The "in vivo" production of "new" influenza A viruses. I. Genetic recombination between avian and mammalian influenza viruses.

Abstract “New” influenza viruses were isolated from turkeys and pigs after mixed infection with influenza viruses under conditions where either both viruses replicated or where only one virus multiplied and replication by the other was not detectable. Stable antigenic hybrids containing fowl plague virus (FPV) hemagglutinin, and swine influenza virus neuraminidase and also the reciprocal recombinant viruses were isolated from pigs inoculated with swine influenza virus and FPV. (FPV does not multiply in pigs.) Antigenic hybrids containing FPV hemagglutinin and turkey influenza virus neuraminidase, and reciprocal hybrids containing turkey influenza virus hemagglutinin and FPV neuraminidase were isolated from turkeys mixedly infected with FPV and turkey influenza virus. The frequency of isolation of antigenic hybrid viruses from turkey lungs was high; one out of four plaques isolated contained a “new” virus. The “new” viruses were virulent for host animals causing either a severe, fatal disease or a mild respiratory infection. These studies provide formal evidence for genetic interaction between mammalian and avian viruses in vivo and provide some evidence for the possible origin of human pandemic influenza viruses.