What viruses are: types, classification, characteristics, viral diseases, treatment and consequences. The history of computer viruses. The most terrible computer viruses in the history of the Internet

Doctors classify all infections as rapid and slow. The slower the bacteria, the more dangerous it is to human life. This is justified by the fact that these microorganisms have the greatest destructive factor and also do not have pronounced symptoms.

Let's look at the main infections:

• Herpetic. Herpes is present in the body of every person, but it worsens only if a provocateur appears. In appearance, herpes can be identified by characteristic blisters on one or another part of the patient’s body.
• Acute respiratory viral infection. This microbe enters the human respiratory tract and then infects them. The symptoms are similar to the flu or a common cold. The most dangerous part of the disease is the possibility of getting chronic bronchitis or pneumonia.
• Encephalitis. This microbe affects the human brain, which leads to the destruction of the central nervous system and consciousness. This disease has an extremely high mortality rate. Once infected, patients often fall into a coma, experience seizures and paralysis of some limbs. Also, this microbe contributes to the development of multiple organ failure, the result is death in 9 out of 10 cases.
• Hepatitis. Infection of the body with such a microbe leads to damage to the liver tissue. Subsequently, disturbances and complications in the functioning of this organ develop. These symptoms can lead to a disastrous outcome.
• Polio. After the disease, a person will experience constant convulsive attacks, and subsequently develop inflammation of the brain and loss of consciousness. As a result of these symptoms, paralysis is possible. The disease is extremely dangerous, as it leads to disability of the patient.
• Meningitis. This microorganism penetrates under the cerebral cortex and infects the cerebrospinal fluid. Subsequently, the virus “travels” throughout the human circulatory system. Can lead to disturbances of consciousness and atrophy of the muscles of the arms or legs, even despite correct therapy.
• Measles. After the onset of the disease, the patient develops a red rash on certain parts of the body, a cough and a fever. In itself, the microorganism is not particularly dangerous, but if you do not treat the infection in time, you can get complications in the form of encephalitis or meningitis.
• STD. Sexually transmitted diseases have been around for a long time. Previously, they were considered extremely dangerous, but with the current level of medicine, they can be completely cured. To completely eradicate the disease, symptoms must be identified in a timely manner.

History of research

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

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

In subsequent years, the study of viruses played a vital 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 have been awarded for research directly related to the study of viruses.

Structure

Simply organized viruses consist of a nucleic acid and several proteins that form a shell 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 shell - protein or lipoprotein; sometimes the outer shells of complex viruses contain carbohydrates in addition to proteins. Examples of complexly organized viruses are the pathogens of influenza and herpes. Their outer shell is a fragment of the nuclear or cytoplasmic membrane of the host cell, from which the virus exits into the extracellular environment.

The role of viruses in the biosphere

Viruses are one of the most common forms of existence of organic matter on the planet in terms of numbers: the waters of the world's 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 bottom sediments of the ocean practically does not depend on depth and is very high everywhere. The ocean is home to hundreds of thousands of species (strains) of viruses, the vast majority of which have not been described, much less studied. Viruses play an important role in regulating the population size of some species of living organisms (for example, the wilding virus reduces the number of arctic foxes several times over a period of several years).

The position of viruses in the living system

Origin of viruses

Viruses are a collective group that does not have a 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 that are replicated by the cell's RNA polymerase. It is believed that viroids are “escaped introns” - insignificant sections 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 viruses. Indeed, there are known examples of viruses containing pronounced viroid-like regions (hepatitis Delta virus).

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

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 that contain double-stranded DNA and do not have an RNA stage (for example, herpesviruses, poxviruses, papovaviruses, mimivirus).
• (II) Double-stranded RNA viruses (eg rotaviruses).
• (III) Viruses containing a single-stranded DNA molecule (eg, parvoviruses).
• (IV) Viruses containing a single-stranded RNA molecule of positive polarity (for example, picornaviruses, flaviviruses).
• (V) Viruses containing a single-stranded RNA molecule of negative or double polarity (for example, orthomyxoviruses, filoviruses).
• (VI) Viruses containing a single-stranded RNA molecule and having 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 made on the basis of such features as genome structure (presence of segments, circular or linear molecule), genetic similarity with other viruses, the presence of a lipid membrane, taxonomic affiliation of the host organism, and so on.

