Viral diseases can be recognized by their characteristic signs. This does not require any complex devices, which are more often seen in pictures in textbooks than doctors in their offices.
The main distinguishing feature of viruses is as follows:any virus needs the help of other cells in the body to reproduce. Everything happens as follows.
There is a specific cell into which the virus enters. Precisely "definite", since viruses have the property of selectivity. They cannot settle in any cell that comes along, there should only be one that allows the virus to develop. This selected cell becomes infected, and quite definite signs of the disease appear. She further spreads this virus throughout the body.
For example, infectious hepatitis is viral. This virus lives and multiplies only in liver cells; nowhere else it can live. As well as mumps - in the salivary glands, influenza affects the mucous membranes of the bronchi and trachea, and encephalitis - only brain cells. Any virus infects its organ, its cells. Such selectivity is expressed not only in relation to a certain type of cells, but also to certain types of organisms. For example, measles can only be in humans, and it will not affect the body of pets. Canine plague spreads only among dogs; it is not dangerous for humans. But there are exceptions to this rule. The most common of these is rabies.
Each cell of a living organism performs quite specific functions that are unique to it. The defeat of this cell by a virus causes problems in its work. The virus in the liver leads to liver failure, in the lungs and bronchi it is expressed by cough and hoarseness, and brain damage leads to disturbances of consciousness and paralysis. That is, the symptoms of damage to one or another organ are very specific. But in any case, these cells no longer fulfill their purpose.
Viral infection varies in severity. It all depends on the number of cells affected, as well as on which cells are infected. It is clear that brain damage is more dangerous than the mucous membranes of the lungs. There are two more important points that relate to the severity of the disease. The cells of the body grow and develop over time. That is, they are different in a child and an adult. And in children's cells, most viruses simply cannot develop. Take, for example, hepatitis A. This virus does not infect children under one year old. It is easily tolerated by older children. But in adulthood, people get very seriously ill, especially "childhood" diseases such as measles and chickenpox. The severity of the course of the disease still depends to a greater extent on the initial health of the cell. Bad habits have a very strong effect on health.
The initial reaction of the body to the penetration of a virus into it is to fight it. Subsequently, antibodies appear that protect the body by neutralizing viruses. This leads to a quick end to the disease. Everything seems to be simple here. But this is far from the case. There are times when antibodies cannot be produced quickly, and the virus “captures” more and more new cells. During this time, he manages to take root and infect the organ, which leads to dire consequences. In another case, the virus, on the contrary, "stops" by infecting some cells. It turns out that the body is infected, but the disease has no continuation. As a rule, he begins to show himself only when immunity weakens.
An actively multiplying virus is very dangerous. It destroys the cell in which it sits, getting further directly into the blood. There antibodies begin to fight it. This leads to the emergence of infectious diseases. Their duration depends on how long the body needs to create these antibodies. In general, infectious diseases last no more than ten days. This allows the doctor to determine the time of illness with great accuracy. It can also be concluded that infections cannot last longer than this period, otherwise they are no longer infections.
The main difficulty in the treatment of infectious diseases is the fact that cell infection occurs. It is very difficult to eliminate the disease, to destroy the virus, while keeping the cell in a normal, healthy state. There are very few drugs that help in this fight. In addition, each drug is targeted to a specific type of virus. The basic principle in the treatment of diseases caused by viral infections- to allow the body to defeat the disease on its own To do this, he needs help.
What can it be?
To fight, it is necessary to create conditions that include the following components:
- daily regime;
- diet food;
- medicine.
The essence of the treatment is as follows:Dealing with symptoms. Treat rashes, soften coughs, relieve nasal congestion, lower fever. Taking medications that will improve the functions of an organ, or simply, if possible, reduce the load on infected organs.
In the fight against viruses, the main place should be occupied by the prevention of diseases. It includes:
- Vaccination.
- In essence, weakened strains of viruses are introduced that promote the production of antibodies.
- Limiting contacts with carriers of the virus.
- A lifestyle is important, which contributes to the formation of good immunity.
American scientists have published data from recent studies, in which they noted a downward trend in puberty in American adolescents. Comparing the results of recent studies and data from ten years ago, scientists note that this is not so ...
