Viral diseases There are many viral diseases. Let's talk about the most common ones. Let's start with the flu virus. There are many laboratories around the world who regularly completion of stockpile vaccines and drugs to treat it. The influenza virus is most studied infectious agents. It should be noted that the epidemic virus Grip occur every year, and every few decades the epidemic of influenza is becoming a pandemic. The influenza virus has the ability to quickly change their structure. These changes affect the surface proteins - antigens, which recognizes the human immune system. Immunity of a man who developed a in contact with a variety of virus is not able to recognize the other, and when she begins her infection recognize only after full development of the disease. Antigenic variation is the ability of the virus to change its structure. It is because of her flu occur regularly. This regularity is alien to other infections, and only because of it being infected with influenza most people. Antigenic variation is of two kinds. First - antigenic drift, the second - antigenic shift. Antigenic drift - it mutations affecting two major viral proteins - hemagglutinin (H), which provides introduction of the pathogen in human cells, and neuraminidase (N), which is responsible for the output of mutated viruses from the cell. The emergence of antigenic drift is due to the fact that the enzyme, which doubles the viral RNA in the process of creating new viruses, no function of protection against errors that occur during the synthesis. These errors and lead to a mutation of the pathogen. The very same process of antigenic drift leads to a gradual change in the structure of the influenza virus, which causes it to partial or complete neuznavaniyu human immune system. It is for this reason there is a need systematically change the antigens included in the flu vaccine. Antigenic shifts - are the most significant changes in the antigenic composition of the virus. Promotes emergence antegennyh shifts that influenza can affect not only human cells, but also of animals: pigs, horses, birds, etc. In cases where the body there is more than one species of the virus, is the exchange of entire genes between viruses, thereby producing new strains of influenza, which in most cases are more aggressive than the original ones. This process and called antigenic shift. Now a wide range of antiviral drugs that you can to *buy* in our *online pharmacy <http://superpills.blogspot.com/>*. The best effect of these drugs is achieved in situations where they are beginning to use when detecting the first symptoms of influenza infection, but they are also able to facilitate the course of the disease at any stage.