[Could influenza virus produce the first pandemic of the XXI century?].

Since the last decade of the XX century has been increasing the frequency of outbreaks with highly pathogenic avian influenza viruses among poultry and direct transmission of these viruses to humans. These events have ignited great concern about the pandemic potential of these viruses, for that reason the study and characterization of the previously influenza viruses involved in pandemics or outbreaks has been considered of great importance. This review presents and compares the different influenza viruses involved in the XX century pandemics and outbreaks, with emphasis in the cellular receptors used by avian and human influenza viruses. And the recently finding that human respiratory tract contains both type of receptors, and finally which factors could allow a successful direct human infection with avian viruses, and how theses viruses could be transmitted among the human population.