1 INTRODUCTION PAGE 1
2. EVOLUTIONARY ORIGIN PAGE 2
3. PROPERTIES OF VIRUSES. THE NATURE OF VIRUSES. PAGE 2
4. STRUCTURE AND CLASSIFICATION OF VIRUSES PAGE 3
5. INTERACTION OF VIRUS WITH CELLS PAGE 6
6. SIGNIFICANCE OF VIRUSES PAGE 7
7. VIRAL DISEASES PAGE 9
8. SPECIFIC FEATURES OF VIRUS EVOLUTION ON SOREMEN
STAGE. PAGE 14
9. CONCLUSION. PAGE 15
10. LIST OF USED LITERATURE. PAGE 16
Introduction
By the end of the last century, no one doubted that every infectious disease is caused by its own microbe, which can be successfully fought.
"Give only a time limit," said the bacteriological scientists, "and soon there will be no disease left." But years passed and promises were not kept. People were infected with measles, foot and mouth disease, polio, trachoma, smallpox, yellow fever, and influenza. Millions of people died from terrible diseases, but microbes - pathogens were not found.
Finally, in 1892. the Russian scientist D.I.Ivanovskiy attacked the right track. Studying tobacco mosaic - a disease of tobacco leaves, he came to the conclusion that it is not caused by a microbe, but something smaller. This “something” penetrates through the thinnest filters capable of retaining bacteria, does not multiply in artificial environments, perishes when heated, and could not be seen through a light microscope. Filterable poison!
This was the conclusion of the scientist. But poison is a substance, and the causative agent of tobacco disease was a creature. It reproduced well in plant leaves. Danish botanist Martin Willem Beirinik called this new "something" a virus, adding that the virus is "a liquid, living, contagious, beginning." In translation from Latin "virus" means "poison"
A few years later, F. Leffler and P. Frosch discovered that the causative agent of foot and mouth disease, a disease often found in livestock, also passes through bacterial filters. Finally, in 1917, the Canadian bacteriologist F. de Erelle discovered a bacteriophage, a virus that infects bacteria.
This is how viruses of plants, animals and microorganisms were discovered. These events marked the beginning of a new science - virology studying non-cellular life forms.
Evolutionary origin of viruses
The nature of viruses is still causing heated discussions among specialists. The reason for this is in many respects the numerous and often very contradictory hypotheses expressed to date and, unfortunately, objectively not proven by anything.
More plausible, it seems hypothesis about the endogenous origin of viruses ... According to her, viruses are a fragment of a once cellular nucleic acid that has adapted to separative replication. This version is to some extent confirmed by the existence of plasmids in bacterial cells, the behavior of which is in many ways similar to viruses. Along with this, there is a "cosmic" hypothesis, according to which viruses did not evolve on Earth at all, but were brought to us from the Universe by means of some cosmic bodies.
Properties of viruses. The nature of viruses
2. They do not have their own metabolism, they have a very limited number of enzymes. For reproduction, the metabolism of the host cell, its enzymes and energy are used.
Viruses do not multiply on artificial culture media - they are too picky about food. Regular broth, which most bacteria suit, is not good for viruses. ... They need living cells , and not any, but strictly defined. Like other organisms, viruses are capable of reproduction. Viruses possess heredity. ... The hereditary traits of viruses can be taken into account by the spectrum of the affected hosts and the symptoms of the diseases caused, as well as by the specificity of the immune responses of natural hosts or artificial immunized experimental animals. The sum of these features makes it possible to clearly determine the hereditary properties of any virus, and even more - its varieties that have clear genetic markers, for example: the neurotropicity of some influenza viruses, etc. ... Variability is the other side of heredity , and in this respect, viruses are similar to all other organisms that inhabit our planet. At the same time, in viruses one can observe both genetic variability associated with a change in the hereditary substance, and phenotypic variability associated with the manifestation of the same genotype under different conditions.
The structure and classification of viruses
Viruses cannot be seen with an optical microscope because they are smaller than the wavelength of light. They can only be seen with the help of an electron microscope.
Viruses are composed of the following main components :
1 ... The core is the genetic material (DNA or RNA) that carries information about several types of proteins needed to form a new virus.
2 ... Protein shell, which is called capsid (from the Latin word caps - box). It is often built from identical repeating subunits called capsomeres. Capsomeres form structures with a high degree of symmetry.
3 ... Additional lipoprotein membrane. It is formed from the plasma membrane of the host cell and is found only in relatively large viruses (influenza, herpes).
The capsids and the additional envelope carry protective functions, as if protecting the nucleic acid. In addition, they facilitate the entry of the virus into the cell. A fully formed virus is called a virion.
The schematic structure of an RNA-containing virus with a spiral type of symmetry and an additional lipoprotein envelope is shown on the left in Figure 2, on the right its enlarged cross section is shown.
Figure: 2. Schematic structure of the virus: 1 - core (single-stranded RNA); 2 - protein shell (Capsid); 3 - additional lipoprotein membrane; 4 - Capsomeres (structural parts of the Capsid).
