Causative agent of influenza

The causative agent of influenza is a microorganism that, when released into a living organism, is capable of causing the reproduction of its own cells in the tissues of the epithelial lining of the upper respiratory tract, causing a violation of the integrity of the cells and their death. Through damaged epithelial barriers, the virus enters the bloodstream and spreads throughout the body. Influenza is a particularly dangerous infectious disease that causes epidemics among the population almost every year. Almost every flu epidemic takes on the character of a natural disaster, causing great damage to public health. The disease affects all groups of the population, but pregnant women, children aged 6-9 months, the elderly and people with chronic diseases are at greatest risk of developing complications.

The causative agent of influenza is a virus that is able to very often change its antigenic structure, which leads to the fact that the human immunity formed after one disease does not protect against repeated illness of influenza of another antigenic structure (other strain). Bacteria are not the causative agents of influenza infection, they can accumulate on a weakened body, causing numerous and serious bacterial complications.

Types of infection

Influenza virus belongs to the genus Influenzavirus, belongs to the family of RNA-containing orthomyxovirus Orthomyxoviridae. By the difference in their own antigens, influenza viruses are divided into types A, B and C.

The most dangerous in the virus of this type is its tendency to antigenic variability, which leads to the failure of the developed immunity in the first case of infection. In other words, if a person has been ill with the flu, he has developed immunity to this type (strain) of the virus, however, in a short period of time the virus has slightly changed and for the body it already becomes a new disease that will be transferred as hard as the previous one.

Viruses spread among people through the airborne droplets - the fastest and most contact way, leading to rapid epidemic situations. Excretion occurs with saliva and phlegm when coughing, sneezing, talking, which in the form of a fine aerosol is distributed in the air and inhaled by other people. In some cases, it is possible to implement a contact everyday transmission path, and through the dishes, toys. The ability to mutate and the high contagiousness of influenza forces scientists to constantly work on new, more effective vaccines against the disease in order to prevent an outbreak of new epidemics.

The most dangerous viruses are influenza A-type. They are able to affect not only people, but also birds and animals. A viruses have high pandemic properties due to the fact that 2 antigens in their composition can constantly mutate. The formula of the influenza virus is composed of two subtypes of surface antigens - hemagglutinin, which ensures the entry and fixing of infection in the cells of the human body, and neuraminidase, which provides the processes of virus propagation in the cell and its subsequent migration to other human cells. Thus, in the H1N1 swine flu formula, the letter H stands for hemagglutinin antigen, and the letter N stands for neuraminidase.

These antigens easily and quickly change, leading to the constant emergence of the latest strains of influenza. In the modern world, there are about 2 thousand strains of this virus. This explains the annual outbreaks of the epidemics of this infection in all parts of the world. Scientists have not yet found out the reasons for this ability to modify the virus, so it is currently impossible to stop this process. At the same time, A-type viruses provoke an epidemic situation with regularity once every 2-3 years, B-types do it less often - once every 4-6 years, and C-type viruses are not epidemiologically dangerous.

Thus, influenza A is considered the most dangerous and capable of variability. It is the influenza A viruses that are responsible for the emergence of pandemics and severe epidemics. It is very stable, it can be stored at a temperature of 40 degrees for 2-3 weeks, which makes it dangerous to human health. For comparison, other influenza serotypes cannot withstand temperatures already at 37-37.5 degrees and die.

Variability of the A virus occurs when the hemagglutinin and neuraminidase indicators change. So, the variability of hemagglutinin by point mutations in a gene is called antigenic drift. If a complete gene replacement occurs, antigenic shift occurs. This causes not just a high incidence of disease, but real pandemics, similar to the one that happened in the world at the beginning of the 20th century and is known as the Spanish flu.

Less dangerous for humans, but no less significant in nature, influenza viruses of types B and C. Only the B-type virus is able to mutate with the drift type, the C-type virus remains unchanged. This indicates that only viruses of A and B types can participate in epidemic situations.

Any influenza virus must have its own territory for survival. For all of them, they are living organisms. A-type flu can survive in human and animal organisms, and influenza types B and C can live exclusively in humans. At the same time in the external environment, many such viruses are able to exist up to 4 hours. A-type influenza is most resistant to survival, sometimes it can survive in a dried drop on bedding for 10-11 days. House dust can keep A-type flu for up to 5 weeks at certain temperatures. Influenza viruses die when wet cleaning with the use of any antiseptic. In order to kill all the remains of the virus in the room where the patient with the flu was, it is enough to simply ventilate it.

New viruses

Among the newest strains of influenza in 2017–2018, the flu virus called Michigan, which is a subtype of the swine flu virus (A / Michigan / 45/2015 (N1H1)), is most prominent. Such a name code helps scientists to easily understand the year in which the strain was first discovered, and which antigenic structure it has to deal with. All this facilitates diagnostic measures in patients and the appointment of effective therapy.

