Initially inapparent (covert) viral infections in which an equilibrium between the virus and the host has been established. Pathology may occur periodically, or chronically at a low level. If manifested in degenerative diseases of the central nervous system, these infections may result in death. The basis of these infections is an uncharacteristically low level of viral replication which may persist throughout the normal lifetime of the host, and which may follow the recovery from a more severe bout with the virus. The acute illness may have elicited production of antibodies, and an equilibrium between virus neutralization and antibody generation is established which may produce life-long immunity.