The number of capsomeres and the way they are packed are strictly constant for each type of virus. For example, the poliomyelitis virus contains 32 capsomeres, while the adenovirus contains 252.
Since the basis of all living things is made up of genetic structures, then viruses are now classified according to the characteristics of their hereditary substance - nucleic acids. All viruses are divided into two large groups : DNA viruses (deoxyviruses) and RNA viruses (riboviruses). Each of these groups is then subdivided into double-stranded and single-stranded nucleic acid viruses. The next criterion is the type of symmetry of virions (depending on the method of packing the capsomeres), the presence or absence of outer membranes, according to the cells - the hosts. In addition to these classifications, there are many others. For example, by the type of transmission of infection from one organism to another.
|
|
|
|
Figure: 3. Schematic representation of the location of capsomeres in the capsid of viruses. The spiral type of symmetry has the influenza virus - a ... Cubic type of symmetry in viruses: herpes - b , adenovirus - in , poliomyelitis - r
COATING Double-stranded The genetic material of the virus (DNA or RNA) is surrounded by a protein coat. DNA structure of viruses
smallpox viruses
herpes - viruses
Single-stranded RNA
measles viruses, mumps
rabies viruses
viruses of leukemia, AIDS
UNBELLLESS
Double-stranded DNA
irido - viruses
adeno - viruses
Interaction of a virus with a cell
Viruses can live and reproduce only in the cells of other organisms. Outside the cells of organisms, they show no signs of life. In this regard, viruses are either an extracellular resting form (varion),
or intracellular replicating - vegetative. Varions show excellent vitality. In particular, they can withstand pressures up to 6000 atm and tolerate high doses of radiation, but they die at high temperatures, exposure to UV rays, as well as exposure to acids and disinfectants.
Interaction of a virus with a cell several stages pass sequentially:
1. First stage represents adsorption of varions on the surface of the target cell, which for this must have the appropriate surface receptors. It is with them that a viral particle specifically interacts, after which their strong binding occurs, for this reason, cells are not susceptible to all viruses. This explains the strict certainty of the pathways of entry of viruses. For example, receptors for the influenza virus are found in mucosal cells respiratory tract, but skin cells do not. Therefore, you cannot get the flu through the skin - viral particles must be inhaled with air, the hepatitis A or B virus penetrates and multiplies only in the liver cells, and the mumps virus (mumps) - in the cells of the parotid salivary glands, etc.
2. Stage two consists of penetration the whole varion or its nucleic acid inside the host cell.
3.Third stage called deproteinization ... In the course of it, the carrier of the genetic information of the virus - its nucleic acid - is released.
4. During fourth stage based on viral nucleic acid occurs synthesis of compounds necessary for the virus.
5.In fifth stage happens synthesis of viral particle components - nucleic acid and capsid proteins, and all components are synthesized many times.
6. During sixth stage from previously synthesized multiple copies of nucleic acid and proteins new virions are formed by self-assembly
7.Last - seventh stage - represents the release of newly collected viral particles from the host cell. This process is not the same for different viruses. In some viruses, this is accompanied by cell death due to the release of lytic enzymes from lysosomes - cell lysis. In others, varions leave a living cell by budding, however, in this case, the cell dies over time.
The time elapsed from the moment the virus enters the cell until the release of new varions is called latent or latency period. It can vary widely: from several hours (5-6 for smallpox and influenza viruses) to several days (measles viruses, adenoviruses, etc.
Another way of penetration into the cell for bacteria viruses is bacteriophages ... Thick cell walls do not allow the receptor protein, together with the attached virus, to submerge into the cytoplasm, as happens when animal cells are infected. Therefore, the bacteriophage introduces a hollow the rod into the cell and pushes through it the DNA (or RNA) that is in it head. The bacteriophage genome enters the cytoplasm, while the capsid remains outside. Into the cytoplasm bacterial the cell begins to replicate the bacteriophage genome, synthesize its proteins and form a capsid. After a certain period of time, the bacterial cell dies and mature phage particles are released into the environment.
Bacteriophages that form a new generation of phage particles in infected cells, which leads to the lysis (destruction) of a bacterial cell, are called virulent phages .
Some bacteriophages do not replicate inside the host cell. Instead, their nucleic acid is incorporated into the host's DNA to form a single molecule capable of replication. Such phages were named temperate phages , or prophages. The prophage has no lytic effect on the host cell and, during division, replicates together with cellular DNA. The bacteria containing the prophage are called lysogenic. They show resistance to the phage contained in them, as well as to other phages close to it. The connection of a prophage with a bacterium is very strong, but it can be broken under the influence of inducing factors (UV rays, ionizing radiation, chemical mutagens). It should be noted that lysigenic bacteria can change properties (for example, release new toxins).
The importance of viruses
Viruses of bacteria, plants, insects, animals and humans are known to science. There are more than 1000 of them. The processes associated with the multiplication of the virus most often, but not always, damage and destroy the host cell. The multiplication of viruses, coupled with the destruction of cells, leads to the occurrence of painful conditions in the body. Viruses cause many human diseases: measles, mumps, flu, poliomyelitis, rabies, smallpox, yellow fever, trachoma, encephalitis, some oncological (tumor) diseases, AIDS. It is not uncommon for people to develop warts. Everyone knows how after a cold they often "sweep" the lips and wings of the nose. These are also all viral diseases. Scientists have found that many viruses live in the human body, but they do not always manifest themselves. Only a weakened organism is exposed to the effects of a pathogenic virus. The ways of infection with viruses are very different: through the skin with insect and tick bites; through saliva, mucus and other discharge of the patient; through the air; with food; sexually and others. Drip infection is the most common way of spread respiratory diseases... When coughing and sneezing, millions of tiny droplets of liquid (mucus and saliva) are thrown into the air, which, along with the living microorganisms in them, can be inhaled by other people, especially in crowded places. In animals, viruses cause foot and mouth disease, plague, rabies; in insects - polyhedrosis, granulomatosis; in plants - mosaic or other changes in the color of leaves or flowers, curly leaves and other changes in shape, dwarfism; finally, bacteria have their decay. The concept of viruses as stopping at nothing "destroyers" persisted in the study of a special group of viruses that infect bacteria. We are talking about bacteriophages. The ability of phages to kill bacteria can be used to treat some diseases caused by these bacteria. Phages were indeed the first group of viruses "tamed" by humans. They quickly and mercilessly dealt with their closest neighbors in the microworld. Sticks of plague, typhoid fever, dysentery, cholera vibrios literally "melted" before our eyes after meeting these viruses. They began to be used to prevent and treat many infectious diseases, but, unfortunately, the first successes were followed by failures. This was due to the fact that phages attacked bacteria in the human body not as actively as in a test tube. In addition, bacteria turned out to be "more cunning" than their enemies: they very quickly adapted to phages and became insensitive to their action.
After the discovery of antibiotics, phages as a medicine receded into the background, but they are still successfully used to recognize bacteria. The fact is that phages are able to very accurately find "their bacteria" and quickly dissolve them. Similar properties of phages formed the basis of medical diagnostics. This is usually done as follows: the bacteria isolated from the patient's body are grown on a solid nutrient medium, after which various phages are applied to the resulting "lawn", for example, dysentery, typhoid, cholera and others. After a day, the dishes are viewed in the light and determine which phage caused the bacteria to dissolve. If a dysentery phage had such an effect, then dysentery bacteria were isolated from the patient's body, if typhoid - typhoid bacteria.
Sometimes viruses that infect animals and insects come to the aid of a person. More than twenty years ago, the problem of fighting wild rabbits arose in Australia. The number of these rodents has reached alarming proportions. They destroyed crops faster than locusts and became a real national disaster. Conventional methods of dealing with them have proven ineffective. And then scientists released a special virus to fight rabbits, capable of destroying almost all infected animals. But how to spread this disease among shy and wary rabbits? Mosquitoes helped. They played the role of "flying needles", carrying the virus from rabbit to rabbit. At the same time, the mosquitoes remained completely healthy.
There are other examples of the successful use of viruses to kill pests. Everyone knows the damage caused by caterpillars and sawfly beetles. The former eat the leaves of useful plants, the latter infect trees in gardens and forests. The so-called polyhedrosis and granulose viruses fight them, which are sprayed with spray guns in small areas, and planes are used to treat large areas. This was done in the USA (California) when fighting caterpillars that infect alfalfa fields, and in Canada when destroying a pine sawfly. The use of viruses to combat caterpillars infecting cabbage and beets, as well as to destroy domestic moths, is also promising.
What happens to a cell if it is infected with not one, but two viruses? If you decided that in this case the cell's disease would worsen and its death would accelerate, then you were wrong. It turns out that the presence of one virus in a cell often reliably protects it from the destructive effect of another. This phenomenon has been named by scientists as virus interference. It is associated with the production of a special protein - interferon, which activates a protective mechanism in cells that can distinguish viral from non-viral and selectively suppress viral. Interferon inhibits the multiplication in cells of most viruses (if not all). Interferon, which is produced as a therapeutic drug, is now used to treat and prevent many viral diseases.