Viruses in popular culture

In literature

• S.T.A.L.K.E.R. (fantasy novel)

In cinema

• Resident Evil" and its sequels.
• In the science fiction horror film “28 Days Later” and its sequels.
• The plot of the disaster film "Epidemic" features a fictional virus "motaba", the description of which is reminiscent of the real Ebola virus.
• In the movie "Welcome to Zombieland".
• In the film "The Purple Ball".
• In the film "Carriers".
• In the film "I am Legend".
• In the movie "Contagion".
• In the film "Report".
• In the movie "Quarantine".
• In the movie "Quarantine 2: Terminal".
• In the series "Regenesis".
• In the television series "The Walking Dead".
• In the television series "Closed School".
• In the film "Carriers".

In animation

In recent years, viruses have often become the “heroes” of cartoons and animated series, among which are, for example, “Osmosis Jones” (USA), 2001), “Ozzy and Drix” (USA, 2002-2004) and “The Virus Attacks” (Italy, 2011).

Notes

1. In English. In Latin, the question of the plural of this word is controversial. The word is lat. virus belongs to a rare variety of the second declension, neuter words 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 at the International Committee on Taxonomy of Viruses (ICTV) website.
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

MINISTRY OF SCIENCE AND EDUCATION OF UKRAINE

Human viral diseases

Completed:

10th grade student

Secondary school No. 94

Gladkov Evgeniy

Checked by: Suprun Elena Viktorovna

Kharkov, 2004.

Diseases that are caused by viruses are easily transmitted from sick people to healthy people and spread quickly. Much evidence has accumulated that viruses are the cause of various chronic diseases.

These are smallpox, polio, rabies, viral hepatitis, influenza, AIDS, etc. Many viruses to which humans are sensitive infect animals and vice versa. In addition, some animals are carriers of human viruses without getting sick.

The main groups of viruses that cause diseases in humans are presented in the table:

Vaccination (inoculation, immunization) is the creation of artificial immunity to certain diseases. For this purpose, relatively harmless antigens (protein molecules) are used, which are part of microorganisms that cause diseases. Microorganisms can be viruses, such as measles, or bacteria.

Vaccination is one of the best means to protect children against infectious diseases that caused serious illness before vaccinations were available. Unfounded criticism of vaccination in the press was caused by the desire of journalists to inflate sensations from individual cases of post-vaccination complications. Yes, side effects are common to all medications, including vaccines. But the risk of getting a complication from vaccination is much less than the risk from the consequences of an infectious disease in unvaccinated children.

Vaccines stimulate the immune system to respond as if there were a real infection. The immune system then fights the “infection” and remembers the microorganism that caused it. Moreover, if the microbe enters the body again, it effectively fights it.

There are currently four different types of vaccines available:

biosynthetic vaccines; they contain substances obtained by genetic engineering methods that cause a reaction in the immune system. For example, hepatitis B vaccine, Haemophilus influenzae infection.

Smallpox is one of the oldest diseases. A description of smallpox was found in the Egyptian papyrus of Amenophis 1, compiled 4 thousand years BC. The causative agent of smallpox is a large, complex DNA-containing virus that multiplies in the cytoplasm of cells, where characteristic inclusions are formed. Smallpox is a particularly dangerous infectious disease, characterized by a severe course, fever, and a rash on the skin and mucous membranes, often leaving scars.

The source of infection is a sick person from the beginning of incubation until complete recovery. The virus dissipates with droplets of mucus and saliva during talking, coughing, sneezing, as well as with urine, sputum and crusts that fall off the skin. Infection of healthy people occurs through inhaled air and through the use of dishes, linen, clothing, household items, contaminated with the patient’s secretions.

Human smallpox has now been eradicated from the world through vaccination with smallpox vaccine.

Polio

Poliomyelitis is a viral disease that affects the gray matter of the central nervous system. The causative agent of polio is a small virus that does not have an outer shell and contains RNA. An effective method of combating this disease is the live polio vaccine. The main habitat of enteroviruses in nature is the human body, or rather the intestines, hence the name. The intestine is the only reservoir of many enteroviruses, from where viruses enter the blood, internal organs, and central nervous system.

