First identified in Italy over a century ago, avian influenza is a disease of birds caused by a type A influenza virus, which can be classified as either highly pathogenic or low pathogenic. Avian influenza is common throughout the world and affect almost all species of birds. Hosts can be infected with either a mild form of the disease or the highly-pathogenic and more contagious forms, which are responsible for acute outbreaks. If caused by a highly-pathogenic virus, the disease has a sudden onset and, in almost 100% of cases, a rapid fatal course. Reports of birds-to-human transmission of the avian influenza virus have sparked fear of a new pandemic and led to the implementation of extraordinary preventive measures across the world.