Synonyms
Influenza, real influenza, virus influenza influenza viruses are surrounded by a shell, a so-called lipid double membrane, on the surface of which various features are present that are visible as spikes under the electron microscope. The two most important of these surface features are haemagglutinin (antigen H) and neuraminidase (antigen N). On the basis of these two characteristics the influenza viruses of the type A can still be divided into different subgroups.
There are at least 15 different forms of haemagglutinin and 9 types of neuraminidase that are known to date for influenza type A. The so-called swine flu or Mexican flu, which spread worldwide in winter 2009/2010, is an influenza virus type A with the surface characteristics H1N1. The pandemic of 1918/1919, the so-called Spanish flu, was also an influenza virus type A with the characteristics of H1N1.
After contact with influenza viruses, they connect to the cells of the respiratory tract and mucous membranes via the haemagglutinins on their surface. The haemagglutinin also causes the envelopes of the virus and host cell to fuse, so that the influenza virus can begin to multiply inside the cell. Viruses, such as the influenza viruses, do not have their own metabolism and cannot multiply on their own without help.
They need other cells to do this for them. This distinguishes them mainly from bacteria, which have their own metabolism and can reproduce on their own. After the viruses have successfully reproduced, they cause the cell to expel them. In order to prevent the viruses from getting stuck to the same cell again with their contact mechanism haemagglutinin, the surface feature neuraminidase blocks this mechanism. The body cell dies when the viruses escape, which causes, among other things, the symptoms of disease, and the newly produced viruses swarm out and infect other cells.
Duration of symptoms
After infection with viruses, which are the cause of influenza, the typical symptoms do not appear immediately. First, the so-called incubation period follows, which usually lasts about 1-2 days. During this time, the viruses already spread in the body, but do not yet cause any symptoms.
The symptoms begin about two days after infection with the virus. Especially the sudden onset of fever is of particular importance here. How long the typical symptoms of influenza last varies greatly from individual to individual.
In most cases, the symptoms last about 5-7 days, although it can take several weeks until all symptoms have disappeared completely. This depends above all on the body’s own defenses, which fight the virus. If the immune system is strong, the defence against the virus is relatively successful. In people whose immune system is weak, such as the elderly or people with previous illnesses or who are taking certain medications, a complete recovery may take longer and may require drug therapy.