What other useful things can you expect from viruses in the future? Let's jump into the realm of speculation. First of all, it is worth recalling genetic engineering. Viruses can be invaluable to scientists by capturing the desired genes in some cells and transferring them to others. Finally, there is another possibility of using viruses. Scientists have discovered a virion that can selectively destroy some tumors in mice. Viruses that kill tumor cells human. If it is possible to deprive these viruses of their pathogenic properties and at the same time preserve their property of selectively destroying malignant tumors, then in the future, it is possible that a powerful tool will be obtained to combat these serious diseases. The search for such viruses is underway, and now this work no longer seems fantastic and hopeless.
Let's briefly dwell on some viral diseases:
Smallpox
Smallpox - one of the oldest diseases. In the past, it was the most common and most dangerous disease... A description of smallpox was found in the Egyptian papyrus of Amenophis Ι, compiled 4000 years before our era. Smallpox lesions survived on the skin of a mummy buried in Egypt 3,000 BC. In the 16th and 18th centuries in Western Europe, in some years, up to 12 million people fell ill with smallpox, of which up to 1.5 million died. Its devastating power was as powerful as the plague. The problem of smallpox protection was solved only at the end of the 18th century by the English rural doctor Edward Jenner. Jenner was the first to prove that vaccination can suppress the spread of infectious diseases and expel them from the face of the Earth. The first mention of smallpox in Russia dates back to the 5th century. In 1610, the infection was brought to Siberia, where a third of the local population died out. People fled to the forests of the tundra and the mountains set up idols, burned scars like pockmarks on their faces in order to deceive this evil spirit - everything was in vain, nothing could stop the ruthless killer. Smallpox is an acute infectious disease characterized by general intoxication, fever and a rash on the skin and mucous membranes. Smallpox belongs to quarantine infections. The source of infection is a sick person, starting from the first days of the disease and until the crusts completely disappear. The transmission of the pathogen occurs mainly by airborne droplets, however, infection is also possible by airborne dust. Smallpox was widespread in Asia, Africa, South America. Smallpox was eliminated in the USSR in 1937. Smallpox has now been eradicated all over the world.
FLU
Influenza, in our opinion, is not such a serious disease, but it remains the "king" of epidemics. None of the diseases known today can cover hundreds of millions of people in a short time, and more than 2.5 billion people fell ill with influenza in just one pandemic (general epidemic).
Since the end of the nineteenth century. humanity has experienced four severe influenza pandemics: in 1889-1890, 1918-1920, 1957-1959 and 1968-1969. Pandemic 1918-1920 ("Spanish woman") carried away 20 million lives . Never before has influenza caused such a high mortality rate. 1957-1959. ("Asian flu") killed about 1 million people.
Several varieties of the influenza virus are known - A, B, C, and others; The inside of the influenza virus - the nucleotide (or core) contains a single-stranded RNA enclosed in a protein sheath. This is the most stable part of the virion, as it is the same for all influenza viruses of the same type. Type A influenza is the culprit in pandemics. Influenza B is less common and causes more limited epidemics; influenza C is even rarer.
Due to the fact that the immunity in influenza is short-term and specific, it is possible to get sick repeatedly in one season. According to statistics, an average of 20-35% of the population suffer from influenza every year.
The source of infection is a sick person; patients with a mild form as distributors of the virus are the most dangerous, since they do not isolate themselves in a timely manner - they go to work, use public transport, visit spectacular places. The infection is transmitted from sick person to healthy person by airborne droplets when talking, sneezing, coughing, or through household items.
Avian influenza in humans:
Influenza A viruses can infect not only humans, but also some species of animals and birds, including chickens, ducks, pigs, horses, ferrets, seals and whales. Influenza viruses that infect birds are called "bird (chicken) influenza" viruses. All species of birds can get sick with avian flu, although some species are less susceptible than others. Avian influenza does not cause epidemics in wild birds and is asymptomatic in them, but among poultry it can cause serious illness and death.
Avian influenza viruses, as a rule, do not infect humans, but there are cases of illness and even death among people during outbreaks of 1997- 
1999 and 2003-2004. In this case, a person is most likely the final link in the transmission of the influenza virus (you can get sick by contact with a live infected bird or by eating raw infected meat), because there are still no cases of reliable human-to-human transmission of this virus.
