Flu (INFLUENZA, GRIPPUS) is an acute respiratory disease of viral etiology, proceeding with the symptoms of intoxication and defeat of the respiratory tract. It is an airborne anthroponosis and very dangerous for its complications.
This disease falls under the group of acute respiratory disease (ARD) or acute respiratory viral infection (ARVI).

The acute respiratory viral infections (ARVI) belong to the ubiquitous widespread diseases, which for a long time have been occurring more than any other infectious diseases together. According to WHO, one in every three inhabitants of the world gets sick with ARD each year. In Russia about 30 million cases of ARV are registered every year. Such frequent diseases of the respiratory tract are explained by wide variety of etiologic factors (there are more than 300 pathogens of respiratory infections) and by the fast and easy way the pathogens spread. Also there are highly contagious and changeable.

Researches in the sphere of immunopathogenesis of flu and other acute respiratory viral infections have shown that flu, like many other viral diseases, rudely disrupts a balanced system of cytokines. At the same time, it affects a helper-suppressor link cell-mediated immunity. Due to flu the decrease in immunological resistance and deep suppression of functional activity of various parts of the immune system lead, to an exacerbation of many chronic diseases, as well as the appearance of secondary bacterial complications. This makes it possible to regard ARVI as a factor that greatly increases the case rate in general and it gives special significance and urgency to the problem of treatment and prevention of these diseases.