POLIOMYELITIS (polios - gray, myelos - spinal cord). The name itself suggests that the virus affects the gray matter of the spinal cord. In paretic forms of polio, the motor innervation, which is responsible for muscle movement, is actually disrupted. Atrophic paralysis occurs, more often of the lower, less often of the upper extremities, depending on which segment of the spinal cord is affected. The disease is very serious and crippling. It has been known for a long time; Hippocrates mentions it. Unfortunately, polio is not uncommon.

The virus was discovered in 1945.

EPIDEMIOLOGY OF POLIOMYELITIS: Incubation period 7-14 days. Poliomyelitis is a highly contagious disease, the source is an asymptomatic sick person, the main route of transmission is fecal-oral. The fecal-oral route of transmission is the main route in countries with highly developed sanitary conditions. In countries with a highly developed sanitary culture, the leading route of transmission is airborne. In the first week of the disease, the virus can settle in the peripharyngeal lymph nodes and can be released into the environment through coughing and sneezing, infecting others

PATHOGENESIS. The pathogen enters through the mouth, often through dirty hands, dishes, and water. In a certain number of cases, the virus penetrates the intestinal barrier, enters the blood, and viremia occurs. In some cases, the virus penetrates the blood-brain barrier and enters the spinal cord, causing damage to the motor innervation. The polio pathogen can cause the following diseases:

aseptic meningitis

asymptomatic forms (inaparental form), when the virus is in the intestines without penetrating into the blood.

Abortive form (minor disease). The virus enters the blood, but cannot penetrate the blood-brain barrier. Clinically, this disease is manifested by sore throat and catarrh of the upper respiratory tract.

In a small number of children, the virus penetrates the blood-brain barrier and causes damage to the motor neurons of the anterior horns of the spinal cord, the so-called paralytic form. Mortality in the paralytic form is 10% and more than half of children experience permanent paralysis.

IMMUNITY for polio is lifelong, type-specific. The mechanism of immunity is determined by 2 main points:

Humoral general immunity is provided by immunoglobulins of class M and G2 circulating in the blood),

2. Local occurs in the tissue of the intestine and nasopharynx, pharynx, ensuring the stability of these tissues by the presence of secretory immunoglobulins of class A.

COXSACKIE VIRUSES. In the city of Coxsackie (America), in 1948, in a polio clinic, viruses were isolated from sick children that did not react with polyvalent polio serum. The isolated viruses were found to have the ability to cause diseases in newborn suckling mice. The division of Coxsackie viruses into 2 subgroups (A and B) is associated with their ability to infect the tissues of newborn mice differently.

Coxsackie viruses of subgroup A cause flaccid paralysis, and subgroup B cause spastic paralysis. Diseases caused by Coxsackie viruses: aseptic meningitis, sore throat, febrile diseases with rash.

Coxsackie viruses most often cause encephalomyocarditis in newborns.

ECHO VIRUSES. E - enteric, C - cytopathogenetic, O - orpham, H - human. In the process of studying enteroviruses, viruses were discovered that could not be classified as enteroviruses, since, firstly, they did not react with polio polyvalent serum, and secondly, they were not capable of causing diseases in suckling mice, so they could not be classified as Coxsackievirus. At first they were called orphans - orphans. Then ECHO. ECHO viruses cause aseptic meningitis, gastroenteritis in children, and febrile diseases with summer seasonality.

TREATMENT AND PREVENTION OF POLIOMYELITIS. There is no specific treatment for polio. There are no chemotherapy drugs or antibiotics that can help with the paralytic form. Symptomatic, restorative measures are possible.

There are 2 vaccines:

The Salk vaccine, developed in 1956 and called inactivated polio vaccine (IPV). This is a killed vaccine, it provides general humoral immunity, but does not protect the intestines. A person who is vaccinated with this vaccine will not get sick himself, but if a virus settles in that child’s intestines, he can become a carrier of the virus and infect others.

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 relevant 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 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 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 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% solution intranasally 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 in the form of 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 aged 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 must be taken to prevent transmission of infection by respiratory and contact routes. 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.