So in 1997 in Hong Kong the avian influenza virus (H5N1) was isolated, which infected both chickens and humans. This was the first time the avian influenza virus was found to be directly transmitted from birds to humans. During this outbreak, 18 people were hospitalized and 6 of them died. Scientists have determined that the virus spread directly from birds to humans.
Since the end of 2003, in the course of the avian flu epidemic that gripped Southeast and East Asia, the disease has killed 66 people, mostly in close contact with infected animals.
In the same year 2003, avian influenza viruses (H7N7) and (H5N1) were detected in the Netherlands in 86 people caring for infected poultry. The disease was asymptomatic or mild. Most often, the manifestations of the disease were limited to an eye infection with some signs of respiratory disease.
Avian influenza was recently discovered in Russia and Kazakhstan. However, not a single case of defeat dangerous virus people in these countries have not yet been recorded
Bird flu symptoms in humans:
Human bird flu symptoms range from typical flu-like symptoms (very heatdifficulty breathing, coughing, sore throat and muscle pain) to an eye infection (conjunctivitis). Such a virus is dangerous in that it can very quickly lead to pneumonia, and, in addition, it can give serious complications to the heart and kidneys.
2004 is the most common outbreak of avian influenza (H5N1) in humans. The main distinguishing features of the 2004 influenza virus can be summarized as follows:
- The virus has become more contagious, indicating a mutation in the virus.
The virus has overcome the interspecies barrier from birds to humans, but there is no evidence yet that the virus is transmitted directly from person to person (all sick people had direct contact with infected birds).
- The virus primarily infects and kills children.
- The source of infection and the route of spread of the virus have not been determined, which makes the situation with the spread of the virus practically uncontrollable.
- Prevention measures - complete elimination of all poultry.
Treatments for avian influenza in humans:
Research conducted so far confirms that prescribing drugs developed for human influenza strains will also work in the event of human avian influenza infection, but it is possible that influenza strains may become resistant to such drugs and become ineffective. ... The isolated virus was found to be sensitive to amantadine and rimantadine, which inhibit the reproduction of influenza A virus and are used in the therapy of human influenza.
What is the reason for the close attention to bird flu these days:All influenza viruses have the ability to change. The possibility exists that in the future, the avian influenza virus could change in such a way that it can infect humans and spread easily from person to person. Since these viruses do not usually infect humans, there is very little or no immune defense against such viruses in the human population. Should the avian flu virus become capable of infecting humans, an influenza pandemic could begin. Experts from the World Health Organization (WHO) believe that an avian flu pandemic could kill 150 million people on Earth. This fact is confirmed by American and British scientists: the results of their studies indicate that the Spanish flu (1918) was so deadly due to the fact that it evolved from bird flu and contained a unique protein to which humans had no immunity. Currently, there is a hypothesis about the emergence of a pandemic influenza virus through the transfer of genes from the reservoir of waterfowl to humans through pigs. |
In addition, the avian influenza virus, unlike human, is very stable in the external environment - even in the carcasses of dead birds, it can live up to one year, which increases the risk.
AIDS - Acquired immune deficiency syndrome is a new infectious disease, which experts recognize as the first truly global epidemic in the known history of mankind. Neither plague, nor smallpox, nor cholera are precedents, since AIDS is decidedly unlike any of these and other known human diseases. The plague claimed tens of thousands of lives in regions where the epidemic broke out, but never covered the entire planet at once. In addition, some people, having recovered from illness, survived, acquiring immunity and took on the work of caring for the sick and restoring the affected economy. AIDS is not a rare disease that few people can accidentally suffer from. Leading experts now define AIDS as a "global health crisis", as the first truly earthly and unprecedented epidemic infectious disease, which until now after the first decade of the epidemic is not controlled by medicine and every infected person dies from it.
By 1991, AIDS was registered in all countries of the world, except Albania. In the most developed country in the world - the United States, already at that time, one out of every 100-200 people was infected, another resident of the United States became infected every 13 seconds, and by the end of 1991 AIDS in this country became the third most fatal country, overtaking cancer. Now in the number of people infected with the virus, countries in Africa south of the Sahara are in the lead. A whole country in Africa - Zimbabwe can die out as a result of AIDS: every day here from this disease up to 300 people die! Among the adult population of large cities in Botsvana, the incidence reaches 30%. One in ten babies is already infected with the HIV virus. So far, AIDS is forced to admit that it is a fatal disease in 100% of cases.
