Almost every year, especially in the autumn-winter period, doctors warn of a high incidence of influenza. How do new influenza viruses appear?
What are the flu viruses?
At the moment, specialists have discovered 4 types of influenza viruses, which are indicated by the letters A, B, C and D. Each type has unique features, on the basis of which it was assigned a separate category.
Influenza A virus
Virus A - the most common and most often causes outbreaks, epidemics, pandemics. It is characterized by high variability and, accordingly, rapid spread. Waterbirds are considered the source of influenza A, from which the disease can be transmitted to humans through the chain. It is divided into many serotypes (subtypes). Among them, the most famous are H1N1 (Spanish, swine flu), H5N1 (bird flu).
Influenza B, C, and D viruses
The influenza B virus is also variable, but not so intense. Epidemics occur less frequently - approximately every 4-6 years. The virus is very similar to A, so sometimes they are difficult to distinguish. Often these viruses are activated simultaneously. C and D are considered non-hazardous to humans. Influenza C virus is more stable than the previous ones and can only cause mild infections. D does not cause disease in humans at all.
All four types of influenza virus are united by the fact that they belong to the same family - orthomyxoviruses. These are viruses that contain RNA - ribonucleic acid.She is responsible for genes, their coding, reading, regulation and expression.
Interesting fact: the first flu virus was discovered in 1901 in chickens (Italy). However, then they still did not know about the existence of such a disease as the flu, so it was attributed to the bird plague. Scientists were able to correctly assess the influenza virus only after 50 years.
How do new influenza viruses appear?
The annual appearance of new types of influenza virus is due to their high variability. To understand the origin of this property, you need to have an idea about the structure of the virus and its effect. The infectious part is a spherical virion. Inside it contains special proteins called neuraminidase and hemagglutinin.
These proteins are the main cause of the variability of the virus, as well as its rapid spread. When a virus enters the body, it begins to attack its cells. In this case, he first attaches to the cell, and then penetrates inside. Hemagglutinin is necessary for penetration into the cell, and neuraminidase allows the virus to leave the infected cell.
Also inside the virion is the virus genome, which contains its genetic information in the form of RNA. Often, infection with one virus may be accompanied by the emergence of another. For example, A and B often attack the body at the same time. Moreover, if two similar viruses are contained in the cell of the body together, they are able to exchange genetic information with each other. Thus, new subtypes of influenza viruses are formed. And this process is called antigenic shift or shift.The new virus subtype will have properties common to the two source viruses.
Interesting fact: experts share two phenomena - antigenic variability and antigen drift. If in the first case the formation of a new virus occurs very quickly, then the second option implies a slow and gradual mutation. It inevitably occurs with all influenza viruses, so it is impossible to invent an effective vaccine or develop immunity.
Specialists in the field of medicine are trying to foresee the occurrence of influenza epidemics in advance. To do this, they carefully study all cases of infection with any influenza virus, analyze the collected materials and work on creating effective vaccines. If you feel the first signs of the disease, it is important not to self-medicate, but to seek help from a qualified doctor.
The regular appearance of new influenza viruses is due to their structure and properties. The infectious part of the virus is the virion. Inside it contains the RNA genome with genetic information and proteins - hemagglutinin and neuraminidase. With their help, the virus penetrates into the cells of the body, and also leaves them. Thanks to this, the influenza virus spreads very quickly, and is also variable. When two similar viruses, for example, A and B, appear in the cell, they acquire the ability to exchange genes. So new viruses are formed, and their diversity is practically unlimited. Therefore, the body cannot develop a stable immunity.
