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Today, influenza is one of the most common diseases affecting all age groups. The disease is able, in addition to general discomfort, to cause some complications, sometimes - dangerous to health. Therefore, let's consider what is the flu, how this viral disease occurs, how the flu appears (symptoms of influenza a, b, etc.), as well as other questions about this disease.

Characteristics of the disease

Infectious diseases caused by RNA viruses of the Orthomyxoviridae family also include influenza. The size of this virus, on average, is 80 nm. It spreads rapidly around the world during seasonal epidemics, placing a significant economic burden on health care costs and productivity losses. The main genetic changes in the virus occurred in the 20 th century, when there were 3 epidemics or even pandemics that swept the whole world and affected millions of people.


There are 3 main types of viruses:

The most influenza is epidemics and pandemics. This is because these viruses can undergo significant antigenic variations and, therefore, find a new immune target in susceptible people or by their changes completely depreciate immunization with previous infections. The population is generally more resistant to viruses B and C, because these types do not have the ability to mutate and recombine, and any antigenic drift is usually negligible. It also leads to the fact that a person with a non-compromised immune system, as a rule, can get infected with B or C viruses only once in a lifetime. Symptoms of influenza A are similar to those of other types of viruses, their intensity depends on the individual's susceptibility.

Influenza A viruses can be further classified according to viral envelope glycoproteins - hemagglutinin (abbreviation HA or H) and neuraminidase (abbreviation NA or N) - which are necessary for the life cycle of the virus. In influenza A, 16 subtypes of H and 9 subtypes of N were identified, while 1 subtype H and 1 subtype N were identified for type B influenza virus. Currently, the most common antigen variants of influenza A virus are variations of H1N1 and H3N2 .

There are other variants of the virus, and therefore its specific stem sections were identified by a standard nomenclature indicating the type of virus, the geographical location of the first occurrence, the year of isolation, the serial number of isolation and the subtype HA and NA.

How does the flu occur?

Influenza viruses, like many infectious diseases, spread from person to person by a drip. The disease is caused by microscopic infectious particles of mucus and saliva containing a large number of viral particles. With active disease, viruses are present in large amounts in the secretions of the respiratory tract. The formation and release of drops occurs during coughing, sneezing, and also with normal speech. Droplets along with the surrounding air get inhaled into the respiratory tract of other people. Common ways of transmitting influenza viruses include kissing or even using common objects (cutlery, handkerchiefs).

The viruses are attacking!

The only purpose and mission of viruses is to multiply. Since they lack their own mechanisms that facilitate the replication of genetic information, they must use other cells for this purpose. In order to start copying, the virus must first "connect" to the cell. Binding of viruses to respiratory tract cells is mediated by the binding of viral hemagglutinin to their receptors on the surface.

To penetrate the virus into the cell, the ability of cells to "swallow" particles on its surface (so-called endocytosis). This is an action in which the cell wraps the virus on its own surfaces with cellular membranes. In this shell, she then swallows the virus inside. Here it comes to dissolving the protective envelope of the virus, so that it releases its genetic material (RNA). RNA moves to the nucleus of the cell where the copying takes place. Together with the copying of genetic information, the shells of future viruses are beginning to form. New RNA and other newly formed components migrate to the cell surface, where they form new viruses and leave the cell.

Under the surface

The entry of the virus into the cell is one of the main obstacles in its life cycle. Propagation of the virus blocks the mechanisms that the cell needs to create its own structures. Their production is significantly reduced or completely stopped. The cell gradually dies. In addition, the simple binding of the virus to the cell membrane changes its characteristics and functions. Viral proteins are included in the cell surface. The immune system considers mutating cells as foreign. By its defense mechanisms, it attacks and destroys them.

The course and symptoms of influenza are caused, both by local damage of cells in the airways, and by the general reaction of the immune system. Reproduction of viruses can be manifested by swelling and damage to the mucous membrane of the respiratory tract. Time after exposure to the virus at the onset of symptoms (incubation period) is short. It ranges from 18 to 24 hours.


In view of the short incubation period (18-24 hours), the disease can manifest itself very suddenly and without warning, practically, with complete health. Despite the fact that the virus penetrates the body through the mucous membranes of the respiratory system, the first symptoms of the flu are, surprisingly, neither rhinitis nor cough.

Fever and pain

The disease usually begins with a high temperature (38-40°C). The rise in temperature is usually accompanied by chills. To these signs is added a strong headache. Flu is an ailment, also manifested by photophobia and rigidity of the occipital muscles. The course of the disease is also often accompanied by pain in the joints, muscles, eyes, back and legs. All these signs are accompanied by considerable fatigue. Another possible symptom is nausea, sometimes vomiting, diarrhea, constipation, or loss of appetite.

Within the next one or two days, the course of the disease acquires the classic features represented by the symptoms of respiratory system disorders. It's about the common cold, pain and burning in the throat, dry cough. Cough changes over time into a productive cough.

Fever, fatigue, headache and muscle pain, usually disappear within three or four days. Runny nose and cough last from a week to ten days. Increased fatigue and weakness can, to varying degrees, continue for a month after the disappearance of the main symptoms.

The course of the disease depends on several factors. With respect to what signs and to what extent will manifest, the most important point is the age of the patient, his general stability and the presence of other co-morbidities.

The usual course of influenza

The course of the disease, as already mentioned above, depends on the person's age, the general resistance of the body and the presence of any other concomitant disease.

Onset of the disease, day 1

Next 1-2 days

At this time, there are classic symptoms of respiratory disease:

Further progress of the disease


The flu usually occurs in large outbreaks in the spring and autumn. Remember some simple tips on how to avoid the disease. The only 100 percent recipe does not exist. Nevertheless, there are ways how to significantly reduce the risk of influenza, or at least mitigate the course of the disease.

Limit contact with the virus!

This is the first option. In the period of increased "binge" of influenza, avoid the presence of a large number of people in society. Do not visit cinemas and theaters. Minimize and movement on public transport.

Support the immune system!

Increase the intake of vitamins and fluids. In case you can not provide vitamins with food intake, you can purchase multivitamin preparations at the pharmacy. In addition to vitamin C, the diet should also contain zinc and selenium. Heat dress well.


The main prerequisite for effective prevention is a healthy and enduring organism. In this case, a person has a much greater chance of resisting an infection than with a weakened organism. Strengthen the body can help the following steps: