Avian influenza can cause a wide range of symptoms, ranging from a mild form to a rapidly fatal and highly contagious disease that leads to severe outbreaks, particularly in poultry farms. The highly pathogenic H5N1 virus, which has been spreading in Asia since December 2003, causes a devastating disease in birds and an epidemic unprecedented in its severity and scope. Its initial consequences are economic, in countries where poultry farming forms the basis of subsistence agriculture. The impact on human health has so far been limited to several dozen deaths. However, given the significant potential for influenza viruses to mutate, the adaptation of H5N1 to humans is a real threat justifying the development of plans to combat the possible outbreak of a pandemic. (Introduction)