They are completely dependent on cells (bacteria, plant or animal) for reproduction. Viruses have an outer shell of protein and sometimes a lipid and a core of DNA or RNA. For infection to occur, the virus first attaches to a host cell. The viral DNA or RNA then enters the host cell and is separated from the outer envelope (viral cecapsulation) and replicated to the host cell using certain enzymes. Most RNA viruses copy their nucleic acid in the cytoplasm, while most DNA viruses copy it in the nucleus. The host cell typically dies, releasing new viruses that infect other host cells.

The consequences of viral infection vary widely. Many infections cause acute illness after a short incubation period, and some are asymptomatic or cause minor symptoms that cannot be recognized except in retrospect. With many viral infections, recovery occurs under the influence of the body's defenses, but some become latent. In latent infection, the viral RNA or DNA remains in the host cells without causing disease for a long time, sometimes for many years. Most often, infection from person to person occurs during the asymptomatic period with hidden, latent forms of viral infections. Various triggers can cause re-activation of the process, this especially often occurs during immunosuppression.

Common viruses that remain latent are:

• Herpes viruses.
• Papovaviruses.

Some diseases are caused by reactivation of the virus in the central nervous system after a very long period of latency. These diseases include progressive multifocal leukodystrophy (polyomavirus K), subacute sclerosing panencephalitis (measles virus), and progressive rubella panencephalitis (rubella virus). Spastic pseudosclerosis and bovine spongiform encephalopathy were previously classified as slow viral diseases due to long incubation periods (years), but are now known to be caused by prions; Prions are protein pathogens that are not bacteria, fungi or viruses and that do not contain genetic material.

Several hundred different viruses can infect people. Such viruses are often spread through respiratory and intestinal secretions. Some are transmitted through sexual contact and blood transfusions. Some viruses are transmitted by arthropod vectors. Viruses are distributed throughout the world, but their pathogenicity is limited by innate resistance, resistance, post-vaccination immunity, sanitary and other health system control methods, and prophylactic antiviral drugs.

Zoonotic viruses carry out their biological cycles mainly in animals; humans are secondary or accidental hosts. These viruses exist in a specific environment that is able to support their natural cycles that differ from humans (vertebrates, arthropods, or both).

Viruses and cancer. Some viruses are oncogenic and predispose to certain cancers:

• Papillomavirus: cervical and anal carcinoma.
• Human T-lymphotropic virus 1: certain types of human leukemia and lymphoma.
• Epstein-Barr virus: nasopharyngeal carcinoma, Burkitt's lymphoma, Hodgkin's lymphoma and lymphomas in organ transplant recipients and the immunocompromised.
• Hepatitis B and C viruses: hepatocellular carcinoma.
• Human herpesvirus 8: Kaposi's sarcoma, primary lymphomas and multicentric Castleman disease (lymphoproliferative disease).

Types of viral diseases

Classification of viral infections according to the organ system affected (eg, lung, GI, skin, liver, CNS, mucosal membranes) can be clinically useful, although certain viral diseases (eg, mumps) are difficult to classify.

Respiratory infections. The most common viral infections are probably acute respiratory infections. Respiratory infections are more likely to cause severe symptoms in infants, the elderly, and patients with lung or heart problems.

Gastrointestinal infections. The age group affected primarily depends on the virus:

• Rotavirus: children.
• Norovirus: older children and adults.
• Astrovirus: usually infants and young children.
• Adenovirus 40 and 41: infants.
• Pathogens similar to coronavirus: infants.

Localized epidemics may occur in children, especially during colder times of the year.

The main symptoms are vomiting and diarrhea.

Rotavirus vaccine, which is effective against most pathogenic strains, is part of the recommended childhood vaccination schedule. Hand washing and good sanitation can help prevent the spread.

Exanthematous infections. Some viruses cause only skin lesions (as with molluscum contagiosum and warts); others may cause systemic manifestations or skin lesions on various parts of the body. Transmission typically occurs from person to person; The carrier of alpha viruses is the mosquito.

Liver infections. At least 5 specific viruses (hepatitis viruses A, B, C, D and E) can cause hepatitis; each causes a specific type of hepatitis. The hepatitis D virus can only infect people if there is hepatitis B.

Other viruses can also attack the liver. Common examples are cytomegalovirus, Epstein-Barr virus, and yellow fever virus. Less common examples are echovirus, coxavirus, and the herpes simplex, measles, rubella, and varicella viruses.

