The health check established for avian influenza by the competent units is not only linked to the economic impact deriving from animal deaths, but also raises particular concerns for public health . What most worries experts is that new viral subtypes become able to cause disease in humans and, above all, to be transmitted from person to person. Influenza viruses belonging to type A, in fact, undergo phenomena of genetic reassortment with high frequency; this allows remarkable capacity of adaptation to new guests and determines the continuous appearance of new viral strains . These mutations can occur, for example, when a human virus and an avian virus "exchange" their genetic heritage or when the virus passes from one animal species to another (the passage from birds to pig is particularly dangerous). There is, therefore, the possibility that from an animal tank may originate a new virus for which man is susceptible (as happened in the last century, for example, with the Spanish from virus A-H1N1 of 1919 or the Asian from A-H2N2 of 1957).
The eventual inter-human transmission would allow the disease to spread globally, thus causing an avian influenza pandemic . Currently, the viruses with the highest pandemic potential remain H5N1 and H7N9 as they continue to circulate among chickens and can cause severe disease in people. Other virus subtypes could trigger a pandemic, but the risk is considered lower.
