The smallest pathogens of various infectious diseases are called viruses. They are intracellular parasites.
Spread of viruses
All the most famous infections on the planet are caused by these parasites. They are able to infect 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 major groups that are pathogenic to the body.
But viruses can't 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 either. If immunity develops too quickly in the host organism, they will disappear as a species. It often happens that these microorganisms have one host, inside which they live, without causing trouble to the latter, and at the same time they have a pathogenic effect on other living beings.
They reproduce by reproduction. It means,that their nucleic acids and proteins are reproduced first. And then viruses are assembled from the created components.
Types of virions and routes of infection
Before you understand how viruses reproduce in a cell, you need to understand how these particles get there. For example, there are infections that are spread exclusively by humans. These include measles, herpes, and part of the flu. They are transmitted by contact or airborne droplets.
Enteroviruses, reoviruses, adenoviruses can enter the body through food. For example, you can become infected with papillomavirus through direct contact with a person (both domestic and sexual). But there are other routes of infection. For example, some types of rhabdoviruses can be transmitted through the bite of blood-sucking insects.
There is also a parenteral route of infection. For example, the hepatitis B virus can enter the human body through surgery, dental procedures, blood transfusions, pedicures, or manicures.
Do not forget about the vertical transmission of infections. In this case, when the mother falls ill during pregnancy, the fetus is affected.
Description of viruses
For quite a long time, the causative agents of most diseases were judged only on the basis of a pathogenic effect on the body. Scientists only managed to see these pathogenic organisms when the electron microscope was invented. At the same time, it was possible to find out how viruses reproduce.
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, a conditional value is used - 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.
Composition of microorganisms
To understand how viruses reproduce in cells, you need to understand their composition. Simple pathogens are composed of nucleic acid 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. Their classification is based on this difference.
If inside the cell viruses are components of a living system, outside of them they are inert nucleoproteins called virions. Proteins are their essential component. But they differ in different types of viruses. Thanks 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 of them even contain enzymes.
Begin the breeding process
Viruses are considered absolute parasites. They cannot live unless they cause harm. Their pathologic althe action is based on the fact that, by multiplying, they kill the cell in which they are located.
You can understand how this process occurs if you consider in detail how the microorganism enters the cell, and what happens in it after that. Virions can be thought of as a particle consisting of DNA (or RNA) enclosed in a protein sheath. Reproduction of viruses begins only after the microorganism is attached to the cell wall, to its plasma membrane. It must be understood that each virion can only attach to certain types of cells that have special receptors. One cell can accommodate hundreds of viral particles.
After that, the process of viropexis begins. The cell itself draws in the attached virions. Only after that begins the "undressing" of viruses. With the help of the complex of enzymes entering the cell, the protein shell of the virus dissolves and the nucleic acid is released. It is she who passes through the channels of the cell into its 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 integrated into 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 are connected to ribosomes, where the process of synthesis of new proteins takes place.virus.
As soon as enough virus components have 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 viruses reproduce.
In the composition of the newly formed virions, particles of the cells in which they were located can be detected. Often the process of their formation ends with the fact that they are enveloped in a cellular membrane layer.
Completion of reproduction
As soon as the composition process ends, the viruses leave their first host. The formed offspring leave and begin to infect new cells. Viruses reproduce directly in cells. But in the end they are completely destroyed or partially damaged.
Having infected new cells, viruses begin to multiply actively in them. The reproduction cycle is repeated. How the generated virions will exit depends on the group of viruses to which they belong. For example, enteroviruses are characterized in that they are rapidly released into the environment. But herpes agents, reoviruses, orthomyxoviruses come out as they mature. Before they die, they can go through several cycles of such reproduction. At the same time, cell resources are depleted.
Disease Diagnosis
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 crystal-like clusters. Experts call them bodiesinclusions.
For example, with influenza, smallpox or rabies, such accumulations are found in the cytoplasm of cells. In spring-summer encephalitis, they are found in the nucleus, while in other infections they can be both there and there. This sign is used to diagnose diseases. In this case, it is also important where exactly the process of virus reproduction takes place.
For example, when oval or round formations are found in epithelial cells, they speak of smallpox. Cytoplasmic accumulations in brain cells are indicative of rabies.
The way viruses reproduce is very specific. First, the virions enter the cells that suit them. After that, the process of releasing nucleic acids and creating "blanks" of parts for future pathogenic microorganisms begins. The reproduction process ends with the completion of new virions that are released into 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 produce defective offspring.
