reproduction of the virus at the site of its entry into the body is replaced by the stage of penetration of the virus into the blood (viremia stage), with the current of which it spreads to various organs, where it causes secondary damage. Such infections are characterized by a long incubation period, and the immunity remaining after the illness, as a rule, protects the body for a long time from re-infection with the same virus.

Antiviral immunity
The penetration and reproduction of viruses in the human body causes a response from the immune system. The antiviral immune response consists of two components: humoral and cellular.

Humoral immunity mediated by specific antibodies that are produced by cells of the immune system in response to the presence of a virus in the body. In the first days of a viral infection, immunoglobulins (antibodies) of the IgM class are produced. In the following days, the secretion of IgM stops and they are replaced by antibodies of the IgG type, which have greater specificity and activity. Antibodies of the IgA type are also produced, which are released onto the surface of the mucous membranes and provide local protection against viruses. Determination of specific antibodies is an important diagnostic test that allows one to accurately determine the presence of a particular viral infection and assess the state of post-infectious immunity.

Cellular immunity carried out by T-lymphocytes and macrophages, which regulate the release of antibodies and destroy cells infected with the virus, thereby preventing its reproduction. After a viral infection, immune system cells remain in a person’s blood that “remember” the virus. When the same virus re-enters the body, these cells quickly recognize it and launch a powerful immune response - this is the essence of long-term post-infectious immunity.

However, the body’s immune response does not always bring only positive effects. Thus, with viral hepatitis B, excessive destruction of liver cells occurs precisely under the influence of activated T-lymphocytes, while the reproduction of the virus itself does not destroy liver cells.

HIV infection is characterized by profound suppression of the body's immune system. This happens because one of the targets of the virus is T-helper lymphocytes, the destruction of which leads to a complete suppression of the body's resistance.

The role of viruses in the occurrence of non-viral diseases
As mentioned above, the multiplication of the virus in the body leads to the development of one or another viral disease. However, the negative impact of viruses on the human body does not end there. In some cases, viruses cause diseases of a completely different nature.

It is now reliably known that the human papilloma virus causes cervical cancer. This occurs due to the fact that, penetrating the epithelium of the cervix, the virus activates genes responsible for the cancerous degeneration of normal cells.

In the pathogenesis of type 1 diabetes, an important role is played by viral infection, as a possible factor damaging the endocrine cells of the pancreas.

A number of pregnancy pathologies and fetal malformations are associated with various viral infections during pregnancy.

Literature:

The site provides reference information for informational purposes only. Diagnosis and treatment of diseases must be carried out under the supervision of a specialist. All drugs have contraindications. Consultation with a specialist is required!

All viruses are united in the kingdom Vira. Viruses are a unique group of infectious agents.

A complete viral particle - a virion - contains one or more molecules of DNA or RNA, surrounded by a protein shell, sometimes by other layers. These additional layers may be complex and contain carbohydrates, lipids, additional proteins and the like.

Viruses can exist in two forms: extracellular and intracellular. The virion, the extracellular form, has few or no enzymes and cannot replicate without a living cell. The intracellular form of the virus is in the form of a nucleic acid, which is capable of replicating and causing the metabolism of the host cell to produce virion components.

General properties of viruses that distinguish them from other living organisms:

• 1. Lack of cellular structure.
• 2. Inability to grow and divide independently.
• 3. Lack of own metabolic systems.
• 4. Contain only one type of nucleic acid - RNA or DNA.
• 5. Viruses require only nucleic acid to reproduce.
• 6. They do not reproduce outside the host cells.

Phytopathogenic viruses (plant viruses) cause various plant diseases: mosaic of tobacco, wheat, oats, soybeans; potato ring spot; dwarfism of tomato bushes, etc.

Zoopathogenic viruses. In humans and animals, viruses cause diseases such as smallpox, encephalitis, rabies, polio, influenza, the common cold, foot and mouth disease, and acquired immunodeficiency syndrome (AIDS). They are transmitted through direct contact with a patient, by airborne droplets, through insects and animals, and through blood.

Bacteriophages. Microbial viruses infect bacteria, actinomycetes, fungi and algae. There are hardly any bacteria for which a sufficiently conscientious search could not find a suitable phage. Scientists have tried to use phages to combat bacterial diseases, in particular to treat dysentery and staphylococcal infections, but the attempts did not produce the desired results. In the presence of blood, pus or feces, bacteriophages were inactive.