[Mechanism of the emergence of pandemic influenza virus strains and their control measures].

The 1957 Asian H2N2 and 1968 Hong Kong H3N2 pandemic strains of influenza are genetic reassortants between avian viruses and human strains. Since avian viruses of any subtype can contribute genes in the generation of reassortants in pigs, none of the 15 HA and 9 NA subtypes can be ruled out as potential candidates for future pandemics. The H5N1 influenza virus transmission from domestic poultry to humans in Hong Kong in 1997 further emphasized the need to have information on influenza viruses in avian species. For the prediction and control of future pandemics, the program of global surveillance of animal influenza has been started. Influenza virus isolates from animal species should be thoroughly characterized and be provided for the use of diagnosis and vaccine preparation.