Studies on the origin of pandemic influenza: IV. Selection and transmission of “new” influenza viruses in vivo

Abstract

The emergence of recombinant influenza viruses as dominant strains after recombinant in vivo was studied in an avian system. Turkeys possessing low levels of antibodies to the hemagglutinin of turkey influenza virus and to the neuraminidase of fowl-plague virus were mixedly infected with fowl-plague virus and turkey influenza viruses. Recombinant influenza viruses possessing the hemagglutinin of FPV and the neuraminidase antigen of turkey influenza virus became the dominant viruses present and killed the turkeys. These recombinant influenza viruses spread under natural conditions of transmission to contact turkeys and caused a miniepidemic of disease. The recombinant viruses were genetically stable but differed in transmissibility. Some failed to transmit to contact birds while others were highly transmissible and highly virulent. These studies suggest a mechanism of recombination, selection, and transmission consistent with the emergence of new pandemic strains of influenza viruses.