The first people with AIDS were identified in 1981, and in 1983. managed to prove that it is caused by a previously unknown human virus from the family of retroviruses. This virus contains only its inherent enzyme - reverse transcriptase (RNA - dependent DNA pomerase), which is a part of only these viruses. Its discovery was a real revolution in biology, as it showed the possibility transmission of genetic information not only according to the classical DNA - RNA - protein scheme, but also by reverse transcription from RNA to DNA ... This is how a “false program” (provirus) appears in the cell, which changes the genome much more strongly than is possible with “normal” evolutionary variability.
In the human body retrovirus HIV infects only certain cells - the so-called T4 lymphocytes by binding to a special membrane protein. Unfortunately, it is these cells that play the main role in immune system management ... Inserting itself, the virus introduces its RNA, on the matrix of which the provirus DNA is synthesized, in order to then integrate into the genome of the host cell. In this capacity, HIV can be present in the body for up to ten years, without manifesting itself in any way.
But if, under the influence of some other infections, lymphocytes are activated, the built-in area "wakes up" and begins to actively synthesize HIV particles. Then viruses destroy the membrane and kill lymphocytes, which leads to the destruction of immunity, as a result of which the body loses its protective properties and is unable to withstand pathogens of various infections and kill tumor cells. The insidiousness of HIV in it unusually high mutation capacity - which makes it impossible to create an effective vaccine and universal medicine.
How does infection occur ? The source of infection is a person infected with the immunodeficiency virus. This can be a patient with various manifestations of the disease, or a person who is a carrier of the virus, but does not have signs of the disease (asymptomatic virus carrier).
Ways of transmission of infection: sexual,
AIDS is transmitted only from person to person:
1.sexually (horizontal path)
2.parenteral, when a viral agent is introduced directly into the blood of a susceptible organism (transfusion of blood or blood products), organ transplantation or intravenous administration of drugs (drugs) with shared syringes or needles, performing ritual rituals associated with bloodletting, cuts with an HIV-infected instrument.
3.from mother to fetus and newborn (vertical path).
The risk groups for AIDS infection are homosexual men, "intravenous" drug addicts, prostitutes, people with a large number of sexual partners, frequent donors, hemophilia patients, children born to HIV-infected people.
Prevention measures ... The main condition is your behavior!
Features of the evolution of viruses at the present stage.
The evolution of viruses in the era of scientific and technological progress as a result of powerful pressure of factors is proceeding much faster than before. As examples of such intensively developing processes in the modern world, one can point to the pollution of the external environment with industrial waste, the widespread use of pesticides, antibiotics, vaccines and other biological products, a huge concentration of the population in cities, the development of modern vehicle, economic development of previously unused territories, the creation of industrial animal husbandry with the largest in terms of number and population density of animal farms. All this leads to the emergence of previously unknown pathogens, changes in the properties and circulation pathways of previously known viruses, as well as to significant changes in the susceptibility and resistance of human populations.
Impact of environmental pollution.
The modern stage of development of society is associated with intense pollution of the external environment. With certain indicators of air pollution, some chemicals and dust from production wastes, there is a noticeable change in the resistance of the body as a whole and, first of all, of the cells and tissues of the respiratory tract. There is evidence that under these conditions, some respiratory viral infections, such as influenza, are much more severe.
The consequences of the massive use of pesticides.
This may lead to the emergence of clones and populations of viruses with new properties and, as a result, new unexplored epidemics.
Conclusion
The fight against viral infections is fraught with numerous difficulties, among which the immunity of viruses to antibiotics should be noted. Viruses are actively mutating, and new strains regularly appear, against which a "weapon" has not yet been found. First of all, this applies to RNA-containing viruses, the genome of which is usually larger and, therefore, less stable. To date, the fight against many viral infections is developing in favor of humans, mainly due to the universal vaccination of the population for preventive purposes. Such events ultimately led to the fact that by now, according to experts, the variola virus has disappeared in nature. As a result of general vaccination in our country, in 1961. epidemic poliomyelitis has been eradicated. However, nature is still testing a person, from time to time, presenting surprises in the form of new viruses that cause terrible diseases. The most striking example is the human immunodeficiency virus, the fight against which a person is still losing. Its spread is already in line with the pandemic.
Bibliography:
1.H. Green. W. Stout. D. Taylor. "Biology" in 3 volumes, volume 1. Translation from English. Edited by R. Soper. Mir Publishing House. Moscow, 1996
2. E.P. Shuvalov "Infectious Diseases", 1990
3. G.L.Bilich "Biology full course", 2005
4.N.B. Chebyshev Biology, 2005
5. Golubev D.B., Soloukhin V.Z. "Reflections and controversies about viruses". Moscow, publishing house "Young Guard", 1989.
7. Zhdanov V.M., Gaidamovich S.Ya. "General and private virology". M .: "Medicine", 1982.
8. Golubev D.B., Soloukhin V.Z. "Reflections and controversies about viruses." M .: "Young Guard", 1982.
3. Zhdanov V.M., Ershov F.I., Novokhatsky A.S. "Secrets of the Third Kingdom". Moscow, ", 1971.
5. Zuev V.A. "The third face". Moscow, publishing house "Knowledge", 1985.
11. Cherkes F.K., Bogoyavlenskaya L.B., Belskaya N.A. "Microbiology". Moscow, publishing house "Medicine", 1987.
12. Chumakov M.P., Lvov D.K. "Questions of Virology". Moscow, publishing house of the USSR Academy of Medical Sciences, 1964.
13. A selection of articles under the general title "December 1 - World AIDS Day". Monthly popular science magazine "Health" No. 12 (513) 1997, pp. 38-41.
An interesting article about the role of viruses in the evolution of mankind. For an individual person infected with a virus, this virus is, of course, a great evil. But for humanity as a whole, everything is far from so simple.
We often have to deal with various diseases that are associated with viral infections. We hear that viruses can be biological weapons, and hundreds of thousands of people die from them. Yes, the AIDS virus has caused a pandemic across the planet, and the Ebola virus can kill entire villages in Africa. But ... There are scientists who claim that viruses are one of the important factors in evolution. How could it happen that one of the enemies of mankind helped him to become the head of nature? Let's start with how viruses live in human cells and what they need from us.
Viruses infect not only animals but also plants, fungi, bacteria, and even other viruses. It is assumed that at some stage of evolution, these agents separated from cell forms and continued to evolve in parallel. What is the purpose of the virus infecting a cell? Let's start with the fact that no virus can multiply outside the host cell, this is non-cellular form life, which contains only DNA / RNA and some proteins that protect genetic information and are necessary for the first stages of cell infection. Once in a cell, the virus needs to multiply as efficiently as possible, using cellular enzymes, which in most cases disrupts its work.
In addition, very often the viral particles that are formed in the cell can kill it during the release into the intercellular space. But it is not very profitable to kill your house. Therefore, most viruses have their own host, such as, for example, the human herpes virus, which affects the human race for a long time. Such viruses have adapted to their hosts and do not bring them significant harm. Therefore, approximately 95% of the world's population has the human herpes virus, but this does not threaten us with extinction.
Moreover, some scientists assert that if we got rid of our "usual" viruses, then, perhaps, their place would be taken by new, more aggressive pathogens. This is the first factor in the joint evolution of viruses and cellular forms (including humans), which is carried out approximately according to the following scheme. The new virus infects, for example, the human population, those from the population that cannot cope with this virus die or get sick. And those who can somehow fight this disease continue to live and give birth to the same persistent children, that is, they transmit their genetic information. In turn, the virus can also mutate. That is, those strains that were aggressive and killed their owners do not have the ability to reproduce, and those that are less aggressive allow their owners to live and, as a result, successfully reproduce, as those that others.
That is why those viruses are especially dangerous for us, the owners of which we are not, for example, animal viruses (cases of human infection with a plant or bacterial virus are not yet known). The same HIV "migrated" to us from monkeys who are resistant to it and do not get sick with any AIDS-related diseases. Scientists suggest that by 2300 HIV will not be as deadly for humans as the human herpes virus. But if we talk about evolution, then this is not the only point.
Depending on how the virus encodes the genetic information and life cycle, they can multiply in very different ways. One of the most interesting ways is the propagation of retroviruses. These are RNA-containing viruses that, once in the cell, synthesize DNA from this RNA, this DNA is integrated into the host's genome, and from it, along with useful proteins, the cell synthesizes viral proteins. A cell does not know which DNA is it, and which is the virus, since this DNA is in my genome, then it is worth doing what is written on it. And if such a virus is embedded in the germ cells, then it will be very easily transmitted in a vertical way, that is, from parent to child. And the child will pick up a couple more of these viruses and pass them on to their children, and so on.
Over time, the immune system will react to some viruses and learn how to fight them, and the viral DNA that deactivates in the genome, but perhaps that DNA contains some sequences that were not previously in the cell, and they can greatly facilitate its life , then the "smart" cell will not deactivate them. It is estimated that 5-8% of the human genome contains retroviruses. Yes, maybe this is a "time bomb", as some scientists say, and one day these retroviruses may "come to life", but maybe this is the reason that we are who we are. Nature is not stupid, she will not do anything to her detriment. So it's worth fighting new epidemics, but don't be too afraid of them, because there are two ways: either development or degradation, there is no other way.