HSV illustrates an interesting property of certain viruses - it can take both active and latent forms. During the active phase, the virus interferes with the cell's normal metabolism, causing the symptoms associated with the disease - including painful genital blisters. During the latent phase, it's as if the virus has gone to sleep. Although the host cells remain infected, the host is a symptom-free carrier of the disease. We now know the difference between the active and latent manifestations of viral infection is a result of a switch in viral replication patterns.
Some viruses can only replicate by what is called the lytic pathway.
They enter and inject a host cell with DNA, forcing it to make new viruses. At some point bursting at the seams with the viruses, the host breaks open, releasing new pathogens into the environment. This latter pathway is called the temperate or lysogenic pathway. At that time, it was known that some bacterial cultures that grew normally and otherwise seemed perfectly healthy were actually infected by phage. Although the phage didn't seem to interfere with the host bacteria, such cultures had the ability to cause the lysis or rupture of other bacteria.