Unité de génétique moléculaire des virus respiratoires, URA 1966 CNRS,
Institut Pasteur, 25, rue du Dr-Roux, 75724 Paris Cedex 15
To encompass the wide spectrum of host species harbouring a multitude of various viruses, an ecological approach to the diversity of influenza viruses (IVs) is necessary. Aves are the corner stone of the world of IVs. Birds represent a zoonotic pool of viruses and their biology, e.g. migrations, exerts a direct impact on global viral circulation. In the case of IVs, interspecies barriers are relative and viral transmission from birds to mammals has been well documented. Even though such an event was observed with humans, pigs remain a contender for the role of mixing vessel and transmission link. The mechanisms leading to the emergence of a virus, prone to cross interspecies barriers and to establish itself into a new mammalian host, are not yet well understood. Once in a new mammalian host, IVs undergo rapid evolution, whereas in birds they remain in an evolutionary stasis, resulting probably from an ancestral equilibrium.