Orthomyxovirus infections are a group of diseases with a fairly wide spectrum of action, from highly contagious to low-pathogenic. The causative agents of these infections are usually classified as RNA viruses with a diameter of 70 - 400 nm. At the same time, the size and arrangement of structural details of these viruses are sufficiently diverse for specialists working with them to understand that this is a group of pathogens of the same type.
The causative agents of orthomyxovirus infections usually multiply in cells of the early stages of development. Provocateurs of the first, rapidly developing acute form of the disease overcome cellular barriers and accumulate in the cytoplasm. The conditions for the transition from the initial stage of the disease are the introduction of the virus into enterocytes, epithelial cells of the respiratory tract, and hepatocytes. Viruses are able to multiply actively for some time, after which they penetrate into more distant areas of the organs, and the resulting disease progresses. Meanwhile, the infection can pass from one host to another. Since viruses contain antigens identical to human or mammalian proteins, they are quickly recognized and immune reactions are induced. After rapid onset of the disease, immune responses weaken as the viral concentration in the bloodstream decreases. Despite the partial apeptia of viral antigens due to a decrease in the immune response and the stability of interferons, complete ridding of the body from viral invasion is possible only when the recovery phase is reached. The end of the disease usually occurs against the background of activation of the immune system to complete the localized manifestations of the disease.