Investigation of biological properties and genome structure of recombinant influenza A virus strains differing by degrees of virulence for humans.

: The genome structure and some biological properties of parental and recombinant strains of influenza viruses differing by degrees of virulence for man were studied. The vaccine A/Leningrad/9/46 (H0N1) strain was shown to be markedly toxic and pathogenic for mice in contrast to influenza A/Brazil/11/78 and A/Victoria/35/72/50 viruses completely devoid of these properties. The recombinants deriving all 6 genes of the inner proteins of influenza A/Leningrad/9/46 strains and hemagglutinin and neuraminidase of the epidemic A/Brazil/11/78 strain have completely lost their pathogenicity for mice but acquired marked virulence for man. No such effect was observed in recombination of A/Brazil/11/78 with another vaccine strain, A/Victoria/35/72/50. It is suggested that the toxic properties of influenza virus are coded for in genes of internal proteins whereas their manifestation in one or another host species depends on the function of surface polypeptides.