THE ROLE OF AMNIOTIC PASSAGE IN THE EGG-ADAPTATION OF HUMAN INFLUENZA-VIRUS IS REVEALED BY HEMAGGLUTININ SEQUENCE ANALYSES

Obtaining an isolate of a human influenza virus in the allantoic cavit y of the embryonated hen's egg is more efficient if the clinical sampl e is initially passaged in the amniotic cavity. To investigate the ext ent to which the variants present after allantoic propagation are also selected by amniotic passage, clinical virus passaged once in the amn ion has been subjected to extensive genetic and antigenic analyses. Th e data indicate that the natural virus can replicate unrestrictedly wi thin the amnion. However, exposure of amniotic virus to the allantois during the incubation period, which will occur through the hole betwee n the amniotic and allantoic cavities caused by the inoculating needle , allows for the possibility of an egg-adapted variant establishing re plication within the allantois and returning to the amnion. These obse rvations illustrate why prior passage in the amnion increases the prob ability of a variant successfully establishing itself during a subsequ ent allantoic passage.