Neurological infections. Most cases of encephalitis are caused by viruses. Many of these viruses infect humans through the bites of arthropods, mainly mosquitoes and blood-feeding ticks; these viruses are called arboviruses. For such infections, prevention includes avoiding sandfly (mosquito) and tick bites.

Hemorrhagic fever. Certain viruses cause fever and a tendency to bleed or bleed. Spread by mosquitoes, ticks, or contact with infected animals (eg, rodents, monkeys, bats) and people.

Infections of the skin or mucous membranes. Some viruses cause lesions of the skin or mucous membranes, which recur and can become chronic. Infections affecting the skin and mucous membranes are the most common type of herpes simplex viral infection. The human papillomavirus causes warts. Transmission by person-to-person contact.

Diseases with multiple lesions of various systems and organs. Enteroviruses, which include coxsackieviruses and echoviruses, can cause various multisystem syndromes, as can cytomegaloviruses.

Nonspecific febrile illness. Some viruses cause nonspecific symptoms, including fever, malaise, headaches, and myalgia. Transmission usually occurs through insects or arthropods.

Rift Valley fever rarely progresses to eye lesions, meningoencephalitis, or the hemorrhagic form (which has a 50% mortality rate).

Virus diagnostics

Some viral diseases can be diagnosed clinically by familiar symptoms and syndromes (eg, measles, rubella, roseola infantum, erythema infectiosum, and varicella) or epidemiologically during epidemic outbreaks (eg, influenza). A clear laboratory diagnosis is needed primarily when specific treatment may be helpful or when the pathogen may be a public health threat (eg, HIV). Typical hospital laboratories can test for individual viruses, but for relatively rare diseases (eg, rabies, Eastern equine encephalitis), materials must be sent to public health laboratories or the Centers for Disease Control and Prevention.

Serological testing in the acute and convalescent phases is sensitive and specific but slow; faster diagnosis can sometimes be made using culture methods, PCR, and sometimes histochemical methods using electron microscopy to detect viral antigens.

Treatment of viruses

Antiviral drugs. Progress in the use of antiviral drugs is rapid. Antiviral chemotherapy can be aimed at various phases of viral replication: interfere with the process of attachment of the virus particle to the membranes of the host cell or decapsulation of the nucleic acids of the virus, inhibit the cellular receptor or factor necessary for viral replication, block specific virus-encoded enzymes and proteins that are produced in host cells and which are important for viral replication rather than normal host cell metabolism.

Antivirals are most often used therapeutically or prophylactically against herpesviruses (including cytomegalovirus), respiratory viruses, and HIV. However, some drugs are effective against different types of viruses.

Interferons. Interferons are substances produced by infected host cells in response to viral or other foreign antigens. There are many different interferons that have numerous

effects such as blocking viral RNA translation and transcription and stopping viral replication without interfering with normal host cell function. Sometimes interferons are attached to polyethylene glycol (pegylated compounds), which gives a slow and prolonged release of interferon.

Viral diseases that can be treated with interferon:

• Chronic hepatitis B and C.
• Condyloma acuminata.
• Hairy cell leukemia.
• Kaposi's sarcoma.

Depression and, with large doses, bone marrow suppression are also possible.

Virus prevention

Vaccines. Vaccines work to stimulate the innate immune system. Vaccines used include hepatitis A, hepatitis B, human papillomavirus, influenza, measles, mumps, polio, rabies, rotavirus, rubella, chickenpox and yellow fever. adenovirus and smallpox vaccines are available but are used only in at-risk groups (eg, army recruits).

Immunoglobulins. Immunoglobulins are available for passive immunoprophylaxis in selected situations. They can be used when there is a risk of infection (for example, hepatitis A), after infection (for example, rabies or hepatitis) and to treat a disease (for example, eczema vaccinatum).

Preventive measures. Many viral infections can be prevented by common preventive measures (which vary depending on how the pathogen is transmitted). Hand washing, proper food preparation and water handling, avoiding contact with sick people and practicing safe sex are important. Regarding infections that are carried by insects (eg mosquitoes, ticks), it is important to protect yourself from contact with them.