At the end of maturation,mature virions are released,either as a result of cell lysis or by budding or excretion,depending on the virus. The number of virions released,called the burst size,varies with the particular virus and the particular host cell,and can range from a few to a few thousand. The duration of the virus replication cycle varies from 20-60 min (in many bacterial viruses) to 8-40 h (in most animal viruses). Because the release of virions is more or less simultaneous,virus replication is typically characterized by a noe-step growth curve (figure 9.9). In the next two sections we consider a few key steps of the virus replication cycle in more detail.