It is already known that the Michigan virus is highly likely to cause all kinds of serious complications. Also, this strain is very contagious, which can lead to numerous epidemics. Mutations of this strain are explained by the fact that it is able to extract new genes from animal organisms into which it falls, surviving in them, but not causing infection.

The virus of Michigan, penetrating into a human cell, will rearrange its DNA code, using life-supporting properties for its own replication. At the same time, the genes of the virus enhance human proteins, which, as a result, increase the aggressiveness of influenza on the human body and prevent its disintegration.

A critical role in the recovery of a Michigan flu patient is played by how quickly he went to the doctor at the initial stage of the illness.

The main manifestations of this strain of the disease include:

  • the incubation period from 2 hours to a week, most often it lasts up to 72 hours;
  • a sharp onset of the disease, which will be the more intense, the higher the concentration of the virus that simultaneously enters the human body;
  • extremely high body temperature from the very beginning of the disease, reaching 39-41 degrees;
  • pronounced signs of intoxication - weakness, drowsiness, weakness, aching, headaches;
  • in severe cases, signs of encephalopathy with convulsive seizures, hallucinations, vomiting, as well as vascular disorders, manifested by nosebleeds, punctate hemorrhages in the soft palate.
  • the presence of hyperemia of the mucous membranes of the eyes and puffiness of the face;
  • the presence of burning pain in the sternum;
  • the occurrence of nasal congestion, nasal congestion without the typical manifestations of rhinitis.

Symptoms of Michigan flu will be expressed as much as the patient’s immune system feels at the time of the infection. If a person has chronic illnesses, he will most likely endure the flu of Michigan Michigan, quite likely.

To protect against this strain of influenza, a new highly effective vaccine has already been developed, the vaccine of which will help not to get the infection and protect itself from the many serious complications that it leads to.

Ways of infection

Influenza is an easily transmitted disease spreading in air masses from person to person. The most dangerous for others are those who are already infected with the virus, even in the case when the incubation period has not expired and the person himself does not feel sick. After the manifestation of the symptoms of the disease, the infectivity remains at a high level for up to 7 days, and then decreases several times, however, a completely ill patient becomes epidemiologically safe only after 10-14 days from the onset of symptoms.

The airborne droplet spread of the flu leads to the fact that the disease forms epidemics, to which young children, pregnant women, the elderly, people suffering from chronic diseases are especially sensitive. These categories of people can become infected even when they come in contact with a small amount of the virus.

Also, the flu is transmitted from person to person and through the contact-household way, through household items, dishes, and hygiene products. In order to ensure that those who live and are always close to him are not injured in identifying one sick person, doctors advise isolating the patient, giving him separate household items, dishes and towels.

In air, influenza can survive without a human body from 2 to 9 hours, on paper - from 8 to 12, and on metal - 24-28 hours. After entering the human body on the mucous membrane of the respiratory tract, viruses attach to the cell with hemagglutinin. The enzyme neuraminidase destroys the cell membrane of the mucosa, and the virus penetrates the cell, destroying it. Viral RNA is replicated and viral particles are assembled. New viruses are released and infect other cells. Some of the virus that has entered the body remains in place, going outside when talking, coughing, sneezing, and infecting others in this way.

Seasonality of the flu virus

Influenza infection has a seasonal spread among people, because the survival of its particles directly depends on air temperature and humidity. The risk of epidemics is highest at temperatures from +5 to −5, when a decrease in air humidity creates favorable conditions for viruses to enter the human body, due to cooling and dry airways.

Low solar activity and the lack of vitamin D in the surrounding area also contribute to the "prosperity" of the infection.

From autumn to spring, the virus spreads easily in the environment, gradually striking entire groups of people. Schoolchildren and students in secondary specialized educational institutions, medical personnel of medical institutions, transport and service workers also belong to groups of high risk of infection. This should also include military units, barracks, where optimal conditions are created for the transmission of the pathogen. Flu spreads when sneezing or coughing at a distance of about 3.5 meters.

Already infected people (virus carriers) act as a source of infection. If, at a specific time period, a new or mutated strain of influenza arrives in the region, then its accelerated spread with the formation of epidemics is possible. Flu epidemics caused by serotype A occur approximately every 2-3 years, and caused by serotype B every 4-6 years.

The author of the article:
Medvedeva Larisa Anatolevna

Specialty: therapist, nephrologist.

Total experience: 18 years.

Place of work: Novorossiysk, medical center "Nefros".

Education: 1994-2000 Stavropol State Medical Academy.


  1. 2014 - "Therapy" full-time advanced training courses on the basis of the State Budgetary Medical Educational Institution of Higher Professional Training "Kuban State Medical University".
  2. 2014 - "Nephrology" full-time refresher courses on the basis of the Stavropol State Medical University.
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