The smallest pathogens of various infectious diseases are called viruses. They are intracellular parasites.
Virus spread
All the most famous infections on the planet are caused by these parasites. They are able to affect all living things, including the simplest microorganisms. Almost 80% of all infectious diseases that affect humans are caused by viruses. There are more than 10 main groups that are pathogenic to the body.
But viruses cannot be too dangerous for their host. Otherwise, this can lead to the complete disappearance of the donor organism, which means that the pathogen will also be destroyed. But viruses cannot be too weak. If immunity develops too quickly in the host’s body, then they will disappear as a species. It often happens that these microorganisms have one host inside which they live without causing the latter any troubles, while they also have a pathogenic effect on other living creatures.
They reproduce by reproduction. This means that their nucleic acids and proteins are first reproduced. And then viruses are compiled from the created components.
Types of virions and ways of infection
Before you understand how the multiplication of viruses in the cell, you need to understand how these particles get there. For example, there are infections that spread exclusively by humans. These include measles, herpes, and partly flu. They are transmitted by contact or by airborne droplets.
Enteroviruses, reoviruses, adenoviruses can enter the body through the diet. For example, papillomavirus can be infected by direct contact with a person (both household and sexual). But there are other ways of infection. For example, some types of rhabdoviruses can be infected by a bite of blood-sucking insects.
There is also a parenteral route of infection. For example, hepatitis B virus can enter the human body through surgical procedures, dental procedures, blood transfusions, pedicures or manicures.
Do not forget about the vertical route of transmission of infections. In this case, if the mother is ill during pregnancy, the fetus is affected.
Virus description
For a sufficiently long time, the causative agents of most diseases were judged only on the basis of the pathogenic effect on the body. Scientists only managed to see these pathogens when an electron microscope was invented. Then it was possible to find out how the reproduction of viruses is carried out.
These microorganisms vary markedly in size. Some of them are similar in size to small bacteria. The smallest are close in size to protein molecules. To measure them, use a conditional value - a nanometer, which is equal to one millionth of a millimeter. They can be from 20 to several hundred nanometers. In appearance, they are similar to sticks, balls, cubes, threads, polyhedrons.
The composition of microorganisms
To understand how the multiplication of viruses occurs in cells, you need to understand their composition. Simple pathogens are made up of nucleic acids and proteins. Moreover, the first component is a carrier of genetic data. They consist of only one type of nucleic acid - it can be DNA or RNA. This classification is the basis for their classification.
If viruses are components of a living system inside a cell, then outside of them they are inert nucleoproteins called virions. Their obligatory component are proteins. But in different types of viruses they differ. Due to this, they can be recognized using specific immunological reactions.
Scientists have discovered not only simple viruses, but also more complex organisms. They may also include lipids, carbohydrates. Each group of viruses has a unique composition of fats, proteins, carbohydrates, nucleic acids. Some even have enzymes.
The beginning of the breeding process
Viruses are considered absolute parasites. They cannot live if they do no harm. Their pathological effect is based on the fact that, multiplying, they kill the cell in which they are located.
To understand how this process occurs, you can, if we examine in detail how the microorganism penetrates the cell, and what happens after that. Virions can be imagined as a particle consisting of DNA (or RNA), enclosed in a protein cover. Virus reproduction begins only after the microorganism attaches to the cell wall, to its plasma membrane. It should be understood that each virion can attach only to certain types of cells in which there are special receptors. Hundreds of viral particles can be located on one cell.
After this, the process of viropexis begins. The cell itself draws in the attached virions. Only after this begins the "undressing" of viruses. With the help of the complex of enzymes entering the cell, the protein coat of the virus is dissolved and the nucleic acid is released. It is she who passes through the channels of the cell into her nucleus or remains in the cytoplasm. Acid is responsible not only for the reproduction of viruses, but also for their hereditary characteristics. Own metabolism in cells is suppressed, all forces are directed to create new components of viruses.
Composition process
The nucleic acid of the virus is embedded in the DNA of the cell. Inside, multiple copies of viral DNA (RNA) begin to be actively created, this is done with the help of polymerases. Some of the newly created particles bind to the ribosomes, and the synthesis of new virus proteins takes place there.
As soon as a sufficient number of virus components has been accumulated, the composition process will begin. It passes near the cell walls. Its essence lies in the fact that new virions are assembled from the components. This is how the virus propagates.
As part of the newly formed virions, one can detect particles of cells in which they were located. Often the process of their formation ends in the fact that they are enveloped in a cell membrane layer.
Breeding completion
As soon as the composition process ends, the viruses leave their first host. Formed offspring leaves and begins to infect new cells. Propagation of viruses occurs directly in the cells. But they eventually they are completely destroyed or partially damaged.
Having infected new cells, viruses begin to proliferate in them. The reproduction cycle is repeated. How the exit process of the created virions will go depends on the group of viruses to which they belong. For example, enteroviruses are characterized by the fact that they are rapidly released into the environment. But herpes agents, reoviruses, orthomyxoviruses emerge as they mature. Before dying, they can go through several cycles of such reproduction. At the same time, cell resources are depleted.
Diagnosis of diseases
The reproduction of bacteria and viruses in some cases is accompanied by the fact that particles of pathogenic microorganisms can accumulate inside the cells, forming crystalline clusters. Specialists call them inclusion bodies.
For example, with influenza, smallpox, or rabies, such clusters are in the cytoplasm of cells. With spring-summer encephalitis, they are found in the nucleus, and with other infections they can be both there and there. This symptom is used to diagnose diseases. In this case, it is also important where exactly the process of reproduction of viruses occurs.
For example, when oval or round formations are found in epithelial cells, they speak of smallpox. Cytoplasmic accumulations in brain cells indicate rabies.
The method of propagation of viruses is very specific. First, the virions enter the cells that suit them. After this, the process of releasing nucleic acids and creating “blanks” of parts for future pathogenic microorganisms begins. The process of reproduction ends with the completion of new virions that enter the environment. It is enough to disrupt one of the stages of the cycle so that the reproduction of viruses is stopped or they begin to give inferior offspring.