Viruses are elementary units, consisting of an independent parasite particle. They infect whatever living organism (including fungi and bacteria), profiting from them as vehicle to rapidly spread under suitable conditions. Structures and ambiences with a high concentration of people and transits are the ideal virus proliferation and spreading backgrounds. Some of the main virus strains present in the environment once on any surface are vital maximum for 35 days. As a consequence a correct sterilisation procedure and use of suitable products are required to prevent and hinder epidemics.

The immune system, if correctly supported, initially can fight any viral attack, but for immune-deficient people common viruses such as Adenovirus, Enterovirus and Norwalk virus can be extremely dangerous. Virus which are not highly dangerous such as Paramyxovirus (provoking measles), Rotavirus and Rubella virus if attacking immune-deficient people can lead to severe consequences. What is more at present virus contagions are reported for diseases which used to be controlled in the Westerns countries such as B and C hepatitis, Poliovirus. The most probable infection source is the mouvement of people and goods which are not controlled from countries where such viruses are still present. Among others, the HIV and SARS viruses are lethal in 15% of the cases as well as the avian or bird flu, which consistently spread in the last few years all over the world.