Infectious bovine rhinotracheitis virus in bovine kidney cells: II. Virus development and ultrastructural alterations in cultured cells

The sequence of events in the development of infectious bovine rhinotracheitis (IBR) virus and the attendant ultrastructural alterations in permissive bovine kidney cell (BKC) cultures were studied by determining a single-step growth cycle of the virus and by electron microscopical examination of monolayer cell cultures. During the latent phase of the growth cycle, alterations in the infected cells suggested that there was an active synthesis of proteins. In the second or logarithmic growth phase, the infected cells revealed viral particles in various stages of assembly. The first discernible viral form in the genesis of an IBR virus particle appeared to be a partially or a fully assembled viral capsid. Viral forms found subsequently in the course of virion development were, in turn, the capsids with light cores, and then capsids with dense nucleoids and finally enveloped virus particles. In addition, unique ultrastructural alterations of the infected cells involved nearly all of the cellular organelles. For example, the endoplasmic reticulum of these cells appeared to be modified into channels for the release of virus particles. In the final phase of infection that was characterized by a decline in virus yield, the cells progressively degenerated.